deps: update V8 to 6.6.346.23

PR-URL: https://github.com/nodejs/node/pull/19201
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

34 files changed, 1526 insertions, 931 deletions

diff --git a/deps/v8/src/heap/concurrent-marking.cc b/deps/v8/src/heap/concurrent-marking.cc
index 44ab099ba8..3aafd191cc 100644
--- a/deps/v8/src/heap/concurrent-marking.cc
+++ b/deps/v8/src/heap/concurrent-marking.cc
@@ -424,18 +424,11 @@ ConcurrentMarking::ConcurrentMarking(Heap* heap, MarkingWorklist* shared,
       shared_(shared),
       bailout_(bailout),
       on_hold_(on_hold),
-      weak_objects_(weak_objects),
-      total_marked_bytes_(0),
-      pending_task_count_(0),
-      task_count_(0) {
+      weak_objects_(weak_objects) {
 // The runtime flag should be set only if the compile time flag was set.
 #ifndef V8_CONCURRENT_MARKING
   CHECK(!FLAG_concurrent_marking);
 #endif
-  for (int i = 0; i <= kMaxTasks; i++) {
-    is_pending_[i] = false;
-    task_state_[i].marked_bytes = 0;
-  }
 }
 
 void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
@@ -443,13 +436,8 @@ void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
                       GCTracer::BackgroundScope::MC_BACKGROUND_MARKING);
   size_t kBytesUntilInterruptCheck = 64 * KB;
   int kObjectsUntilInterrupCheck = 1000;
-  LiveBytesMap* live_bytes = nullptr;
-  {
-    base::LockGuard<base::Mutex> guard(&task_state->lock);
-    live_bytes = &task_state->live_bytes;
-  }
-  ConcurrentMarkingVisitor visitor(shared_, bailout_, live_bytes, weak_objects_,
-                                   task_id);
+  ConcurrentMarkingVisitor visitor(shared_, bailout_, &task_state->live_bytes,
+                                   weak_objects_, task_id);
   double time_ms;
   size_t marked_bytes = 0;
   if (FLAG_trace_concurrent_marking) {
@@ -458,9 +446,9 @@ void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
   }
   {
     TimedScope scope(&time_ms);
+
     bool done = false;
     while (!done) {
-      base::LockGuard<base::Mutex> guard(&task_state->lock);
       size_t current_marked_bytes = 0;
       int objects_processed = 0;
       while (current_marked_bytes < kBytesUntilInterruptCheck &&
@@ -484,17 +472,16 @@ void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
       marked_bytes += current_marked_bytes;
       base::AsAtomicWord::Relaxed_Store<size_t>(&task_state->marked_bytes,
                                                 marked_bytes);
-      if (task_state->interrupt_request.Value()) {
-        task_state->interrupt_condition.Wait(&task_state->lock);
+      if (task_state->preemption_request.Value()) {
+        TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                     "ConcurrentMarking::Run Preempted");
+        break;
       }
     }
-    {
-      // Take the lock to synchronize with worklist update after
-      // young generation GC.
-      base::LockGuard<base::Mutex> guard(&task_state->lock);
-      bailout_->FlushToGlobal(task_id);
-      on_hold_->FlushToGlobal(task_id);
-    }
+    shared_->FlushToGlobal(task_id);
+    bailout_->FlushToGlobal(task_id);
+    on_hold_->FlushToGlobal(task_id);
+
     weak_objects_->weak_cells.FlushToGlobal(task_id);
     weak_objects_->transition_arrays.FlushToGlobal(task_id);
     base::AsAtomicWord::Relaxed_Store<size_t>(&task_state->marked_bytes, 0);
@@ -517,21 +504,21 @@ void ConcurrentMarking::ScheduleTasks() {
   DCHECK(heap_->use_tasks());
   if (!FLAG_concurrent_marking) return;
   base::LockGuard<base::Mutex> guard(&pending_lock_);
+  DCHECK_EQ(0, pending_task_count_);
   if (task_count_ == 0) {
-    // TODO(ulan): Increase the number of tasks for platforms that benefit
-    // from it.
-    task_count_ = static_cast<int>(
-        V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads() / 2);
-    task_count_ = Max(Min(task_count_, kMaxTasks), 1);
+    task_count_ = Max(
+        1, Min(kMaxTasks,
+               static_cast<int>(V8::GetCurrentPlatform()
+                                    ->NumberOfAvailableBackgroundThreads())));
   }
   // Task id 0 is for the main thread.
-  for (int i = 1; i <= task_count_ && pending_task_count_ < task_count_; i++) {
+  for (int i = 1; i <= task_count_; i++) {
     if (!is_pending_[i]) {
       if (FLAG_trace_concurrent_marking) {
         heap_->isolate()->PrintWithTimestamp(
             "Scheduling concurrent marking task %d\n", i);
       }
-      task_state_[i].interrupt_request.SetValue(false);
+      task_state_[i].preemption_request.SetValue(false);
       is_pending_[i] = true;
       ++pending_task_count_;
       Task* task = new Task(heap_->isolate(), this, &task_state_[i], i);
@@ -540,6 +527,7 @@ void ConcurrentMarking::ScheduleTasks() {
           task, v8::Platform::kShortRunningTask);
     }
   }
+  DCHECK_EQ(task_count_, pending_task_count_);
 }
 
 void ConcurrentMarking::RescheduleTasksIfNeeded() {
@@ -553,25 +541,24 @@ void ConcurrentMarking::RescheduleTasksIfNeeded() {
   }
 }
 
-void ConcurrentMarking::WaitForTasks() {
-  if (!FLAG_concurrent_marking) return;
+bool ConcurrentMarking::Stop(StopRequest stop_request) {
+  if (!FLAG_concurrent_marking) return false;
   base::LockGuard<base::Mutex> guard(&pending_lock_);
-  while (pending_task_count_ > 0) {
-    pending_condition_.Wait(&pending_lock_);
-  }
-}
 
-void ConcurrentMarking::EnsureCompleted() {
-  if (!FLAG_concurrent_marking) return;
-  base::LockGuard<base::Mutex> guard(&pending_lock_);
-  CancelableTaskManager* task_manager =
-      heap_->isolate()->cancelable_task_manager();
-  for (int i = 1; i <= task_count_; i++) {
-    if (is_pending_[i]) {
-      if (task_manager->TryAbort(cancelable_id_[i]) ==
-          CancelableTaskManager::kTaskAborted) {
-        is_pending_[i] = false;
-        --pending_task_count_;
+  if (pending_task_count_ == 0) return false;
+
+  if (stop_request != StopRequest::COMPLETE_TASKS_FOR_TESTING) {
+    CancelableTaskManager* task_manager =
+        heap_->isolate()->cancelable_task_manager();
+    for (int i = 1; i <= task_count_; i++) {
+      if (is_pending_[i]) {
+        if (task_manager->TryAbort(cancelable_id_[i]) ==
+            CancelableTaskManager::kTaskAborted) {
+          is_pending_[i] = false;
+          --pending_task_count_;
+        } else if (stop_request == StopRequest::PREEMPT_TASKS) {
+          task_state_[i].preemption_request.SetValue(true);
+        }
       }
     }
   }
@@ -581,6 +568,7 @@ void ConcurrentMarking::EnsureCompleted() {
   for (int i = 1; i <= task_count_; i++) {
     DCHECK(!is_pending_[i]);
   }
+  return true;
 }
 
 void ConcurrentMarking::FlushLiveBytes(
@@ -620,25 +608,14 @@ size_t ConcurrentMarking::TotalMarkedBytes() {
 }
 
 ConcurrentMarking::PauseScope::PauseScope(ConcurrentMarking* concurrent_marking)
-    : concurrent_marking_(concurrent_marking) {
-  if (!FLAG_concurrent_marking) return;
-  // Request task_state for all tasks.
-  for (int i = 1; i <= kMaxTasks; i++) {
-    concurrent_marking_->task_state_[i].interrupt_request.SetValue(true);
-  }
-  // Now take a lock to ensure that the tasks are waiting.
-  for (int i = 1; i <= kMaxTasks; i++) {
-    concurrent_marking_->task_state_[i].lock.Lock();
-  }
+    : concurrent_marking_(concurrent_marking),
+      resume_on_exit_(concurrent_marking_->Stop(
+          ConcurrentMarking::StopRequest::PREEMPT_TASKS)) {
+  DCHECK_IMPLIES(resume_on_exit_, FLAG_concurrent_marking);
 }
 
 ConcurrentMarking::PauseScope::~PauseScope() {
-  if (!FLAG_concurrent_marking) return;
-  for (int i = kMaxTasks; i >= 1; i--) {
-    concurrent_marking_->task_state_[i].interrupt_request.SetValue(false);
-    concurrent_marking_->task_state_[i].interrupt_condition.NotifyAll();
-    concurrent_marking_->task_state_[i].lock.Unlock();
-  }
+  if (resume_on_exit_) concurrent_marking_->RescheduleTasksIfNeeded();
 }
 
 }  // namespace internal
diff --git a/deps/v8/src/heap/concurrent-marking.h b/deps/v8/src/heap/concurrent-marking.h
index 0f0c8bf992..c5af406e45 100644
--- a/deps/v8/src/heap/concurrent-marking.h
+++ b/deps/v8/src/heap/concurrent-marking.h
@@ -2,10 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_HEAP_CONCURRENT_MARKING_
-#define V8_HEAP_CONCURRENT_MARKING_
+#ifndef V8_HEAP_CONCURRENT_MARKING_H_
+#define V8_HEAP_CONCURRENT_MARKING_H_
 
+#include "include/v8-platform.h"
 #include "src/allocation.h"
+#include "src/base/atomic-utils.h"
+#include "src/base/platform/condition-variable.h"
+#include "src/base/platform/mutex.h"
 #include "src/cancelable-task.h"
 #include "src/heap/spaces.h"
 #include "src/heap/worklist.h"
@@ -26,26 +30,48 @@ using LiveBytesMap =
 class ConcurrentMarking {
  public:
   // When the scope is entered, the concurrent marking tasks
-  // are paused and are not looking at the heap objects.
+  // are preempted and are not looking at the heap objects, concurrent marking
+  // is resumed when the scope is exited.
   class PauseScope {
    public:
     explicit PauseScope(ConcurrentMarking* concurrent_marking);
     ~PauseScope();
 
    private:
-    ConcurrentMarking* concurrent_marking_;
+    ConcurrentMarking* const concurrent_marking_;
+    const bool resume_on_exit_;
   };
 
-  static const int kMaxTasks = 4;
+  enum class StopRequest {
+    // Preempt ongoing tasks ASAP (and cancel unstarted tasks).
+    PREEMPT_TASKS,
+    // Wait for ongoing tasks to complete (and cancels unstarted tasks).
+    COMPLETE_ONGOING_TASKS,
+    // Wait for all scheduled tasks to complete (only use this in tests that
+    // control the full stack -- otherwise tasks cancelled by the platform can
+    // make this call hang).
+    COMPLETE_TASKS_FOR_TESTING,
+  };
+
+  // TODO(gab): The only thing that prevents this being above 7 is
+  // Worklist::kMaxNumTasks being maxed at 8 (concurrent marking doesn't use
+  // task 0, reserved for the main thread).
+  static constexpr int kMaxTasks = 7;
   using MarkingWorklist = Worklist<HeapObject*, 64 /* segment size */>;
 
   ConcurrentMarking(Heap* heap, MarkingWorklist* shared,
                     MarkingWorklist* bailout, MarkingWorklist* on_hold,
                     WeakObjects* weak_objects);
 
+  // Schedules asynchronous tasks to perform concurrent marking. Objects in the
+  // heap should not be moved while these are active (can be stopped safely via
+  // Stop() or PauseScope).
   void ScheduleTasks();
-  void WaitForTasks();
-  void EnsureCompleted();
+
+  // Stops concurrent marking per |stop_request|'s semantics. Returns true
+  // if concurrent marking was in progress, false otherwise.
+  bool Stop(StopRequest stop_request);
+
   void RescheduleTasksIfNeeded();
   // Flushes the local live bytes into the given marking state.
   void FlushLiveBytes(MajorNonAtomicMarkingState* marking_state);
@@ -59,37 +85,32 @@ class ConcurrentMarking {
 
  private:
   struct TaskState {
-    // When the concurrent marking task has this lock, then objects in the
-    // heap are guaranteed to not move.
-    base::Mutex lock;
-    // The main thread sets this flag to true, when it wants the concurrent
-    // maker to give up the lock.
-    base::AtomicValue<bool> interrupt_request;
-    // The concurrent marker waits on this condition until the request
-    // flag is cleared by the main thread.
-    base::ConditionVariable interrupt_condition;
+    // The main thread sets this flag to true when it wants the concurrent
+    // marker to give up the worker thread.
+    base::AtomicValue<bool> preemption_request;
+
     LiveBytesMap live_bytes;
-    size_t marked_bytes;
+    size_t marked_bytes = 0;
     char cache_line_padding[64];
   };
   class Task;
   void Run(int task_id, TaskState* task_state);
-  Heap* heap_;
-  MarkingWorklist* shared_;
-  MarkingWorklist* bailout_;
-  MarkingWorklist* on_hold_;
-  WeakObjects* weak_objects_;
+  Heap* const heap_;
+  MarkingWorklist* const shared_;
+  MarkingWorklist* const bailout_;
+  MarkingWorklist* const on_hold_;
+  WeakObjects* const weak_objects_;
   TaskState task_state_[kMaxTasks + 1];
-  base::AtomicNumber<size_t> total_marked_bytes_;
+  base::AtomicNumber<size_t> total_marked_bytes_{0};
   base::Mutex pending_lock_;
   base::ConditionVariable pending_condition_;
-  int pending_task_count_;
-  bool is_pending_[kMaxTasks + 1];
-  CancelableTaskManager::Id cancelable_id_[kMaxTasks + 1];
-  int task_count_;
+  int pending_task_count_ = 0;
+  bool is_pending_[kMaxTasks + 1] = {};
+  CancelableTaskManager::Id cancelable_id_[kMaxTasks + 1] = {};
+  int task_count_ = 0;
 };
 
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_HEAP_PAGE_PARALLEL_JOB_
+#endif  // V8_HEAP_CONCURRENT_MARKING_H_
diff --git a/deps/v8/src/heap/heap-inl.h b/deps/v8/src/heap/heap-inl.h
index f4e5c1fe13..41af95fa44 100644
--- a/deps/v8/src/heap/heap-inl.h
+++ b/deps/v8/src/heap/heap-inl.h
@@ -626,6 +626,7 @@ CodeSpaceMemoryModificationScope::CodeSpaceMemoryModificationScope(Heap* heap)
     LargePage* page = heap_->lo_space()->first_page();
     while (page != nullptr) {
       if (page->IsFlagSet(MemoryChunk::IS_EXECUTABLE)) {
+        CHECK(heap_->memory_allocator()->IsMemoryChunkExecutable(page));
         page->SetReadAndWritable();
       }
       page = page->next_page();
@@ -640,6 +641,7 @@ CodeSpaceMemoryModificationScope::~CodeSpaceMemoryModificationScope() {
     LargePage* page = heap_->lo_space()->first_page();
     while (page != nullptr) {
       if (page->IsFlagSet(MemoryChunk::IS_EXECUTABLE)) {
+        CHECK(heap_->memory_allocator()->IsMemoryChunkExecutable(page));
         page->SetReadAndExecutable();
       }
       page = page->next_page();
diff --git a/deps/v8/src/heap/heap.cc b/deps/v8/src/heap/heap.cc
index 7f965602b8..9a83c0d172 100644
--- a/deps/v8/src/heap/heap.cc
+++ b/deps/v8/src/heap/heap.cc
@@ -17,7 +17,6 @@
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
-#include "src/compiler-dispatcher/optimizing-compile-dispatcher.h"
 #include "src/conversions.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
@@ -46,6 +45,7 @@
 #include "src/heap/stress-marking-observer.h"
 #include "src/heap/stress-scavenge-observer.h"
 #include "src/heap/sweeper.h"
+#include "src/instruction-stream.h"
 #include "src/interpreter/interpreter.h"
 #include "src/objects/data-handler.h"
 #include "src/objects/shared-function-info.h"
@@ -56,6 +56,7 @@
 #include "src/snapshot/snapshot.h"
 #include "src/tracing/trace-event.h"
 #include "src/trap-handler/trap-handler.h"
+#include "src/unicode-decoder.h"
 #include "src/unicode-inl.h"
 #include "src/utils-inl.h"
 #include "src/utils.h"
@@ -177,6 +178,7 @@ Heap::Heap()
       raw_allocations_hash_(0),
       stress_marking_observer_(nullptr),
       stress_scavenge_observer_(nullptr),
+      allocation_step_in_progress_(false),
       max_marking_limit_reached_(0.0),
       ms_count_(0),
       gc_count_(0),
@@ -461,30 +463,6 @@ bool Heap::IsRetainingPathTarget(HeapObject* object,
   return false;
 }
 
-namespace {
-const char* RootToString(Root root) {
-  switch (root) {
-#define ROOT_CASE(root_id, ignore, description) \
-  case Root::root_id:                           \
-    return description;
-    ROOT_ID_LIST(ROOT_CASE)
-#undef ROOT_CASE
-    case Root::kCodeFlusher:
-      return "(Code flusher)";
-    case Root::kPartialSnapshotCache:
-      return "(Partial snapshot cache)";
-    case Root::kWeakCollections:
-      return "(Weak collections)";
-    case Root::kWrapperTracing:
-      return "(Wrapper tracing)";
-    case Root::kUnknown:
-      return "(Unknown)";
-  }
-  UNREACHABLE();
-  return nullptr;
-}
-}  // namespace
-
 void Heap::PrintRetainingPath(HeapObject* target, RetainingPathOption option) {
   PrintF("\n\n\n");
   PrintF("#################################################\n");
@@ -527,7 +505,7 @@ void Heap::PrintRetainingPath(HeapObject* target, RetainingPathOption option) {
   }
   PrintF("\n");
   PrintF("^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n");
-  PrintF("Root: %s\n", RootToString(root));
+  PrintF("Root: %s\n", RootVisitor::RootName(root));
   PrintF("-------------------------------------------------\n");
 }
 
@@ -644,7 +622,7 @@ const char* Heap::GetSpaceName(int idx) {
   return nullptr;
 }
 
-void Heap::SetRootCodeStubs(NumberDictionary* value) {
+void Heap::SetRootCodeStubs(SimpleNumberDictionary* value) {
   roots_[kCodeStubsRootIndex] = value;
 }
 
@@ -1112,6 +1090,66 @@ void Heap::CollectAllGarbage(int flags, GarbageCollectionReason gc_reason,
   set_current_gc_flags(kNoGCFlags);
 }
 
+namespace {
+
+intptr_t CompareWords(int size, HeapObject* a, HeapObject* b) {
+  int words = size / kPointerSize;
+  DCHECK_EQ(a->Size(), size);
+  DCHECK_EQ(b->Size(), size);
+  intptr_t* slot_a = reinterpret_cast<intptr_t*>(a->address());
+  intptr_t* slot_b = reinterpret_cast<intptr_t*>(b->address());
+  for (int i = 0; i < words; i++) {
+    if (*slot_a != *slot_b) {
+      return *slot_a - *slot_b;
+    }
+    slot_a++;
+    slot_b++;
+  }
+  return 0;
+}
+
+void ReportDuplicates(int size, std::vector<HeapObject*>& objects) {
+  if (objects.size() == 0) return;
+
+  sort(objects.begin(), objects.end(), [size](HeapObject* a, HeapObject* b) {
+    intptr_t c = CompareWords(size, a, b);
+    if (c != 0) return c < 0;
+    return a < b;
+  });
+
+  std::vector<std::pair<int, HeapObject*>> duplicates;
+  HeapObject* current = objects[0];
+  int count = 1;
+  for (size_t i = 1; i < objects.size(); i++) {
+    if (CompareWords(size, current, objects[i]) == 0) {
+      count++;
+    } else {
+      if (count > 1) {
+        duplicates.push_back(std::make_pair(count - 1, current));
+      }
+      count = 1;
+      current = objects[i];
+    }
+  }
+  if (count > 1) {
+    duplicates.push_back(std::make_pair(count - 1, current));
+  }
+
+  int threshold = FLAG_trace_duplicate_threshold_kb * KB;
+
+  sort(duplicates.begin(), duplicates.end());
+  for (auto it = duplicates.rbegin(); it != duplicates.rend(); ++it) {
+    int duplicate_bytes = it->first * size;
+    if (duplicate_bytes < threshold) break;
+    PrintF("%d duplicates of size %d each (%dKB)\n", it->first, size,
+           duplicate_bytes / KB);
+    PrintF("Sample object: ");
+    it->second->Print();
+    PrintF("============================\n");
+  }
+}
+}  // anonymous namespace
+
 void Heap::CollectAllAvailableGarbage(GarbageCollectionReason gc_reason) {
   // Since we are ignoring the return value, the exact choice of space does
   // not matter, so long as we do not specify NEW_SPACE, which would not
@@ -1129,12 +1167,9 @@ void Heap::CollectAllAvailableGarbage(GarbageCollectionReason gc_reason) {
   }
   RuntimeCallTimerScope runtime_timer(
       isolate(), RuntimeCallCounterId::kGC_Custom_AllAvailableGarbage);
-  if (isolate()->concurrent_recompilation_enabled()) {
-    // The optimizing compiler may be unnecessarily holding on to memory.
-    DisallowHeapAllocation no_recursive_gc;
-    isolate()->optimizing_compile_dispatcher()->Flush(
-        OptimizingCompileDispatcher::BlockingBehavior::kDontBlock);
-  }
+
+  // The optimizing compiler may be unnecessarily holding on to memory.
+  isolate()->AbortConcurrentOptimization(BlockingBehavior::kDontBlock);
   isolate()->ClearSerializerData();
   set_current_gc_flags(kMakeHeapIterableMask | kReduceMemoryFootprintMask);
   isolate_->compilation_cache()->Clear();
@@ -1151,6 +1186,28 @@ void Heap::CollectAllAvailableGarbage(GarbageCollectionReason gc_reason) {
   set_current_gc_flags(kNoGCFlags);
   new_space_->Shrink();
   UncommitFromSpace();
+
+  if (FLAG_trace_duplicate_threshold_kb) {
+    std::map<int, std::vector<HeapObject*>> objects_by_size;
+    PagedSpaces spaces(this);
+    for (PagedSpace* space = spaces.next(); space != nullptr;
+         space = spaces.next()) {
+      HeapObjectIterator it(space);
+      for (HeapObject* obj = it.Next(); obj != nullptr; obj = it.Next()) {
+        objects_by_size[obj->Size()].push_back(obj);
+      }
+    }
+    {
+      LargeObjectIterator it(lo_space());
+      for (HeapObject* obj = it.Next(); obj != nullptr; obj = it.Next()) {
+        objects_by_size[obj->Size()].push_back(obj);
+      }
+    }
+    for (auto it = objects_by_size.rbegin(); it != objects_by_size.rend();
+         ++it) {
+      ReportDuplicates(it->first, it->second);
+    }
+  }
 }
 
 void Heap::ReportExternalMemoryPressure() {
@@ -1316,11 +1373,8 @@ int Heap::NotifyContextDisposed(bool dependant_context) {
     event.time_ms = MonotonicallyIncreasingTimeInMs();
     memory_reducer_->NotifyPossibleGarbage(event);
   }
-  if (isolate()->concurrent_recompilation_enabled()) {
-    // Flush the queued recompilation tasks.
-    isolate()->optimizing_compile_dispatcher()->Flush(
-        OptimizingCompileDispatcher::BlockingBehavior::kDontBlock);
-  }
+  isolate()->AbortConcurrentOptimization(BlockingBehavior::kDontBlock);
+
   number_of_disposed_maps_ = retained_maps()->Length();
   tracer()->AddContextDisposalTime(MonotonicallyIncreasingTimeInMs());
   return ++contexts_disposed_;
@@ -1733,12 +1787,12 @@ void Heap::MarkCompact() {
 void Heap::MinorMarkCompact() {
   DCHECK(FLAG_minor_mc);
 
+  PauseAllocationObserversScope pause_observers(this);
   SetGCState(MINOR_MARK_COMPACT);
   LOG(isolate_, ResourceEvent("MinorMarkCompact", "begin"));
 
   TRACE_GC(tracer(), GCTracer::Scope::MINOR_MC);
   AlwaysAllocateScope always_allocate(isolate());
-  PauseAllocationObserversScope pause_observers(this);
   IncrementalMarking::PauseBlackAllocationScope pause_black_allocation(
       incremental_marking());
   CodeSpaceMemoryModificationScope code_modifcation(this);
@@ -1924,11 +1978,10 @@ int Heap::NumberOfScavengeTasks() {
   if (!FLAG_parallel_scavenge) return 1;
   const int num_scavenge_tasks =
       static_cast<int>(new_space()->TotalCapacity()) / MB;
-  return Max(
-      1,
-      Min(Min(num_scavenge_tasks, kMaxScavengerTasks),
-          static_cast<int>(
-              V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads())));
+  static int num_cores =
+      1 + static_cast<int>(
+              V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads());
+  return Max(1, Min(Min(num_scavenge_tasks, kMaxScavengerTasks), num_cores));
 }
 
 void Heap::Scavenge() {
@@ -2015,7 +2068,7 @@ void Heap::Scavenge() {
     {
       // Parallel phase scavenging all copied and promoted objects.
       TRACE_GC(tracer(), GCTracer::Scope::SCAVENGER_SCAVENGE_PARALLEL);
-      job.Run();
+      job.Run(isolate()->async_counters());
       DCHECK(copied_list.IsGlobalEmpty());
       DCHECK(promotion_list.IsGlobalEmpty());
     }
@@ -2187,7 +2240,8 @@ void Heap::ExternalStringTable::PromoteAllNewSpaceStrings() {
 
 void Heap::ExternalStringTable::IterateNewSpaceStrings(RootVisitor* v) {
   if (!new_space_strings_.empty()) {
-    v->VisitRootPointers(Root::kExternalStringsTable, new_space_strings_.data(),
+    v->VisitRootPointers(Root::kExternalStringsTable, nullptr,
+                         new_space_strings_.data(),
                          new_space_strings_.data() + new_space_strings_.size());
   }
 }
@@ -2195,7 +2249,8 @@ void Heap::ExternalStringTable::IterateNewSpaceStrings(RootVisitor* v) {
 void Heap::ExternalStringTable::IterateAll(RootVisitor* v) {
   IterateNewSpaceStrings(v);
   if (!old_space_strings_.empty()) {
-    v->VisitRootPointers(Root::kExternalStringsTable, old_space_strings_.data(),
+    v->VisitRootPointers(Root::kExternalStringsTable, nullptr,
+                         old_space_strings_.data(),
                          old_space_strings_.data() + old_space_strings_.size());
   }
 }
@@ -2301,7 +2356,8 @@ void Heap::VisitExternalResources(v8::ExternalResourceVisitor* visitor) {
     explicit ExternalStringTableVisitorAdapter(
         v8::ExternalResourceVisitor* visitor)
         : visitor_(visitor) {}
-    virtual void VisitRootPointers(Root root, Object** start, Object** end) {
+    virtual void VisitRootPointers(Root root, const char* description,
+                                   Object** start, Object** end) {
       for (Object** p = start; p < end; p++) {
         DCHECK((*p)->IsExternalString());
         visitor_->VisitExternalString(
@@ -2512,12 +2568,12 @@ AllocationResult Heap::AllocateHeapNumber(MutableMode mode,
   return result;
 }
 
-AllocationResult Heap::AllocateBigInt(int length) {
+AllocationResult Heap::AllocateBigInt(int length, PretenureFlag pretenure) {
   if (length < 0 || length > BigInt::kMaxLength) {
     v8::internal::Heap::FatalProcessOutOfMemory("invalid BigInt length", true);
   }
   int size = BigInt::SizeFor(length);
-  AllocationSpace space = SelectSpace(NOT_TENURED);
+  AllocationSpace space = SelectSpace(pretenure);
   HeapObject* result = nullptr;
   {
     AllocationResult allocation = AllocateRaw(size, space);
@@ -2541,6 +2597,20 @@ AllocationResult Heap::AllocateCell(Object* value) {
   return result;
 }
 
+AllocationResult Heap::AllocateFeedbackCell(Map* map, HeapObject* value) {
+  int size = FeedbackCell::kSize;
+  STATIC_ASSERT(FeedbackCell::kSize <= kMaxRegularHeapObjectSize);
+
+  HeapObject* result = nullptr;
+  {
+    AllocationResult allocation = AllocateRaw(size, OLD_SPACE);
+    if (!allocation.To(&result)) return allocation;
+  }
+  result->set_map_after_allocation(map, SKIP_WRITE_BARRIER);
+  FeedbackCell::cast(result)->set_value(value);
+  return result;
+}
+
 AllocationResult Heap::AllocatePropertyCell(Name* name) {
   DCHECK(name->IsUniqueName());
   int size = PropertyCell::kSize;
@@ -2849,11 +2919,11 @@ AllocationResult Heap::AllocateBytecodeArray(int length,
   instance->set_parameter_count(parameter_count);
   instance->set_incoming_new_target_or_generator_register(
       interpreter::Register::invalid_value());
-  instance->set_interrupt_budget(interpreter::Interpreter::kInterruptBudget);
+  instance->set_interrupt_budget(interpreter::Interpreter::InterruptBudget());
   instance->set_osr_loop_nesting_level(0);
   instance->set_bytecode_age(BytecodeArray::kNoAgeBytecodeAge);
   instance->set_constant_pool(constant_pool);
-  instance->set_handler_table(empty_fixed_array());
+  instance->set_handler_table(empty_byte_array());
   instance->set_source_position_table(empty_byte_array());
   CopyBytes(instance->GetFirstBytecodeAddress(), raw_bytecodes, length);
   instance->clear_padding();
@@ -3145,10 +3215,10 @@ AllocationResult Heap::AllocateCode(int object_size, Movability movability) {
 AllocationResult Heap::AllocateCode(
     const CodeDesc& desc, Code::Kind kind, Handle<Object> self_ref,
     int32_t builtin_index, ByteArray* reloc_info,
-    CodeDataContainer* data_container, HandlerTable* handler_table,
-    ByteArray* source_position_table, DeoptimizationData* deopt_data,
-    Movability movability, uint32_t stub_key, bool is_turbofanned,
-    int stack_slots, int safepoint_table_offset) {
+    CodeDataContainer* data_container, ByteArray* source_position_table,
+    DeoptimizationData* deopt_data, Movability movability, uint32_t stub_key,
+    bool is_turbofanned, int stack_slots, int safepoint_table_offset,
+    int handler_table_offset) {
   bool has_unwinding_info = desc.unwinding_info != nullptr;
   DCHECK((has_unwinding_info && desc.unwinding_info_size > 0) ||
          (!has_unwinding_info && desc.unwinding_info_size == 0));
@@ -3174,11 +3244,11 @@ AllocationResult Heap::AllocateCode(
   code->set_relocation_info(reloc_info);
   code->initialize_flags(kind, has_unwinding_info, is_turbofanned, stack_slots);
   code->set_safepoint_table_offset(safepoint_table_offset);
+  code->set_handler_table_offset(handler_table_offset);
   code->set_code_data_container(data_container);
   code->set_has_tagged_params(true);
   code->set_deoptimization_data(deopt_data);
   code->set_stub_key(stub_key);
-  code->set_handler_table(handler_table);
   code->set_source_position_table(source_position_table);
   code->set_protected_instructions(empty_fixed_array(), SKIP_WRITE_BARRIER);
   code->set_constant_pool_offset(desc.instr_size - desc.constant_pool_size);
@@ -3322,6 +3392,21 @@ AllocationResult Heap::Allocate(Map* map, AllocationSpace space,
   return result;
 }
 
+AllocationResult Heap::AllocateJSPromise(JSFunction* constructor,
+                                         PretenureFlag pretenure) {
+  AllocationResult allocation = AllocateJSObject(constructor, pretenure);
+  JSPromise* promise = nullptr;
+  if (!allocation.To(&promise)) return allocation;
+
+  // Setup JSPromise fields
+  promise->set_reactions_or_result(Smi::kZero);
+  promise->set_flags(0);
+  for (int i = 0; i < v8::Promise::kEmbedderFieldCount; i++) {
+    promise->SetEmbedderField(i, Smi::kZero);
+  }
+  return promise;
+}
+
 void Heap::InitializeJSObjectFromMap(JSObject* obj, Object* properties,
                                      Map* map) {
   obj->set_raw_properties_or_hash(properties);
@@ -3503,28 +3588,17 @@ static inline void WriteOneByteData(Vector<const char> vector, uint8_t* chars,
 
 static inline void WriteTwoByteData(Vector<const char> vector, uint16_t* chars,
                                     int len) {
-  const uint8_t* stream = reinterpret_cast<const uint8_t*>(vector.start());
-  size_t stream_length = vector.length();
-  while (stream_length != 0) {
-    size_t consumed = 0;
-    uint32_t c = unibrow::Utf8::ValueOf(stream, stream_length, &consumed);
+  unibrow::Utf8Iterator it = unibrow::Utf8Iterator(vector);
+  while (!it.Done()) {
+    DCHECK_GT(len, 0);
+    len -= 1;
+
+    uint16_t c = *it;
+    ++it;
     DCHECK_NE(unibrow::Utf8::kBadChar, c);
-    DCHECK(consumed <= stream_length);
-    stream_length -= consumed;
-    stream += consumed;
-    if (c > unibrow::Utf16::kMaxNonSurrogateCharCode) {
-      len -= 2;
-      if (len < 0) break;
-      *chars++ = unibrow::Utf16::LeadSurrogate(c);
-      *chars++ = unibrow::Utf16::TrailSurrogate(c);
-    } else {
-      len -= 1;
-      if (len < 0) break;
-      *chars++ = c;
-    }
+    *chars++ = c;
   }
-  DCHECK_EQ(0, stream_length);
-  DCHECK_EQ(0, len);
+  DCHECK_EQ(len, 0);
 }
 
 
@@ -4447,12 +4521,8 @@ class MemoryPressureInterruptTask : public CancelableTask {
 
 void Heap::CheckMemoryPressure() {
   if (HighMemoryPressure()) {
-    if (isolate()->concurrent_recompilation_enabled()) {
-      // The optimizing compiler may be unnecessarily holding on to memory.
-      DisallowHeapAllocation no_recursive_gc;
-      isolate()->optimizing_compile_dispatcher()->Flush(
-          OptimizingCompileDispatcher::BlockingBehavior::kDontBlock);
-    }
+    // The optimizing compiler may be unnecessarily holding on to memory.
+    isolate()->AbortConcurrentOptimization(BlockingBehavior::kDontBlock);
   }
   if (memory_pressure_level_.Value() == MemoryPressureLevel::kCritical) {
     CollectGarbageOnMemoryPressure();
@@ -4877,8 +4947,9 @@ void Heap::IterateWeakRoots(RootVisitor* v, VisitMode mode) {
   const bool isMinorGC = mode == VISIT_ALL_IN_SCAVENGE ||
                          mode == VISIT_ALL_IN_MINOR_MC_MARK ||
                          mode == VISIT_ALL_IN_MINOR_MC_UPDATE;
-  v->VisitRootPointer(Root::kStringTable, reinterpret_cast<Object**>(
-                                              &roots_[kStringTableRootIndex]));
+  v->VisitRootPointer(
+      Root::kStringTable, nullptr,
+      reinterpret_cast<Object**>(&roots_[kStringTableRootIndex]));
   v->Synchronize(VisitorSynchronization::kStringTable);
   if (!isMinorGC && mode != VISIT_ALL_IN_SWEEP_NEWSPACE &&
       mode != VISIT_FOR_SERIALIZATION) {
@@ -4893,13 +4964,13 @@ void Heap::IterateWeakRoots(RootVisitor* v, VisitMode mode) {
 void Heap::IterateSmiRoots(RootVisitor* v) {
   // Acquire execution access since we are going to read stack limit values.
   ExecutionAccess access(isolate());
-  v->VisitRootPointers(Root::kSmiRootList, &roots_[kSmiRootsStart],
+  v->VisitRootPointers(Root::kSmiRootList, nullptr, &roots_[kSmiRootsStart],
                        &roots_[kRootListLength]);
   v->Synchronize(VisitorSynchronization::kSmiRootList);
 }
 
 void Heap::IterateEncounteredWeakCollections(RootVisitor* visitor) {
-  visitor->VisitRootPointer(Root::kWeakCollections,
+  visitor->VisitRootPointer(Root::kWeakCollections, nullptr,
                             &encountered_weak_collections_);
 }
 
@@ -4913,9 +4984,13 @@ class FixStaleLeftTrimmedHandlesVisitor : public RootVisitor {
     USE(heap_);
   }
 
-  void VisitRootPointer(Root root, Object** p) override { FixHandle(p); }
+  void VisitRootPointer(Root root, const char* description,
+                        Object** p) override {
+    FixHandle(p);
+  }
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     for (Object** p = start; p < end; p++) FixHandle(p);
   }
 
@@ -4951,7 +5026,7 @@ void Heap::IterateStrongRoots(RootVisitor* v, VisitMode mode) {
   const bool isMinorGC = mode == VISIT_ALL_IN_SCAVENGE ||
                          mode == VISIT_ALL_IN_MINOR_MC_MARK ||
                          mode == VISIT_ALL_IN_MINOR_MC_UPDATE;
-  v->VisitRootPointers(Root::kStrongRootList, &roots_[0],
+  v->VisitRootPointers(Root::kStrongRootList, nullptr, &roots_[0],
                        &roots_[kStrongRootListLength]);
   v->Synchronize(VisitorSynchronization::kStrongRootList);
 
@@ -5026,7 +5101,7 @@ void Heap::IterateStrongRoots(RootVisitor* v, VisitMode mode) {
 
   // Iterate over other strong roots (currently only identity maps).
   for (StrongRootsList* list = strong_roots_list_; list; list = list->next) {
-    v->VisitRootPointers(Root::kStrongRoots, list->start, list->end);
+    v->VisitRootPointers(Root::kStrongRoots, nullptr, list->start, list->end);
   }
   v->Synchronize(VisitorSynchronization::kStrongRoots);
 
@@ -5038,6 +5113,9 @@ void Heap::IterateStrongRoots(RootVisitor* v, VisitMode mode) {
   }
 }
 
+void Heap::IterateWeakGlobalHandles(RootVisitor* v) {
+  isolate_->global_handles()->IterateWeakRoots(v);
+}
 
 // TODO(1236194): Since the heap size is configurable on the command line
 // and through the API, we should gracefully handle the case that the heap
@@ -5745,7 +5823,8 @@ void Heap::RegisterExternallyReferencedObject(Object** object) {
 }
 
 void Heap::TearDown() {
-  use_tasks_ = false;
+  SetGCState(TEAR_DOWN);
+  DCHECK(!use_tasks_);
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     Verify();
@@ -6035,7 +6114,8 @@ void Heap::FatalProcessOutOfMemory(const char* location, bool is_heap_oom) {
 
 class PrintHandleVisitor : public RootVisitor {
  public:
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     for (Object** p = start; p < end; p++)
       PrintF("  handle %p to %p\n", reinterpret_cast<void*>(p),
              reinterpret_cast<void*>(*p));
@@ -6057,7 +6137,8 @@ class CheckHandleCountVisitor : public RootVisitor {
   ~CheckHandleCountVisitor() override {
     CHECK_GT(HandleScope::kCheckHandleThreshold, handle_count_);
   }
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     handle_count_ += end - start;
   }
 
@@ -6207,7 +6288,8 @@ class UnreachableObjectsFilter : public HeapObjectsFilter {
       MarkPointers(start, end);
     }
 
-    void VisitRootPointers(Root root, Object** start, Object** end) override {
+    void VisitRootPointers(Root root, const char* description, Object** start,
+                           Object** end) override {
       MarkPointers(start, end);
     }
 
@@ -6449,6 +6531,10 @@ void Heap::SetDeserializeLazyHandlerExtraWide(Code* code) {
   set_deserialize_lazy_handler_extra_wide(code);
 }
 
+void Heap::SetBuiltinsConstantsTable(FixedArray* cache) {
+  set_builtins_constants_table(cache);
+}
+
 size_t Heap::NumberOfTrackedHeapObjectTypes() {
   return ObjectStats::OBJECT_STATS_COUNT;
 }
@@ -6480,19 +6566,13 @@ bool Heap::GetObjectTypeName(size_t index, const char** object_type,
     return true;
     INSTANCE_TYPE_LIST(COMPARE_AND_RETURN_NAME)
 #undef COMPARE_AND_RETURN_NAME
-#define COMPARE_AND_RETURN_NAME(name)                      \
-  case ObjectStats::FIRST_CODE_KIND_SUB_TYPE + Code::name: \
-    *object_type = "CODE_TYPE";                            \
-    *object_sub_type = "CODE_KIND/" #name;                 \
-    return true;
-    CODE_KIND_LIST(COMPARE_AND_RETURN_NAME)
-#undef COMPARE_AND_RETURN_NAME
-#define COMPARE_AND_RETURN_NAME(name)                  \
-  case ObjectStats::FIRST_FIXED_ARRAY_SUB_TYPE + name: \
-    *object_type = "FIXED_ARRAY_TYPE";                 \
-    *object_sub_type = #name;                          \
+
+#define COMPARE_AND_RETURN_NAME(name)                       \
+  case ObjectStats::FIRST_VIRTUAL_TYPE + ObjectStats::name: \
+    *object_type = #name;                                   \
+    *object_sub_type = "";                                  \
     return true;
-    FIXED_ARRAY_SUB_INSTANCE_TYPE_LIST(COMPARE_AND_RETURN_NAME)
+    VIRTUAL_INSTANCE_TYPE_LIST(COMPARE_AND_RETURN_NAME)
 #undef COMPARE_AND_RETURN_NAME
   }
   return false;
@@ -6537,8 +6617,9 @@ void VerifyPointersVisitor::VisitPointers(HeapObject* host, Object** start,
   VerifyPointers(start, end);
 }
 
-void VerifyPointersVisitor::VisitRootPointers(Root root, Object** start,
-                                              Object** end) {
+void VerifyPointersVisitor::VisitRootPointers(Root root,
+                                              const char* description,
+                                              Object** start, Object** end) {
   VerifyPointers(start, end);
 }
 
@@ -6554,8 +6635,8 @@ void VerifyPointersVisitor::VerifyPointers(Object** start, Object** end) {
   }
 }
 
-void VerifySmisVisitor::VisitRootPointers(Root root, Object** start,
-                                          Object** end) {
+void VerifySmisVisitor::VisitRootPointers(Root root, const char* description,
+                                          Object** start, Object** end) {
   for (Object** current = start; current < end; current++) {
     CHECK((*current)->IsSmi());
   }
@@ -6580,12 +6661,11 @@ bool Heap::AllowedToBeMigrated(HeapObject* obj, AllocationSpace dst) {
   AllocationSpace src = chunk->owner()->identity();
   switch (src) {
     case NEW_SPACE:
-      return dst == src || dst == OLD_SPACE;
+      return dst == NEW_SPACE || dst == OLD_SPACE;
     case OLD_SPACE:
-      return dst == src &&
-             (dst == OLD_SPACE || obj->IsFiller() || obj->IsExternalString());
+      return dst == OLD_SPACE;
     case CODE_SPACE:
-      return dst == src && type == CODE_TYPE;
+      return dst == CODE_SPACE && type == CODE_TYPE;
     case MAP_SPACE:
     case LO_SPACE:
       return false;
@@ -6612,6 +6692,7 @@ void AllocationObserver::AllocationStep(int bytes_allocated,
     step_size_ = GetNextStepSize();
     bytes_to_next_step_ = step_size_;
   }
+  DCHECK_GE(bytes_to_next_step_, 0);
 }
 
 namespace {
@@ -6638,12 +6719,24 @@ Code* GcSafeCastToCode(Heap* heap, HeapObject* object, Address inner_pointer) {
 bool Heap::GcSafeCodeContains(HeapObject* code, Address addr) {
   Map* map = GcSafeMapOfCodeSpaceObject(code);
   DCHECK(map == code->GetHeap()->code_map());
+#ifdef V8_EMBEDDED_BUILTINS
+  if (FLAG_stress_off_heap_code) {
+    if (InstructionStream::TryLookupCode(isolate(), addr) == code) return true;
+  }
+#endif
   Address start = code->address();
   Address end = code->address() + code->SizeFromMap(map);
   return start <= addr && addr < end;
 }
 
 Code* Heap::GcSafeFindCodeForInnerPointer(Address inner_pointer) {
+#ifdef V8_EMBEDDED_BUILTINS
+  if (FLAG_stress_off_heap_code) {
+    Code* code = InstructionStream::TryLookupCode(isolate(), inner_pointer);
+    if (code != nullptr) return code;
+  }
+#endif
+
   // Check if the inner pointer points into a large object chunk.
   LargePage* large_page = lo_space()->FindPage(inner_pointer);
   if (large_page != nullptr) {
diff --git a/deps/v8/src/heap/heap.h b/deps/v8/src/heap/heap.h
index 7cc65479ca..63bcfb2990 100644
--- a/deps/v8/src/heap/heap.h
+++ b/deps/v8/src/heap/heap.h
@@ -114,6 +114,7 @@ using v8::MemoryPressureLevel;
   V(Map, name_dictionary_map, NameDictionaryMap)                               \
   V(Map, global_dictionary_map, GlobalDictionaryMap)                           \
   V(Map, number_dictionary_map, NumberDictionaryMap)                           \
+  V(Map, simple_number_dictionary_map, SimpleNumberDictionaryMap)              \
   V(Map, string_table_map, StringTableMap)                                     \
   V(Map, weak_hash_table_map, WeakHashTableMap)                                \
   V(Map, sloppy_arguments_elements_map, SloppyArgumentsElementsMap)            \
@@ -168,6 +169,8 @@ using v8::MemoryPressureLevel;
   V(Map, fixed_float32_array_map, FixedFloat32ArrayMap)                        \
   V(Map, fixed_float64_array_map, FixedFloat64ArrayMap)                        \
   V(Map, fixed_uint8_clamped_array_map, FixedUint8ClampedArrayMap)             \
+  V(Map, fixed_biguint64_array_map, FixedBigUint64ArrayMap)                    \
+  V(Map, fixed_bigint64_array_map, FixedBigInt64ArrayMap)                      \
   /* Oddball maps */                                                           \
   V(Map, undefined_map, UndefinedMap)                                          \
   V(Map, the_hole_map, TheHoleMap)                                             \
@@ -193,8 +196,11 @@ using v8::MemoryPressureLevel;
   V(FixedTypedArrayBase, empty_fixed_float64_array, EmptyFixedFloat64Array)    \
   V(FixedTypedArrayBase, empty_fixed_uint8_clamped_array,                      \
     EmptyFixedUint8ClampedArray)                                               \
+  V(FixedTypedArrayBase, empty_fixed_biguint64_array,                          \
+    EmptyFixedBigUint64Array)                                                  \
+  V(FixedTypedArrayBase, empty_fixed_bigint64_array, EmptyFixedBigInt64Array)  \
   V(Script, empty_script, EmptyScript)                                         \
-  V(Cell, undefined_cell, UndefinedCell)                                       \
+  V(FeedbackCell, many_closures_cell, ManyClosuresCell)                        \
   V(FixedArray, empty_sloppy_arguments_elements, EmptySloppyArgumentsElements) \
   V(NumberDictionary, empty_slow_element_dictionary,                           \
     EmptySlowElementDictionary)                                                \
@@ -213,6 +219,8 @@ using v8::MemoryPressureLevel;
   V(PropertyCell, array_iterator_protector, ArrayIteratorProtector)            \
   V(PropertyCell, array_buffer_neutering_protector,                            \
     ArrayBufferNeuteringProtector)                                             \
+  V(PropertyCell, promise_hook_protector, PromiseHookProtector)                \
+  V(PropertyCell, promise_then_protector, PromiseThenProtector)                \
   /* Special numbers */                                                        \
   V(HeapNumber, nan_value, NanValue)                                           \
   V(HeapNumber, hole_nan_value, HoleNanValue)                                  \
@@ -230,7 +238,7 @@ using v8::MemoryPressureLevel;
   V(NameDictionary, api_symbol_table, ApiSymbolTable)                          \
   V(NameDictionary, api_private_symbol_table, ApiPrivateSymbolTable)           \
   V(Object, script_list, ScriptList)                                           \
-  V(NumberDictionary, code_stubs, CodeStubs)                                   \
+  V(SimpleNumberDictionary, code_stubs, CodeStubs)                             \
   V(FixedArray, materialized_objects, MaterializedObjects)                     \
   V(FixedArray, microtask_queue, MicrotaskQueue)                               \
   V(FixedArray, detached_contexts, DetachedContexts)                           \
@@ -242,6 +250,8 @@ using v8::MemoryPressureLevel;
   /* slots refer to the code with the reference to the weak object. */         \
   V(ArrayList, weak_new_space_object_to_code_list,                             \
     WeakNewSpaceObjectToCodeList)                                              \
+  /* Indirection lists for isolate-independent builtins */                     \
+  V(FixedArray, builtins_constants_table, BuiltinsConstantsTable)              \
   /* Feedback vectors that we need for code coverage or type profile */        \
   V(Object, feedback_vectors_for_profiling_tools,                              \
     FeedbackVectorsForProfilingTools)                                          \
@@ -340,6 +350,7 @@ using v8::MemoryPressureLevel;
   V(JsConstructEntryCode)               \
   V(JsEntryCode)                        \
   V(JSMessageObjectMap)                 \
+  V(ManyClosuresCell)                   \
   V(ManyClosuresCellMap)                \
   V(MetaMap)                            \
   V(MinusInfinityValue)                 \
@@ -363,6 +374,7 @@ using v8::MemoryPressureLevel;
   V(ScopeInfoMap)                       \
   V(ScriptContextMap)                   \
   V(SharedFunctionInfoMap)              \
+  V(SimpleNumberDictionaryMap)          \
   V(SloppyArgumentsElementsMap)         \
   V(SmallOrderedHashMapMap)             \
   V(SmallOrderedHashSetMap)             \
@@ -377,7 +389,6 @@ using v8::MemoryPressureLevel;
   V(TransitionArrayMap)                 \
   V(TrueValue)                          \
   V(TwoPointerFillerMap)                \
-  V(UndefinedCell)                      \
   V(UndefinedMap)                       \
   V(UndefinedValue)                     \
   V(UninitializedMap)                   \
@@ -575,7 +586,13 @@ class Heap {
 
   enum FindMementoMode { kForRuntime, kForGC };
 
-  enum HeapState { NOT_IN_GC, SCAVENGE, MARK_COMPACT, MINOR_MARK_COMPACT };
+  enum HeapState {
+    NOT_IN_GC,
+    SCAVENGE,
+    MARK_COMPACT,
+    MINOR_MARK_COMPACT,
+    TEAR_DOWN
+  };
 
   using PretenuringFeedbackMap = std::unordered_map<AllocationSite*, size_t>;
 
@@ -966,6 +983,8 @@ class Heap {
   // Returns whether SetUp has been called.
   bool HasBeenSetUp();
 
+  void stop_using_tasks() { use_tasks_ = false; }
+
   bool use_tasks() const { return use_tasks_; }
 
   // ===========================================================================
@@ -1062,7 +1081,7 @@ class Heap {
   Object** roots_array_start() { return roots_; }
 
   // Sets the stub_cache_ (only used when expanding the dictionary).
-  void SetRootCodeStubs(NumberDictionary* value);
+  void SetRootCodeStubs(SimpleNumberDictionary* value);
 
   void SetRootMaterializedObjects(FixedArray* objects) {
     roots_[kMaterializedObjectsRootIndex] = objects;
@@ -1110,6 +1129,8 @@ class Heap {
   void SetDeserializeLazyHandlerWide(Code* code);
   void SetDeserializeLazyHandlerExtraWide(Code* code);
 
+  void SetBuiltinsConstantsTable(FixedArray* cache);
+
   // ===========================================================================
   // Inline allocation. ========================================================
   // ===========================================================================
@@ -1161,15 +1182,15 @@ class Heap {
   // Iterators. ================================================================
   // ===========================================================================
 
-  // Iterates over all roots in the heap.
   void IterateRoots(RootVisitor* v, VisitMode mode);
-  // Iterates over all strong roots in the heap.
   void IterateStrongRoots(RootVisitor* v, VisitMode mode);
   // Iterates over entries in the smi roots list.  Only interesting to the
   // serializer/deserializer, since GC does not care about smis.
   void IterateSmiRoots(RootVisitor* v);
-  // Iterates over all the other roots in the heap.
+  // Iterates over weak string tables.
   void IterateWeakRoots(RootVisitor* v, VisitMode mode);
+  // Iterates over weak global handles.
+  void IterateWeakGlobalHandles(RootVisitor* v);
 
   // ===========================================================================
   // Store buffer API. =========================================================
@@ -1571,6 +1592,11 @@ class Heap {
   void RemoveAllocationObserversFromAllSpaces(
       AllocationObserver* observer, AllocationObserver* new_space_observer);
 
+  bool allocation_step_in_progress() { return allocation_step_in_progress_; }
+  void set_allocation_step_in_progress(bool val) {
+    allocation_step_in_progress_ = val;
+  }
+
   // ===========================================================================
   // Retaining path tracking. ==================================================
   // ===========================================================================
@@ -2076,7 +2102,8 @@ class Heap {
   MUST_USE_RESULT AllocationResult AllocateHeapNumber(
       MutableMode mode = IMMUTABLE, PretenureFlag pretenure = NOT_TENURED);
 
-  MUST_USE_RESULT AllocationResult AllocateBigInt(int length);
+  MUST_USE_RESULT AllocationResult
+  AllocateBigInt(int length, PretenureFlag pretenure = NOT_TENURED);
 
   // Allocates a byte array of the specified length
   MUST_USE_RESULT AllocationResult
@@ -2265,6 +2292,10 @@ class Heap {
   // Allocate a tenured simple cell.
   MUST_USE_RESULT AllocationResult AllocateCell(Object* value);
 
+  // Allocate a tenured simple feedback cell.
+  MUST_USE_RESULT AllocationResult AllocateFeedbackCell(Map* map,
+                                                        HeapObject* value);
+
   // Allocate a tenured JS global property cell initialized with the hole.
   MUST_USE_RESULT AllocationResult AllocatePropertyCell(Name* name);
 
@@ -2287,13 +2318,16 @@ class Heap {
 
   // Allocates a new code object (fully initialized). All header fields of the
   // returned object are immutable and the code object is write protected.
-  MUST_USE_RESULT AllocationResult
-  AllocateCode(const CodeDesc& desc, Code::Kind kind, Handle<Object> self_ref,
-               int32_t builtin_index, ByteArray* reloc_info,
-               CodeDataContainer* data_container, HandlerTable* handler_table,
-               ByteArray* source_position_table, DeoptimizationData* deopt_data,
-               Movability movability, uint32_t stub_key, bool is_turbofanned,
-               int stack_slots, int safepoint_table_offset);
+  MUST_USE_RESULT AllocationResult AllocateCode(
+      const CodeDesc& desc, Code::Kind kind, Handle<Object> self_ref,
+      int32_t builtin_index, ByteArray* reloc_info,
+      CodeDataContainer* data_container, ByteArray* source_position_table,
+      DeoptimizationData* deopt_data, Movability movability, uint32_t stub_key,
+      bool is_turbofanned, int stack_slots, int safepoint_table_offset,
+      int handler_table_offset);
+
+  MUST_USE_RESULT AllocationResult AllocateJSPromise(
+      JSFunction* constructor, PretenureFlag pretenure = NOT_TENURED);
 
   void set_force_oom(bool value) { force_oom_ = value; }
 
@@ -2400,6 +2434,8 @@ class Heap {
   // Observer that can cause early scavenge start.
   StressScavengeObserver* stress_scavenge_observer_;
 
+  bool allocation_step_in_progress_;
+
   // The maximum percent of the marking limit reached wihout causing marking.
   // This is tracked when specyfing --fuzzer-gc-analysis.
   double max_marking_limit_reached_;
@@ -2658,6 +2694,7 @@ class AlwaysAllocateScope {
   Heap* heap_;
 };
 
+// The CodeSpaceMemoryModificationScope can only be used by the main thread.
 class CodeSpaceMemoryModificationScope {
  public:
   explicit inline CodeSpaceMemoryModificationScope(Heap* heap);
@@ -2667,6 +2704,9 @@ class CodeSpaceMemoryModificationScope {
   Heap* heap_;
 };
 
+// The CodePageMemoryModificationScope does not check if tansitions to
+// writeable and back to executable are actually allowed, i.e. the MemoryChunk
+// was registered to be executable. It can be used by concurrent threads.
 class CodePageMemoryModificationScope {
  public:
   explicit inline CodePageMemoryModificationScope(MemoryChunk* chunk);
@@ -2689,7 +2729,8 @@ class CodePageMemoryModificationScope {
 class VerifyPointersVisitor : public ObjectVisitor, public RootVisitor {
  public:
   void VisitPointers(HeapObject* host, Object** start, Object** end) override;
-  void VisitRootPointers(Root root, Object** start, Object** end) override;
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override;
 
  private:
   void VerifyPointers(Object** start, Object** end);
@@ -2699,7 +2740,8 @@ class VerifyPointersVisitor : public ObjectVisitor, public RootVisitor {
 // Verify that all objects are Smis.
 class VerifySmisVisitor : public RootVisitor {
  public:
-  void VisitRootPointers(Root root, Object** start, Object** end) override;
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override;
 };
 
 // Space iterator for iterating over all the paged spaces of the heap: Map
diff --git a/deps/v8/src/heap/incremental-marking.cc b/deps/v8/src/heap/incremental-marking.cc
index 4868adc26e..a7b56e4315 100644
--- a/deps/v8/src/heap/incremental-marking.cc
+++ b/deps/v8/src/heap/incremental-marking.cc
@@ -203,11 +203,13 @@ class IncrementalMarkingRootMarkingVisitor : public RootVisitor {
       IncrementalMarking* incremental_marking)
       : heap_(incremental_marking->heap()) {}
 
-  void VisitRootPointer(Root root, Object** p) override {
+  void VisitRootPointer(Root root, const char* description,
+                        Object** p) override {
     MarkObjectByPointer(p);
   }
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
   }
 
@@ -653,15 +655,17 @@ bool IncrementalMarking::IsFixedArrayWithProgressBar(HeapObject* obj) {
 
 int IncrementalMarking::VisitObject(Map* map, HeapObject* obj) {
   DCHECK(marking_state()->IsGrey(obj) || marking_state()->IsBlack(obj));
-  // The object can already be black in two cases:
-  // 1. The object is a fixed array with the progress bar.
-  // 2. The object is a JSObject that was colored black before
-  //    unsafe layout change.
-  // 3. The object is a string that was colored black before
-  //    unsafe layout change.
   if (!marking_state()->GreyToBlack(obj)) {
-    DCHECK(IsFixedArrayWithProgressBar(obj) || obj->IsJSObject() ||
-           obj->IsString());
+    // The object can already be black in these cases:
+    // 1. The object is a fixed array with the progress bar.
+    // 2. The object is a JSObject that was colored black before
+    //    unsafe layout change.
+    // 3. The object is a string that was colored black before
+    //    unsafe layout change.
+    // 4. The object is materizalized by the deoptimizer.
+    DCHECK(obj->IsHashTable() || obj->IsPropertyArray() ||
+           obj->IsContextExtension() || obj->IsFixedArray() ||
+           obj->IsJSObject() || obj->IsString());
   }
   DCHECK(marking_state()->IsBlack(obj));
   WhiteToGreyAndPush(map);
diff --git a/deps/v8/src/heap/invalidated-slots-inl.h b/deps/v8/src/heap/invalidated-slots-inl.h
index b62aa93cde..8ca289cf1a 100644
--- a/deps/v8/src/heap/invalidated-slots-inl.h
+++ b/deps/v8/src/heap/invalidated-slots-inl.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_INVALIDATED_SLOTS_INL_H
-#define V8_INVALIDATED_SLOTS_INL_H
+#ifndef V8_HEAP_INVALIDATED_SLOTS_INL_H_
+#define V8_HEAP_INVALIDATED_SLOTS_INL_H_
 
 #include <map>
 
@@ -67,4 +67,4 @@ bool InvalidatedSlotsFilter::IsValid(Address slot) {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_INVALIDATED_SLOTS_INL_H
+#endif  // V8_HEAP_INVALIDATED_SLOTS_INL_H_
diff --git a/deps/v8/src/heap/invalidated-slots.h b/deps/v8/src/heap/invalidated-slots.h
index 78ac03bc79..e9410575a3 100644
--- a/deps/v8/src/heap/invalidated-slots.h
+++ b/deps/v8/src/heap/invalidated-slots.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_INVALIDATED_SLOTS_H
-#define V8_INVALIDATED_SLOTS_H
+#ifndef V8_HEAP_INVALIDATED_SLOTS_H_
+#define V8_HEAP_INVALIDATED_SLOTS_H_
 
 #include <map>
 #include <stack>
@@ -51,4 +51,4 @@ class InvalidatedSlotsFilter {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_INVALIDATED_SLOTS_H
+#endif  // V8_HEAP_INVALIDATED_SLOTS_H_
diff --git a/deps/v8/src/heap/item-parallel-job.cc b/deps/v8/src/heap/item-parallel-job.cc
new file mode 100644
index 0000000000..1c8d4c8ac4
--- /dev/null
+++ b/deps/v8/src/heap/item-parallel-job.cc
@@ -0,0 +1,130 @@
+// Copyright 2018 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/heap/item-parallel-job.h"
+
+#include "src/base/platform/semaphore.h"
+#include "src/v8.h"
+
+namespace v8 {
+namespace internal {
+
+ItemParallelJob::Task::Task(Isolate* isolate) : CancelableTask(isolate) {}
+
+ItemParallelJob::Task::~Task() {
+  // The histogram is reset in RunInternal(). If it's still around it means
+  // this task was cancelled before being scheduled.
+  if (gc_parallel_task_latency_histogram_)
+    gc_parallel_task_latency_histogram_->RecordAbandon();
+}
+
+void ItemParallelJob::Task::SetupInternal(
+    base::Semaphore* on_finish, std::vector<Item*>* items, size_t start_index,
+    base::Optional<AsyncTimedHistogram> gc_parallel_task_latency_histogram) {
+  on_finish_ = on_finish;
+  items_ = items;
+
+  if (start_index < items->size()) {
+    cur_index_ = start_index;
+  } else {
+    items_considered_ = items_->size();
+  }
+
+  gc_parallel_task_latency_histogram_ =
+      std::move(gc_parallel_task_latency_histogram);
+}
+
+void ItemParallelJob::Task::RunInternal() {
+  if (gc_parallel_task_latency_histogram_) {
+    gc_parallel_task_latency_histogram_->RecordDone();
+    gc_parallel_task_latency_histogram_.reset();
+  }
+
+  RunInParallel();
+  on_finish_->Signal();
+}
+
+ItemParallelJob::ItemParallelJob(CancelableTaskManager* cancelable_task_manager,
+                                 base::Semaphore* pending_tasks)
+    : cancelable_task_manager_(cancelable_task_manager),
+      pending_tasks_(pending_tasks) {}
+
+ItemParallelJob::~ItemParallelJob() {
+  for (size_t i = 0; i < items_.size(); i++) {
+    Item* item = items_[i];
+    CHECK(item->IsFinished());
+    delete item;
+  }
+}
+
+void ItemParallelJob::Run(std::shared_ptr<Counters> async_counters) {
+  DCHECK_GT(tasks_.size(), 0);
+  const size_t num_items = items_.size();
+  const size_t num_tasks = tasks_.size();
+
+  TRACE_EVENT_INSTANT2(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                       "ItemParallelJob::Run", TRACE_EVENT_SCOPE_THREAD,
+                       "num_tasks", static_cast<int>(num_tasks), "num_items",
+                       static_cast<int>(num_items));
+
+  AsyncTimedHistogram gc_parallel_task_latency_histogram(
+      async_counters->gc_parallel_task_latency(), async_counters);
+
+  // Some jobs have more tasks than items (when the items are mere coarse
+  // grain tasks that generate work dynamically for a second phase which all
+  // tasks participate in). Some jobs even have 0 items to preprocess but
+  // still have multiple tasks.
+  // TODO(gab): Figure out a cleaner scheme for this.
+  const size_t num_tasks_processing_items = Min(num_items, tasks_.size());
+
+  // In the event of an uneven workload, distribute an extra item to the first
+  // |items_remainder| tasks.
+  const size_t items_remainder = num_tasks_processing_items > 0
+                                     ? num_items % num_tasks_processing_items
+                                     : 0;
+  // Base |items_per_task|, will be bumped by 1 for the first
+  // |items_remainder| tasks.
+  const size_t items_per_task = num_tasks_processing_items > 0
+                                    ? num_items / num_tasks_processing_items
+                                    : 0;
+  CancelableTaskManager::Id* task_ids =
+      new CancelableTaskManager::Id[num_tasks];
+  Task* main_task = nullptr;
+  for (size_t i = 0, start_index = 0; i < num_tasks;
+       i++, start_index += items_per_task + (i < items_remainder ? 1 : 0)) {
+    Task* task = tasks_[i];
+
+    // By definition there are less |items_remainder| to distribute then
+    // there are tasks processing items so this cannot overflow while we are
+    // assigning work items.
+    DCHECK_IMPLIES(start_index >= num_items, i >= num_tasks_processing_items);
+
+    task->SetupInternal(pending_tasks_, &items_, start_index,
+                        i > 0 ? gc_parallel_task_latency_histogram
+                              : base::Optional<AsyncTimedHistogram>());
+    task_ids[i] = task->id();
+    if (i > 0) {
+      V8::GetCurrentPlatform()->CallOnBackgroundThread(
+          task, v8::Platform::kShortRunningTask);
+    } else {
+      main_task = task;
+    }
+  }
+
+  // Contribute on main thread.
+  main_task->Run();
+  delete main_task;
+
+  // Wait for background tasks.
+  for (size_t i = 0; i < num_tasks; i++) {
+    if (cancelable_task_manager_->TryAbort(task_ids[i]) !=
+        CancelableTaskManager::kTaskAborted) {
+      pending_tasks_->Wait();
+    }
+  }
+  delete[] task_ids;
+}
+
+}  // namespace internal
+}  // namespace v8
diff --git a/deps/v8/src/heap/item-parallel-job.h b/deps/v8/src/heap/item-parallel-job.h
index 23c709f87b..4c21f69ca9 100644
--- a/deps/v8/src/heap/item-parallel-job.h
+++ b/deps/v8/src/heap/item-parallel-job.h
@@ -2,18 +2,29 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_HEAP_ITEM_PARALLEL_JOB_
-#define V8_HEAP_ITEM_PARALLEL_JOB_
+#ifndef V8_HEAP_ITEM_PARALLEL_JOB_H_
+#define V8_HEAP_ITEM_PARALLEL_JOB_H_
 
+#include <memory>
 #include <vector>
 
-#include "src/base/platform/semaphore.h"
+#include "src/base/atomic-utils.h"
+#include "src/base/logging.h"
+#include "src/base/macros.h"
+#include "src/base/optional.h"
 #include "src/cancelable-task.h"
-#include "src/v8.h"
+#include "src/counters.h"
+#include "src/globals.h"
 
 namespace v8 {
+
+namespace base {
+class Semaphore;
+}
+
 namespace internal {
 
+class Counters;
 class Isolate;
 
 // This class manages background tasks that process a set of items in parallel.
@@ -25,14 +36,17 @@ class Isolate;
 //
 // Items need to be marked as finished after processing them. Task and Item
 // ownership is transferred to the job.
-class ItemParallelJob {
+//
+// Each parallel (non-main thread) task will report the time between the job
+// being created and it being scheduled to |gc_parallel_task_latency_histogram|.
+class V8_EXPORT_PRIVATE ItemParallelJob {
  public:
   class Task;
 
-  class Item {
+  class V8_EXPORT_PRIVATE Item {
    public:
-    Item() : state_(kAvailable) {}
-    virtual ~Item() {}
+    Item() = default;
+    virtual ~Item() = default;
 
     // Marks an item as being finished.
     void MarkFinished() { CHECK(state_.TrySetValue(kProcessing, kFinished)); }
@@ -45,7 +59,7 @@ class ItemParallelJob {
     }
     bool IsFinished() { return state_.Value() == kFinished; }
 
-    base::AtomicValue<ProcessingState> state_;
+    base::AtomicValue<ProcessingState> state_{kAvailable};
 
     friend class ItemParallelJob;
     friend class ItemParallelJob::Task;
@@ -53,15 +67,10 @@ class ItemParallelJob {
     DISALLOW_COPY_AND_ASSIGN(Item);
   };
 
-  class Task : public CancelableTask {
+  class V8_EXPORT_PRIVATE Task : public CancelableTask {
    public:
-    explicit Task(Isolate* isolate)
-        : CancelableTask(isolate),
-          items_(nullptr),
-          cur_index_(0),
-          items_considered_(0),
-          on_finish_(nullptr) {}
-    virtual ~Task() {}
+    explicit Task(Isolate* isolate);
+    virtual ~Task();
 
     virtual void RunInParallel() = 0;
 
@@ -85,42 +94,36 @@ class ItemParallelJob {
     }
 
    private:
-    void SetupInternal(base::Semaphore* on_finish, std::vector<Item*>* items,
-                       size_t start_index) {
-      on_finish_ = on_finish;
-      items_ = items;
-      cur_index_ = start_index;
-    }
+    friend class ItemParallelJob;
+    friend class Item;
 
-    // We don't allow overriding this method any further.
-    void RunInternal() final {
-      RunInParallel();
-      on_finish_->Signal();
-    }
+    // Sets up state required before invoking Run(). If
+    // |start_index is >= items_.size()|, this task will not process work items
+    // (some jobs have more tasks than work items in order to parallelize post-
+    // processing, e.g. scavenging). If |gc_parallel_task_latency_histogram| is
+    // provided, it will be used to report histograms on the latency between
+    // posting the task and it being scheduled.
+    void SetupInternal(
+        base::Semaphore* on_finish, std::vector<Item*>* items,
+        size_t start_index,
+        base::Optional<AsyncTimedHistogram> gc_parallel_task_latency_histogram);
 
-    std::vector<Item*>* items_;
-    size_t cur_index_;
-    size_t items_considered_;
-    base::Semaphore* on_finish_;
+    // We don't allow overriding this method any further.
+    void RunInternal() final;
 
-    friend class ItemParallelJob;
-    friend class Item;
+    std::vector<Item*>* items_ = nullptr;
+    size_t cur_index_ = 0;
+    size_t items_considered_ = 0;
+    base::Semaphore* on_finish_ = nullptr;
+    base::Optional<AsyncTimedHistogram> gc_parallel_task_latency_histogram_;
 
     DISALLOW_COPY_AND_ASSIGN(Task);
   };
 
   ItemParallelJob(CancelableTaskManager* cancelable_task_manager,
-                  base::Semaphore* pending_tasks)
-      : cancelable_task_manager_(cancelable_task_manager),
-        pending_tasks_(pending_tasks) {}
-
-  ~ItemParallelJob() {
-    for (size_t i = 0; i < items_.size(); i++) {
-      Item* item = items_[i];
-      CHECK(item->IsFinished());
-      delete item;
-    }
-  }
+                  base::Semaphore* pending_tasks);
+
+  ~ItemParallelJob();
 
   // Adds a task to the job. Transfers ownership to the job.
   void AddTask(Task* task) { tasks_.push_back(task); }
@@ -131,42 +134,9 @@ class ItemParallelJob {
   int NumberOfItems() const { return static_cast<int>(items_.size()); }
   int NumberOfTasks() const { return static_cast<int>(tasks_.size()); }
 
-  void Run() {
-    DCHECK_GE(tasks_.size(), 0);
-    const size_t num_tasks = tasks_.size();
-    const size_t num_items = items_.size();
-    const size_t items_per_task = (num_items + num_tasks - 1) / num_tasks;
-    CancelableTaskManager::Id* task_ids =
-        new CancelableTaskManager::Id[num_tasks];
-    size_t start_index = 0;
-    Task* main_task = nullptr;
-    Task* task = nullptr;
-    for (size_t i = 0; i < num_tasks; i++, start_index += items_per_task) {
-      task = tasks_[i];
-      if (start_index >= num_items) {
-        start_index -= num_items;
-      }
-      task->SetupInternal(pending_tasks_, &items_, start_index);
-      task_ids[i] = task->id();
-      if (i > 0) {
-        V8::GetCurrentPlatform()->CallOnBackgroundThread(
-            task, v8::Platform::kShortRunningTask);
-      } else {
-        main_task = task;
-      }
-    }
-    // Contribute on main thread.
-    main_task->Run();
-    delete main_task;
-    // Wait for background tasks.
-    for (size_t i = 0; i < num_tasks; i++) {
-      if (cancelable_task_manager_->TryAbort(task_ids[i]) !=
-          CancelableTaskManager::kTaskAborted) {
-        pending_tasks_->Wait();
-      }
-    }
-    delete[] task_ids;
-  }
+  // Runs this job. Reporting metrics in a thread-safe manner to
+  // |async_counters|.
+  void Run(std::shared_ptr<Counters> async_counters);
 
  private:
   std::vector<Item*> items_;
@@ -179,4 +149,4 @@ class ItemParallelJob {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_HEAP_ITEM_PARALLEL_JOB_
+#endif  // V8_HEAP_ITEM_PARALLEL_JOB_H_
diff --git a/deps/v8/src/heap/mark-compact.cc b/deps/v8/src/heap/mark-compact.cc
index 30a7e55d6b..c6c8c29962 100644
--- a/deps/v8/src/heap/mark-compact.cc
+++ b/deps/v8/src/heap/mark-compact.cc
@@ -16,7 +16,6 @@
 #include "src/global-handles.h"
 #include "src/heap/array-buffer-collector.h"
 #include "src/heap/array-buffer-tracker-inl.h"
-#include "src/heap/concurrent-marking.h"
 #include "src/heap/gc-tracer.h"
 #include "src/heap/incremental-marking.h"
 #include "src/heap/invalidated-slots-inl.h"
@@ -72,7 +71,8 @@ class MarkingVerifier : public ObjectVisitor, public RootVisitor {
     VerifyPointers(start, end);
   }
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     VerifyPointers(start, end);
   }
 
@@ -240,7 +240,8 @@ class EvacuationVerifier : public ObjectVisitor, public RootVisitor {
     VerifyPointers(start, end);
   }
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     VerifyPointers(start, end);
   }
 
@@ -369,12 +370,14 @@ class RootMarkingVisitorSeedOnly : public RootVisitor {
     buffered_objects_.reserve(kBufferSize);
   }
 
-  void VisitRootPointer(Root root, Object** p) override {
+  void VisitRootPointer(Root root, const char* description,
+                        Object** p) override {
     if (!(*p)->IsHeapObject()) return;
     AddObject(*p);
   }
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     for (Object** p = start; p < end; p++) {
       if (!(*p)->IsHeapObject()) continue;
       AddObject(*p);
@@ -404,14 +407,22 @@ class RootMarkingVisitorSeedOnly : public RootVisitor {
   std::vector<Object*> buffered_objects_;
 };
 
-}  // namespace
-
-static int NumberOfAvailableCores() {
-  return Max(
-      1, static_cast<int>(
-             V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads()));
+int NumberOfAvailableCores() {
+  static int num_cores =
+      static_cast<int>(
+          V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads()) +
+      1;
+  // This number of cores should be greater than zero and never change.
+  DCHECK_GE(num_cores, 1);
+  DCHECK_EQ(
+      num_cores,
+      1 + static_cast<int>(
+              V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads()));
+  return num_cores;
 }
 
+}  // namespace
+
 int MarkCompactCollectorBase::NumberOfParallelCompactionTasks(int pages) {
   DCHECK_GT(pages, 0);
   return FLAG_parallel_compaction ? Min(NumberOfAvailableCores(), pages) : 1;
@@ -855,7 +866,7 @@ void MarkCompactCollector::Prepare() {
   if (was_marked_incrementally_ && heap_->ShouldAbortIncrementalMarking()) {
     heap()->incremental_marking()->Stop();
     heap()->incremental_marking()->AbortBlackAllocation();
-    FinishConcurrentMarking();
+    FinishConcurrentMarking(ConcurrentMarking::StopRequest::PREEMPT_TASKS);
     heap()->incremental_marking()->Deactivate();
     ClearMarkbits();
     AbortWeakCollections();
@@ -891,9 +902,10 @@ void MarkCompactCollector::Prepare() {
 #endif
 }
 
-void MarkCompactCollector::FinishConcurrentMarking() {
+void MarkCompactCollector::FinishConcurrentMarking(
+    ConcurrentMarking::StopRequest stop_request) {
   if (FLAG_concurrent_marking) {
-    heap()->concurrent_marking()->EnsureCompleted();
+    heap()->concurrent_marking()->Stop(stop_request);
     heap()->concurrent_marking()->FlushLiveBytes(non_atomic_marking_state());
   }
 }
@@ -965,11 +977,12 @@ class MarkCompactCollector::RootMarkingVisitor final : public RootVisitor {
   explicit RootMarkingVisitor(MarkCompactCollector* collector)
       : collector_(collector) {}
 
-  void VisitRootPointer(Root root, Object** p) final {
+  void VisitRootPointer(Root root, const char* description, Object** p) final {
     MarkObjectByPointer(root, p);
   }
 
-  void VisitRootPointers(Root root, Object** start, Object** end) final {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) final {
     for (Object** p = start; p < end; p++) MarkObjectByPointer(root, p);
   }
 
@@ -1058,7 +1071,8 @@ class ExternalStringTableCleaner : public RootVisitor {
  public:
   explicit ExternalStringTableCleaner(Heap* heap) : heap_(heap) {}
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     // Visit all HeapObject pointers in [start, end).
     MarkCompactCollector::NonAtomicMarkingState* marking_state =
         heap_->mark_compact_collector()->non_atomic_marking_state();
@@ -1093,7 +1107,8 @@ class YoungGenerationExternalStringTableCleaner : public RootVisitor {
       : heap_(collector->heap()),
         marking_state_(collector->non_atomic_marking_state()) {}
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     DCHECK_EQ(static_cast<int>(root),
               static_cast<int>(Root::kExternalStringsTable));
     // Visit all HeapObject pointers in [start, end).
@@ -1391,7 +1406,8 @@ class EvacuateVisitorBase : public HeapObjectVisitor {
 #ifdef VERIFY_HEAP
     if (AbortCompactionForTesting(object)) return false;
 #endif  // VERIFY_HEAP
-    AllocationAlignment alignment = object->RequiredAlignment();
+    AllocationAlignment alignment =
+        HeapObject::RequiredAlignment(object->map());
     AllocationResult allocation =
         local_allocator_->Allocate(target_space, size, alignment);
     if (allocation.To(target_object)) {
@@ -1496,7 +1512,8 @@ class EvacuateNewSpaceVisitor final : public EvacuateVisitorBase {
 
   inline AllocationSpace AllocateTargetObject(HeapObject* old_object, int size,
                                               HeapObject** target_object) {
-    AllocationAlignment alignment = old_object->RequiredAlignment();
+    AllocationAlignment alignment =
+        HeapObject::RequiredAlignment(old_object->map());
     AllocationSpace space_allocated_in = NEW_SPACE;
     AllocationResult allocation =
         local_allocator_->Allocate(NEW_SPACE, size, alignment);
@@ -1758,11 +1775,13 @@ class MinorMarkCompactCollector::RootMarkingVisitor : public RootVisitor {
       : collector_(collector),
         marking_state_(collector_->non_atomic_marking_state()) {}
 
-  void VisitRootPointer(Root root, Object** p) override {
+  void VisitRootPointer(Root root, const char* description,
+                        Object** p) override {
     MarkObjectByPointer(p);
   }
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
   }
 
@@ -1883,6 +1902,8 @@ class BatchedRootMarkingItem : public MarkingItem {
   virtual ~BatchedRootMarkingItem() {}
 
   void Process(YoungGenerationMarkingTask* task) override {
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                 "BatchedRootMarkingItem::Process");
     for (Object* object : objects_) {
       task->MarkObject(object);
     }
@@ -1900,6 +1921,8 @@ class PageMarkingItem : public MarkingItem {
   virtual ~PageMarkingItem() { global_slots_->Increment(slots_); }
 
   void Process(YoungGenerationMarkingTask* task) override {
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                 "PageMarkingItem::Process");
     base::LockGuard<base::Mutex> guard(chunk_->mutex());
     MarkUntypedPointers(task);
     MarkTypedPointers(task);
@@ -1956,6 +1979,8 @@ class GlobalHandlesMarkingItem : public MarkingItem {
   virtual ~GlobalHandlesMarkingItem() {}
 
   void Process(YoungGenerationMarkingTask* task) override {
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                 "GlobalHandlesMarkingItem::Process");
     GlobalHandlesRootMarkingVisitor visitor(task);
     global_handles_
         ->IterateNewSpaceStrongAndDependentRootsAndIdentifyUnmodified(
@@ -1968,12 +1993,14 @@ class GlobalHandlesMarkingItem : public MarkingItem {
     explicit GlobalHandlesRootMarkingVisitor(YoungGenerationMarkingTask* task)
         : task_(task) {}
 
-    void VisitRootPointer(Root root, Object** p) override {
+    void VisitRootPointer(Root root, const char* description,
+                          Object** p) override {
       DCHECK_EQ(Root::kGlobalHandles, root);
       task_->MarkObject(*p);
     }
 
-    void VisitRootPointers(Root root, Object** start, Object** end) override {
+    void VisitRootPointers(Root root, const char* description, Object** start,
+                           Object** end) override {
       DCHECK_EQ(Root::kGlobalHandles, root);
       for (Object** p = start; p < end; p++) {
         task_->MarkObject(*p);
@@ -2061,7 +2088,7 @@ void MinorMarkCompactCollector::MarkRootSetInParallel() {
         job.AddTask(
             new YoungGenerationMarkingTask(isolate(), this, worklist(), i));
       }
-      job.Run();
+      job.Run(isolate()->async_counters());
       DCHECK(worklist()->IsGlobalEmpty());
     }
   }
@@ -2336,7 +2363,8 @@ void MarkCompactCollector::MarkLiveObjects() {
     }
     ProcessMarkingWorklist();
 
-    FinishConcurrentMarking();
+    FinishConcurrentMarking(
+        ConcurrentMarking::StopRequest::COMPLETE_ONGOING_TASKS);
     ProcessMarkingWorklist();
   }
 
@@ -2849,11 +2877,13 @@ class PointersUpdatingVisitor : public ObjectVisitor, public RootVisitor {
     for (Object** p = start; p < end; p++) UpdateSlotInternal(p);
   }
 
-  void VisitRootPointer(Root root, Object** p) override {
+  void VisitRootPointer(Root root, const char* description,
+                        Object** p) override {
     UpdateSlotInternal(p);
   }
 
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) override {
     for (Object** p = start; p < end; p++) UpdateSlotInternal(p);
   }
 
@@ -3009,6 +3039,7 @@ class Evacuator : public Malloced {
 };
 
 void Evacuator::EvacuatePage(Page* page) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"), "Evacuator::EvacuatePage");
   DCHECK(page->SweepingDone());
   intptr_t saved_live_bytes = 0;
   double evacuation_time = 0.0;
@@ -3066,11 +3097,15 @@ class FullEvacuator : public Evacuator {
 };
 
 void FullEvacuator::RawEvacuatePage(Page* page, intptr_t* live_bytes) {
+  const EvacuationMode evacuation_mode = ComputeEvacuationMode(page);
+  TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+               "FullEvacuator::RawEvacuatePage", "evacuation_mode",
+               evacuation_mode);
   MarkCompactCollector::NonAtomicMarkingState* marking_state =
       collector_->non_atomic_marking_state();
   *live_bytes = marking_state->live_bytes(page);
   HeapObject* failed_object = nullptr;
-  switch (ComputeEvacuationMode(page)) {
+  switch (evacuation_mode) {
     case kObjectsNewToOld:
       LiveObjectVisitor::VisitBlackObjectsNoFail(
           page, marking_state, &new_space_visitor_,
@@ -3127,6 +3162,8 @@ class YoungGenerationEvacuator : public Evacuator {
 
 void YoungGenerationEvacuator::RawEvacuatePage(Page* page,
                                                intptr_t* live_bytes) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+               "YoungGenerationEvacuator::RawEvacuatePage");
   MinorMarkCompactCollector::NonAtomicMarkingState* marking_state =
       collector_->non_atomic_marking_state();
   *live_bytes = marking_state->live_bytes(page);
@@ -3241,7 +3278,7 @@ void MarkCompactCollectorBase::CreateAndExecuteEvacuationTasks(
       evacuators[i]->AddObserver(migration_observer);
     job->AddTask(new PageEvacuationTask(heap()->isolate(), evacuators[i]));
   }
-  job->Run();
+  job->Run(isolate()->async_counters());
   for (int i = 0; i < wanted_num_tasks; i++) {
     evacuators[i]->Finalize();
     delete evacuators[i];
@@ -3249,15 +3286,16 @@ void MarkCompactCollectorBase::CreateAndExecuteEvacuationTasks(
   delete[] evacuators;
 
   if (FLAG_trace_evacuation) {
-    PrintIsolate(isolate(),
-                 "%8.0f ms: evacuation-summary: parallel=%s pages=%d "
-                 "wanted_tasks=%d tasks=%d cores=%" PRIuS
-                 " live_bytes=%" V8PRIdPTR " compaction_speed=%.f\n",
-                 isolate()->time_millis_since_init(),
-                 FLAG_parallel_compaction ? "yes" : "no", job->NumberOfItems(),
-                 wanted_num_tasks, job->NumberOfTasks(),
-                 V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads(),
-                 live_bytes, compaction_speed);
+    PrintIsolate(
+        isolate(),
+        "%8.0f ms: evacuation-summary: parallel=%s pages=%d "
+        "wanted_tasks=%d tasks=%d cores=%" PRIuS " live_bytes=%" V8PRIdPTR
+        " compaction_speed=%.f\n",
+        isolate()->time_millis_since_init(),
+        FLAG_parallel_compaction ? "yes" : "no", job->NumberOfItems(),
+        wanted_num_tasks, job->NumberOfTasks(),
+        V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads() + 1,
+        live_bytes, compaction_speed);
   }
 }
 
@@ -3365,6 +3403,8 @@ bool LiveObjectVisitor::VisitBlackObjects(MemoryChunk* chunk,
                                           Visitor* visitor,
                                           IterationMode iteration_mode,
                                           HeapObject** failed_object) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+               "LiveObjectVisitor::VisitBlackObjects");
   for (auto object_and_size :
        LiveObjectRange<kBlackObjects>(chunk, marking_state->bitmap(chunk))) {
     HeapObject* const object = object_and_size.first;
@@ -3389,6 +3429,8 @@ void LiveObjectVisitor::VisitBlackObjectsNoFail(MemoryChunk* chunk,
                                                 MarkingState* marking_state,
                                                 Visitor* visitor,
                                                 IterationMode iteration_mode) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+               "LiveObjectVisitor::VisitBlackObjectsNoFail");
   for (auto object_and_size :
        LiveObjectRange<kBlackObjects>(chunk, marking_state->bitmap(chunk))) {
     HeapObject* const object = object_and_size.first;
@@ -3407,6 +3449,8 @@ void LiveObjectVisitor::VisitGreyObjectsNoFail(MemoryChunk* chunk,
                                                MarkingState* marking_state,
                                                Visitor* visitor,
                                                IterationMode iteration_mode) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+               "LiveObjectVisitor::VisitGreyObjectsNoFail");
   for (auto object_and_size :
        LiveObjectRange<kGreyObjects>(chunk, marking_state->bitmap(chunk))) {
     HeapObject* const object = object_and_size.first;
@@ -3553,6 +3597,8 @@ class ToSpaceUpdatingItem : public UpdatingItem {
 
  private:
   void ProcessVisitAll() {
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                 "ToSpaceUpdatingItem::ProcessVisitAll");
     PointersUpdatingVisitor visitor;
     for (Address cur = start_; cur < end_;) {
       HeapObject* object = HeapObject::FromAddress(cur);
@@ -3564,6 +3610,8 @@ class ToSpaceUpdatingItem : public UpdatingItem {
   }
 
   void ProcessVisitLive() {
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                 "ToSpaceUpdatingItem::ProcessVisitLive");
     // For young generation evacuations we want to visit grey objects, for
     // full MC, we need to visit black objects.
     PointersUpdatingVisitor visitor;
@@ -3592,13 +3640,14 @@ class RememberedSetUpdatingItem : public UpdatingItem {
   virtual ~RememberedSetUpdatingItem() {}
 
   void Process() override {
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                 "RememberedSetUpdatingItem::Process");
     base::LockGuard<base::Mutex> guard(chunk_->mutex());
     UpdateUntypedPointers();
     UpdateTypedPointers();
   }
 
  private:
-  template <AccessMode access_mode>
   inline SlotCallbackResult CheckAndUpdateOldToNewSlot(Address slot_address) {
     Object** slot = reinterpret_cast<Object**>(slot_address);
     if (heap_->InFromSpace(*slot)) {
@@ -3606,13 +3655,7 @@ class RememberedSetUpdatingItem : public UpdatingItem {
       DCHECK(heap_object->IsHeapObject());
       MapWord map_word = heap_object->map_word();
       if (map_word.IsForwardingAddress()) {
-        if (access_mode == AccessMode::ATOMIC) {
-          HeapObject** heap_obj_slot = reinterpret_cast<HeapObject**>(slot);
-          base::AsAtomicPointer::Relaxed_Store(heap_obj_slot,
-                                               map_word.ToForwardingAddress());
-        } else {
-          *slot = map_word.ToForwardingAddress();
-        }
+        *slot = map_word.ToForwardingAddress();
       }
       // If the object was in from space before and is after executing the
       // callback in to space, the object is still live.
@@ -3648,12 +3691,10 @@ class RememberedSetUpdatingItem : public UpdatingItem {
 
   void UpdateUntypedPointers() {
     if (chunk_->slot_set<OLD_TO_NEW, AccessMode::NON_ATOMIC>() != nullptr) {
-        RememberedSet<OLD_TO_NEW>::Iterate(
-            chunk_,
-            [this](Address slot) {
-              return CheckAndUpdateOldToNewSlot<AccessMode::NON_ATOMIC>(slot);
-            },
-            SlotSet::PREFREE_EMPTY_BUCKETS);
+      RememberedSet<OLD_TO_NEW>::Iterate(
+          chunk_,
+          [this](Address slot) { return CheckAndUpdateOldToNewSlot(slot); },
+          SlotSet::PREFREE_EMPTY_BUCKETS);
     }
     if ((updating_mode_ == RememberedSetUpdatingMode::ALL) &&
         (chunk_->slot_set<OLD_TO_OLD, AccessMode::NON_ATOMIC>() != nullptr)) {
@@ -3692,7 +3733,7 @@ class RememberedSetUpdatingItem : public UpdatingItem {
           [isolate, this](SlotType slot_type, Address host_addr, Address slot) {
             return UpdateTypedSlotHelper::UpdateTypedSlot(
                 isolate, slot_type, slot, [this](Object** slot) {
-                  return CheckAndUpdateOldToNewSlot<AccessMode::NON_ATOMIC>(
+                  return CheckAndUpdateOldToNewSlot(
                       reinterpret_cast<Address>(slot));
                 });
           });
@@ -3748,6 +3789,8 @@ class GlobalHandlesUpdatingItem : public UpdatingItem {
   virtual ~GlobalHandlesUpdatingItem() {}
 
   void Process() override {
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                 "GlobalHandlesUpdatingItem::Process");
     PointersUpdatingVisitor updating_visitor;
     global_handles_->IterateNewSpaceRoots(&updating_visitor, start_, end_);
   }
@@ -3772,6 +3815,9 @@ class ArrayBufferTrackerUpdatingItem : public UpdatingItem {
   virtual ~ArrayBufferTrackerUpdatingItem() {}
 
   void Process() override {
+    TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
+                 "ArrayBufferTrackerUpdatingItem::Process", "EvacuationState",
+                 state_);
     switch (state_) {
       case EvacuationState::kRegular:
         ArrayBufferTracker::ProcessBuffers(
@@ -3922,7 +3968,7 @@ void MarkCompactCollector::UpdatePointersAfterEvacuation() {
           isolate(),
           GCTracer::BackgroundScope::MC_BACKGROUND_EVACUATE_UPDATE_POINTERS));
     }
-    updating_job.Run();
+    updating_job.Run(isolate()->async_counters());
   }
 
   {
@@ -3954,7 +4000,7 @@ void MarkCompactCollector::UpdatePointersAfterEvacuation() {
             isolate(),
             GCTracer::BackgroundScope::MC_BACKGROUND_EVACUATE_UPDATE_POINTERS));
       }
-      updating_job.Run();
+      updating_job.Run(isolate()->async_counters());
       heap()->array_buffer_collector()->FreeAllocationsOnBackgroundThread();
     }
   }
@@ -4016,7 +4062,7 @@ void MinorMarkCompactCollector::UpdatePointersAfterEvacuation() {
   {
     TRACE_GC(heap()->tracer(),
              GCTracer::Scope::MINOR_MC_EVACUATE_UPDATE_POINTERS_SLOTS);
-    updating_job.Run();
+    updating_job.Run(isolate()->async_counters());
     heap()->array_buffer_collector()->FreeAllocationsOnBackgroundThread();
   }
 
diff --git a/deps/v8/src/heap/mark-compact.h b/deps/v8/src/heap/mark-compact.h
index 6fda00633c..755f0eb4eb 100644
--- a/deps/v8/src/heap/mark-compact.h
+++ b/deps/v8/src/heap/mark-compact.h
@@ -8,6 +8,7 @@
 #include <deque>
 #include <vector>
 
+#include "src/heap/concurrent-marking.h"
 #include "src/heap/marking.h"
 #include "src/heap/objects-visiting.h"
 #include "src/heap/spaces.h"
@@ -649,7 +650,9 @@ class MarkCompactCollector final : public MarkCompactCollectorBase {
   // choosing spaces to compact.
   void Prepare();
 
-  void FinishConcurrentMarking();
+  // Stop concurrent marking (either by preempting it right away or waiting for
+  // it to complete as requested by |stop_request|).
+  void FinishConcurrentMarking(ConcurrentMarking::StopRequest stop_request);
 
   bool StartCompaction();
 
diff --git a/deps/v8/src/heap/marking.h b/deps/v8/src/heap/marking.h
index 9b1fe61236..58630c52f0 100644
--- a/deps/v8/src/heap/marking.h
+++ b/deps/v8/src/heap/marking.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_MARKING_H
-#define V8_MARKING_H
+#ifndef V8_HEAP_MARKING_H_
+#define V8_HEAP_MARKING_H_
 
 #include "src/base/atomic-utils.h"
 #include "src/utils.h"
@@ -316,4 +316,4 @@ class Marking : public AllStatic {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_MARKING_H_
+#endif  // V8_HEAP_MARKING_H_
diff --git a/deps/v8/src/heap/memory-reducer.cc b/deps/v8/src/heap/memory-reducer.cc
index cc1030846a..77317a7b8a 100644
--- a/deps/v8/src/heap/memory-reducer.cc
+++ b/deps/v8/src/heap/memory-reducer.cc
@@ -201,6 +201,7 @@ MemoryReducer::State MemoryReducer::Step(const State& state,
 
 
 void MemoryReducer::ScheduleTimer(double time_ms, double delay_ms) {
+  if (!heap()->use_tasks()) return;
   DCHECK_LT(0, delay_ms);
   // Leave some room for precision error in task scheduler.
   const double kSlackMs = 100;
diff --git a/deps/v8/src/heap/memory-reducer.h b/deps/v8/src/heap/memory-reducer.h
index 0f0ad6eaa0..ce6564596e 100644
--- a/deps/v8/src/heap/memory-reducer.h
+++ b/deps/v8/src/heap/memory-reducer.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_HEAP_memory_reducer_H
-#define V8_HEAP_memory_reducer_H
+#ifndef V8_HEAP_MEMORY_REDUCER_H_
+#define V8_HEAP_MEMORY_REDUCER_H_
 
 #include "include/v8-platform.h"
 #include "src/base/macros.h"
@@ -171,4 +171,4 @@ class V8_EXPORT_PRIVATE MemoryReducer {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_HEAP_memory_reducer_H
+#endif  // V8_HEAP_MEMORY_REDUCER_H_
diff --git a/deps/v8/src/heap/object-stats.cc b/deps/v8/src/heap/object-stats.cc
index f58a472671..b854dabb2c 100644
--- a/deps/v8/src/heap/object-stats.cc
+++ b/deps/v8/src/heap/object-stats.cc
@@ -1,4 +1,5 @@
 // Copyright 2015 the V8 project authors. All rights reserved.
+//
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -12,6 +13,7 @@
 #include "src/counters.h"
 #include "src/globals.h"
 #include "src/heap/heap-inl.h"
+#include "src/heap/mark-compact.h"
 #include "src/isolate.h"
 #include "src/objects/compilation-cache-inl.h"
 #include "src/utils.h"
@@ -31,7 +33,6 @@ void ObjectStats::ClearObjectStats(bool clear_last_time_stats) {
     memset(object_counts_last_time_, 0, sizeof(object_counts_last_time_));
     memset(object_sizes_last_time_, 0, sizeof(object_sizes_last_time_));
   }
-  visited_fixed_array_sub_types_.clear();
 }
 
 // Tell the compiler to never inline this: occasionally, the optimizer will
@@ -99,23 +100,14 @@ void ObjectStats::PrintJSON(const char* key) {
 
 #define INSTANCE_TYPE_WRAPPER(name) \
   PrintInstanceTypeJSON(key, gc_count, #name, name);
-#define CODE_KIND_WRAPPER(name)                        \
-  PrintInstanceTypeJSON(key, gc_count, "*CODE_" #name, \
-                        FIRST_CODE_KIND_SUB_TYPE + Code::name);
-#define FIXED_ARRAY_SUB_INSTANCE_TYPE_WRAPPER(name)           \
-  PrintInstanceTypeJSON(key, gc_count, "*FIXED_ARRAY_" #name, \
-                        FIRST_FIXED_ARRAY_SUB_TYPE + name);
+
 #define VIRTUAL_INSTANCE_TYPE_WRAPPER(name) \
   PrintInstanceTypeJSON(key, gc_count, #name, FIRST_VIRTUAL_TYPE + name);
 
   INSTANCE_TYPE_LIST(INSTANCE_TYPE_WRAPPER)
-  CODE_KIND_LIST(CODE_KIND_WRAPPER)
-  FIXED_ARRAY_SUB_INSTANCE_TYPE_LIST(FIXED_ARRAY_SUB_INSTANCE_TYPE_WRAPPER)
   VIRTUAL_INSTANCE_TYPE_LIST(VIRTUAL_INSTANCE_TYPE_WRAPPER)
 
 #undef INSTANCE_TYPE_WRAPPER
-#undef CODE_KIND_WRAPPER
-#undef FIXED_ARRAY_SUB_INSTANCE_TYPE_WRAPPER
 #undef VIRTUAL_INSTANCE_TYPE_WRAPPER
 }
 
@@ -150,25 +142,15 @@ void ObjectStats::Dump(std::stringstream& stream) {
   stream << "\"type_data\":{";
 
 #define INSTANCE_TYPE_WRAPPER(name) DumpInstanceTypeData(stream, #name, name);
-#define CODE_KIND_WRAPPER(name)                \
-  DumpInstanceTypeData(stream, "*CODE_" #name, \
-                       FIRST_CODE_KIND_SUB_TYPE + Code::name);
 
-#define FIXED_ARRAY_SUB_INSTANCE_TYPE_WRAPPER(name)   \
-  DumpInstanceTypeData(stream, "*FIXED_ARRAY_" #name, \
-                       FIRST_FIXED_ARRAY_SUB_TYPE + name);
 #define VIRTUAL_INSTANCE_TYPE_WRAPPER(name) \
   DumpInstanceTypeData(stream, #name, FIRST_VIRTUAL_TYPE + name);
 
   INSTANCE_TYPE_LIST(INSTANCE_TYPE_WRAPPER);
-  CODE_KIND_LIST(CODE_KIND_WRAPPER);
-  FIXED_ARRAY_SUB_INSTANCE_TYPE_LIST(FIXED_ARRAY_SUB_INSTANCE_TYPE_WRAPPER);
   VIRTUAL_INSTANCE_TYPE_LIST(VIRTUAL_INSTANCE_TYPE_WRAPPER)
   stream << "\"END\":{}}}";
 
 #undef INSTANCE_TYPE_WRAPPER
-#undef CODE_KIND_WRAPPER
-#undef FIXED_ARRAY_SUB_INSTANCE_TYPE_WRAPPER
 #undef VIRTUAL_INSTANCE_TYPE_WRAPPER
 }
 
@@ -202,93 +184,88 @@ void ObjectStats::RecordObjectStats(InstanceType type, size_t size) {
 }
 
 void ObjectStats::RecordVirtualObjectStats(VirtualInstanceType type,
-                                           size_t size) {
+                                           size_t size, size_t over_allocated) {
   DCHECK_LE(type, LAST_VIRTUAL_TYPE);
   object_counts_[FIRST_VIRTUAL_TYPE + type]++;
   object_sizes_[FIRST_VIRTUAL_TYPE + type] += size;
   size_histogram_[FIRST_VIRTUAL_TYPE + type][HistogramIndexFromSize(size)]++;
-}
-
-void ObjectStats::RecordCodeSubTypeStats(int code_sub_type, size_t size) {
-  int code_sub_type_index = FIRST_CODE_KIND_SUB_TYPE + code_sub_type;
-  DCHECK_GE(code_sub_type_index, FIRST_CODE_KIND_SUB_TYPE);
-  DCHECK_LT(code_sub_type_index, FIRST_FIXED_ARRAY_SUB_TYPE);
-  object_counts_[code_sub_type_index]++;
-  object_sizes_[code_sub_type_index] += size;
-  size_histogram_[code_sub_type_index][HistogramIndexFromSize(size)]++;
-}
-
-bool ObjectStats::RecordFixedArraySubTypeStats(FixedArrayBase* array,
-                                               int array_sub_type, size_t size,
-                                               size_t over_allocated) {
-  auto it = visited_fixed_array_sub_types_.insert(array);
-  if (!it.second) return false;
-  DCHECK_LE(array_sub_type, LAST_FIXED_ARRAY_SUB_TYPE);
-  object_counts_[FIRST_FIXED_ARRAY_SUB_TYPE + array_sub_type]++;
-  object_sizes_[FIRST_FIXED_ARRAY_SUB_TYPE + array_sub_type] += size;
-  size_histogram_[FIRST_FIXED_ARRAY_SUB_TYPE + array_sub_type]
-                 [HistogramIndexFromSize(size)]++;
-  if (over_allocated > 0) {
-    InstanceType type =
-        array->IsHashTable() ? HASH_TABLE_TYPE : FIXED_ARRAY_TYPE;
-    over_allocated_[FIRST_FIXED_ARRAY_SUB_TYPE + array_sub_type] +=
-        over_allocated;
-    over_allocated_histogram_[FIRST_FIXED_ARRAY_SUB_TYPE + array_sub_type]
-                             [HistogramIndexFromSize(over_allocated)]++;
-    over_allocated_[type] += over_allocated;
-    over_allocated_histogram_[type][HistogramIndexFromSize(over_allocated)]++;
-  }
-  return true;
+  over_allocated_[FIRST_VIRTUAL_TYPE + type] += over_allocated;
+  over_allocated_histogram_[FIRST_VIRTUAL_TYPE + type]
+                           [HistogramIndexFromSize(size)]++;
 }
 
 Isolate* ObjectStats::isolate() { return heap()->isolate(); }
 
 class ObjectStatsCollectorImpl {
  public:
+  enum Phase {
+    kPhase1,
+    kPhase2,
+  };
+  static const int kNumberOfPhases = kPhase2 + 1;
+
   ObjectStatsCollectorImpl(Heap* heap, ObjectStats* stats);
 
   void CollectGlobalStatistics();
+  void CollectStatistics(HeapObject* obj, Phase phase);
 
-  // Collects statistics of objects for virtual instance types.
-  void CollectVirtualStatistics(HeapObject* obj);
+ private:
+  enum CowMode {
+    kCheckCow,
+    kIgnoreCow,
+  };
 
-  // Collects statistics of objects for regular instance types.
-  void CollectStatistics(HeapObject* obj);
+  Isolate* isolate() { return heap_->isolate(); }
 
- private:
-  class CompilationCacheTableVisitor;
+  bool RecordVirtualObjectStats(HeapObject* parent, HeapObject* obj,
+                                ObjectStats::VirtualInstanceType type,
+                                size_t size, size_t over_allocated,
+                                CowMode check_cow_array = kCheckCow);
+  // Gets size from |ob| and assumes no over allocating.
+  bool RecordSimpleVirtualObjectStats(HeapObject* parent, HeapObject* obj,
+                                      ObjectStats::VirtualInstanceType type);
+  // For HashTable it is possible to compute over allocated memory.
+  void RecordHashTableVirtualObjectStats(HeapObject* parent,
+                                         FixedArray* hash_table,
+                                         ObjectStats::VirtualInstanceType type);
 
-  void RecordObjectStats(HeapObject* obj, InstanceType type, size_t size);
-  void RecordBytecodeArrayDetails(BytecodeArray* obj);
-  void RecordCodeDetails(Code* code);
-  void RecordFixedArrayDetails(FixedArray* array);
-  void RecordJSCollectionDetails(JSObject* obj);
-  void RecordJSObjectDetails(JSObject* object);
-  void RecordJSWeakCollectionDetails(JSWeakCollection* obj);
-  void RecordMapDetails(Map* map);
-  void RecordScriptDetails(Script* obj);
-  void RecordTemplateInfoDetails(TemplateInfo* obj);
-  void RecordSharedFunctionInfoDetails(SharedFunctionInfo* sfi);
-
-  bool RecordFixedArrayHelper(HeapObject* parent, FixedArray* array,
-                              int subtype, size_t overhead);
-  void RecursivelyRecordFixedArrayHelper(HeapObject* parent, FixedArray* array,
-                                         int subtype);
-  template <class HashTable>
-  void RecordHashTableHelper(HeapObject* parent, HashTable* array, int subtype);
   bool SameLiveness(HeapObject* obj1, HeapObject* obj2);
+  bool CanRecordFixedArray(FixedArrayBase* array);
+  bool IsCowArray(FixedArrayBase* array);
 
-  void RecordVirtualObjectStats(HeapObject* obj,
-                                ObjectStats::VirtualInstanceType type,
-                                size_t size);
+  // Blacklist for objects that should not be recorded using
+  // VirtualObjectStats and RecordSimpleVirtualObjectStats. For recording those
+  // objects dispatch to the low level ObjectStats::RecordObjectStats manually.
+  bool ShouldRecordObject(HeapObject* object, CowMode check_cow_array);
+
+  void RecordObjectStats(HeapObject* obj, InstanceType type, size_t size);
+
+  // Specific recursion into constant pool or embedded code objects. Records
+  // FixedArrays and Tuple2 that look like ConstantElementsPair.
+  void RecordVirtualObjectsForConstantPoolOrEmbeddedObjects(
+      HeapObject* parent, HeapObject* object,
+      ObjectStats::VirtualInstanceType type);
+
+  // Details.
   void RecordVirtualAllocationSiteDetails(AllocationSite* site);
+  void RecordVirtualBytecodeArrayDetails(BytecodeArray* bytecode);
+  void RecordVirtualCodeDetails(Code* code);
+  void RecordVirtualContext(Context* context);
+  void RecordVirtualFeedbackVectorDetails(FeedbackVector* vector);
+  void RecordVirtualFixedArrayDetails(FixedArray* array);
+  void RecordVirtualFunctionTemplateInfoDetails(FunctionTemplateInfo* fti);
+  void RecordVirtualJSGlobalObjectDetails(JSGlobalObject* object);
+  void RecordVirtualJSCollectionDetails(JSObject* object);
+  void RecordVirtualJSObjectDetails(JSObject* object);
+  void RecordVirtualMapDetails(Map* map);
+  void RecordVirtualScriptDetails(Script* script);
+  void RecordVirtualSharedFunctionInfoDetails(SharedFunctionInfo* info);
+  void RecordVirtualJSFunctionDetails(JSFunction* function);
 
   Heap* heap_;
   ObjectStats* stats_;
   MarkCompactCollector::NonAtomicMarkingState* marking_state_;
   std::unordered_set<HeapObject*> virtual_objects_;
-
-  friend class ObjectStatsCollectorImpl::CompilationCacheTableVisitor;
 };
 
 ObjectStatsCollectorImpl::ObjectStatsCollectorImpl(Heap* heap,
@@ -298,18 +275,45 @@ ObjectStatsCollectorImpl::ObjectStatsCollectorImpl(Heap* heap,
       marking_state_(
           heap->mark_compact_collector()->non_atomic_marking_state()) {}
 
-// For entries which shared the same instance type (historically FixedArrays)
-// we do a pre-pass and create virtual instance types.
-void ObjectStatsCollectorImpl::CollectVirtualStatistics(HeapObject* obj) {
-  if (obj->IsAllocationSite()) {
-    RecordVirtualAllocationSiteDetails(AllocationSite::cast(obj));
+bool ObjectStatsCollectorImpl::ShouldRecordObject(HeapObject* obj,
+                                                  CowMode check_cow_array) {
+  if (obj->IsFixedArray()) {
+    FixedArray* fixed_array = FixedArray::cast(obj);
+    bool cow_check = check_cow_array == kIgnoreCow || !IsCowArray(fixed_array);
+    return CanRecordFixedArray(fixed_array) && cow_check;
   }
+  if (obj == heap_->empty_property_array()) return false;
+  return true;
+}
+
+void ObjectStatsCollectorImpl::RecordHashTableVirtualObjectStats(
+    HeapObject* parent, FixedArray* hash_table,
+    ObjectStats::VirtualInstanceType type) {
+  CHECK(hash_table->IsHashTable());
+  // TODO(mlippautz): Implement over allocation for hash tables.
+  RecordVirtualObjectStats(parent, hash_table, type, hash_table->Size(),
+                           ObjectStats::kNoOverAllocation);
 }
 
-void ObjectStatsCollectorImpl::RecordVirtualObjectStats(
-    HeapObject* obj, ObjectStats::VirtualInstanceType type, size_t size) {
-  virtual_objects_.insert(obj);
-  stats_->RecordVirtualObjectStats(type, size);
+bool ObjectStatsCollectorImpl::RecordSimpleVirtualObjectStats(
+    HeapObject* parent, HeapObject* obj,
+    ObjectStats::VirtualInstanceType type) {
+  return RecordVirtualObjectStats(parent, obj, type, obj->Size(),
+                                  ObjectStats::kNoOverAllocation, kCheckCow);
+}
+
+bool ObjectStatsCollectorImpl::RecordVirtualObjectStats(
+    HeapObject* parent, HeapObject* obj, ObjectStats::VirtualInstanceType type,
+    size_t size, size_t over_allocated, CowMode check_cow_array) {
+  if (!SameLiveness(parent, obj) || !ShouldRecordObject(obj, check_cow_array))
+    return false;
+
+  if (virtual_objects_.find(obj) == virtual_objects_.end()) {
+    virtual_objects_.insert(obj);
+    stats_->RecordVirtualObjectStats(type, size, over_allocated);
+    return true;
+  }
+  return false;
 }
 
 void ObjectStatsCollectorImpl::RecordVirtualAllocationSiteDetails(
@@ -317,141 +321,290 @@ void ObjectStatsCollectorImpl::RecordVirtualAllocationSiteDetails(
   if (!site->PointsToLiteral()) return;
   JSObject* boilerplate = site->boilerplate();
   if (boilerplate->IsJSArray()) {
-    RecordVirtualObjectStats(boilerplate,
-                             ObjectStats::JS_ARRAY_BOILERPLATE_TYPE,
-                             boilerplate->Size());
+    RecordSimpleVirtualObjectStats(site, boilerplate,
+                                   ObjectStats::JS_ARRAY_BOILERPLATE_TYPE);
     // Array boilerplates cannot have properties.
   } else {
-    RecordVirtualObjectStats(boilerplate,
-                             ObjectStats::JS_OBJECT_BOILERPLATE_TYPE,
-                             boilerplate->Size());
+    RecordVirtualObjectStats(
+        site, boilerplate, ObjectStats::JS_OBJECT_BOILERPLATE_TYPE,
+        boilerplate->Size(), ObjectStats::kNoOverAllocation);
     if (boilerplate->HasFastProperties()) {
-      // We'll misclassify the empty_proeprty_array here. Given that there is a
-      // single instance, this is neglible.
+      // We'll mis-classify the empty_property_array here. Given that there is a
+      // single instance, this is negligible.
       PropertyArray* properties = boilerplate->property_array();
-      RecordVirtualObjectStats(properties,
-                               ObjectStats::BOILERPLATE_PROPERTY_ARRAY_TYPE,
-                               properties->Size());
+      RecordSimpleVirtualObjectStats(
+          site, properties, ObjectStats::BOILERPLATE_PROPERTY_ARRAY_TYPE);
     } else {
       NameDictionary* properties = boilerplate->property_dictionary();
-      RecordVirtualObjectStats(properties,
-                               ObjectStats::BOILERPLATE_NAME_DICTIONARY_TYPE,
-                               properties->Size());
+      RecordSimpleVirtualObjectStats(
+          site, properties, ObjectStats::BOILERPLATE_PROPERTY_DICTIONARY_TYPE);
     }
   }
   FixedArrayBase* elements = boilerplate->elements();
-  // We skip COW elements since they are shared, and we are sure that if the
-  // boilerplate exists there must have been at least one instantiation.
-  if (!elements->IsCowArray()) {
-    RecordVirtualObjectStats(elements, ObjectStats::BOILERPLATE_ELEMENTS_TYPE,
-                             elements->Size());
-  }
+  RecordSimpleVirtualObjectStats(site, elements,
+                                 ObjectStats::BOILERPLATE_ELEMENTS_TYPE);
 }
 
-void ObjectStatsCollectorImpl::CollectStatistics(HeapObject* obj) {
-  Map* map = obj->map();
-
-  // Record for the InstanceType.
-  int object_size = obj->Size();
-  RecordObjectStats(obj, map->instance_type(), object_size);
-
-  // Record specific sub types where possible.
-  if (obj->IsMap()) RecordMapDetails(Map::cast(obj));
-  if (obj->IsObjectTemplateInfo() || obj->IsFunctionTemplateInfo()) {
-    RecordTemplateInfoDetails(TemplateInfo::cast(obj));
+void ObjectStatsCollectorImpl::RecordVirtualFunctionTemplateInfoDetails(
+    FunctionTemplateInfo* fti) {
+  // named_property_handler and indexed_property_handler are recorded as
+  // INTERCEPTOR_INFO_TYPE.
+  if (!fti->call_code()->IsUndefined(isolate())) {
+    RecordSimpleVirtualObjectStats(
+        fti, CallHandlerInfo::cast(fti->call_code()),
+        ObjectStats::FUNCTION_TEMPLATE_INFO_ENTRIES_TYPE);
   }
-  if (obj->IsBytecodeArray()) {
-    RecordBytecodeArrayDetails(BytecodeArray::cast(obj));
+  if (!fti->instance_call_handler()->IsUndefined(isolate())) {
+    RecordSimpleVirtualObjectStats(
+        fti, CallHandlerInfo::cast(fti->instance_call_handler()),
+        ObjectStats::FUNCTION_TEMPLATE_INFO_ENTRIES_TYPE);
   }
-  if (obj->IsCode()) RecordCodeDetails(Code::cast(obj));
-  if (obj->IsSharedFunctionInfo()) {
-    RecordSharedFunctionInfoDetails(SharedFunctionInfo::cast(obj));
+}
+
+void ObjectStatsCollectorImpl::RecordVirtualJSGlobalObjectDetails(
+    JSGlobalObject* object) {
+  // Properties.
+  GlobalDictionary* properties = object->global_dictionary();
+  RecordHashTableVirtualObjectStats(object, properties,
+                                    ObjectStats::GLOBAL_PROPERTIES_TYPE);
+  // Elements.
+  FixedArrayBase* elements = object->elements();
+  RecordSimpleVirtualObjectStats(object, elements,
+                                 ObjectStats::GLOBAL_ELEMENTS_TYPE);
+}
+
+void ObjectStatsCollectorImpl::RecordVirtualJSCollectionDetails(
+    JSObject* object) {
+  if (object->IsJSMap()) {
+    RecordSimpleVirtualObjectStats(
+        object, FixedArray::cast(JSMap::cast(object)->table()),
+        ObjectStats::JS_COLLETION_TABLE_TYPE);
   }
-  if (obj->IsFixedArray()) RecordFixedArrayDetails(FixedArray::cast(obj));
-  if (obj->IsJSObject()) RecordJSObjectDetails(JSObject::cast(obj));
-  if (obj->IsJSWeakCollection()) {
-    RecordJSWeakCollectionDetails(JSWeakCollection::cast(obj));
+  if (object->IsJSSet()) {
+    RecordSimpleVirtualObjectStats(
+        object, FixedArray::cast(JSSet::cast(object)->table()),
+        ObjectStats::JS_COLLETION_TABLE_TYPE);
   }
-  if (obj->IsJSCollection()) {
-    RecordJSCollectionDetails(JSObject::cast(obj));
+}
+
+void ObjectStatsCollectorImpl::RecordVirtualJSObjectDetails(JSObject* object) {
+  // JSGlobalObject is recorded separately.
+  if (object->IsJSGlobalObject()) return;
+
+  // Properties.
+  if (object->HasFastProperties()) {
+    PropertyArray* properties = object->property_array();
+    CHECK_EQ(PROPERTY_ARRAY_TYPE, properties->map()->instance_type());
+  } else {
+    NameDictionary* properties = object->property_dictionary();
+    RecordHashTableVirtualObjectStats(
+        object, properties, ObjectStats::OBJECT_PROPERTY_DICTIONARY_TYPE);
   }
-  if (obj->IsScript()) RecordScriptDetails(Script::cast(obj));
+  // Elements.
+  FixedArrayBase* elements = object->elements();
+  RecordSimpleVirtualObjectStats(object, elements, ObjectStats::ELEMENTS_TYPE);
 }
 
-class ObjectStatsCollectorImpl::CompilationCacheTableVisitor
-    : public RootVisitor {
- public:
-  explicit CompilationCacheTableVisitor(ObjectStatsCollectorImpl* parent)
-      : parent_(parent) {}
-
-  void VisitRootPointers(Root root, Object** start, Object** end) override {
-    for (Object** current = start; current < end; current++) {
-      HeapObject* obj = HeapObject::cast(*current);
-      if (obj->IsUndefined(parent_->heap_->isolate())) continue;
-      CHECK(obj->IsCompilationCacheTable());
-      parent_->RecordHashTableHelper(nullptr, CompilationCacheTable::cast(obj),
-                                     COMPILATION_CACHE_TABLE_SUB_TYPE);
+static ObjectStats::VirtualInstanceType GetFeedbackSlotType(
+    Object* obj, FeedbackSlotKind kind, Isolate* isolate) {
+  switch (kind) {
+    case FeedbackSlotKind::kCall:
+      if (obj == *isolate->factory()->uninitialized_symbol() ||
+          obj == *isolate->factory()->premonomorphic_symbol()) {
+        return ObjectStats::FEEDBACK_VECTOR_SLOT_CALL_UNUSED_TYPE;
+      }
+      return ObjectStats::FEEDBACK_VECTOR_SLOT_CALL_TYPE;
+
+    case FeedbackSlotKind::kLoadProperty:
+    case FeedbackSlotKind::kLoadGlobalInsideTypeof:
+    case FeedbackSlotKind::kLoadGlobalNotInsideTypeof:
+    case FeedbackSlotKind::kLoadKeyed:
+      if (obj == *isolate->factory()->uninitialized_symbol() ||
+          obj == *isolate->factory()->premonomorphic_symbol()) {
+        return ObjectStats::FEEDBACK_VECTOR_SLOT_LOAD_UNUSED_TYPE;
+      }
+      return ObjectStats::FEEDBACK_VECTOR_SLOT_LOAD_TYPE;
+
+    case FeedbackSlotKind::kStoreNamedSloppy:
+    case FeedbackSlotKind::kStoreNamedStrict:
+    case FeedbackSlotKind::kStoreOwnNamed:
+    case FeedbackSlotKind::kStoreGlobalSloppy:
+    case FeedbackSlotKind::kStoreGlobalStrict:
+    case FeedbackSlotKind::kStoreKeyedSloppy:
+    case FeedbackSlotKind::kStoreKeyedStrict:
+      if (obj == *isolate->factory()->uninitialized_symbol() ||
+          obj == *isolate->factory()->premonomorphic_symbol()) {
+        return ObjectStats::FEEDBACK_VECTOR_SLOT_STORE_UNUSED_TYPE;
+      }
+      return ObjectStats::FEEDBACK_VECTOR_SLOT_STORE_TYPE;
+
+    case FeedbackSlotKind::kBinaryOp:
+    case FeedbackSlotKind::kCompareOp:
+      return ObjectStats::FEEDBACK_VECTOR_SLOT_ENUM_TYPE;
+
+    default:
+      return ObjectStats::FEEDBACK_VECTOR_SLOT_OTHER_TYPE;
+  }
+}
+
+void ObjectStatsCollectorImpl::RecordVirtualFeedbackVectorDetails(
+    FeedbackVector* vector) {
+  if (virtual_objects_.find(vector) == virtual_objects_.end()) {
+    // Manually insert the feedback vector into the virtual object list, since
+    // we're logging its component parts separately.
+    virtual_objects_.insert(vector);
+
+    size_t calculated_size = 0;
+
+    // Log the feedback vector's header (fixed fields).
+    size_t header_size =
+        reinterpret_cast<Address>(vector->slots_start()) - vector->address();
+    stats_->RecordVirtualObjectStats(ObjectStats::FEEDBACK_VECTOR_HEADER_TYPE,
+                                     header_size,
+                                     ObjectStats::kNoOverAllocation);
+    calculated_size += header_size;
+
+    // Iterate over the feedback slots and log each one.
+    FeedbackMetadataIterator it(vector->metadata());
+    while (it.HasNext()) {
+      FeedbackSlot slot = it.Next();
+      // Log the entry (or entries) taken up by this slot.
+      size_t slot_size = it.entry_size() * kPointerSize;
+      stats_->RecordVirtualObjectStats(
+          GetFeedbackSlotType(vector->Get(slot), it.kind(), heap_->isolate()),
+          slot_size, ObjectStats::kNoOverAllocation);
+      calculated_size += slot_size;
+
+      // Log the monomorphic/polymorphic helper objects that this slot owns.
+      for (int i = 0; i < it.entry_size(); i++) {
+        Object* raw_object = vector->get(slot.ToInt() + i);
+        if (!raw_object->IsHeapObject()) continue;
+        HeapObject* object = HeapObject::cast(raw_object);
+        if (object->IsCell() || object->IsFixedArray()) {
+          RecordSimpleVirtualObjectStats(
+              vector, object, ObjectStats::FEEDBACK_VECTOR_ENTRY_TYPE);
+        }
+      }
     }
+
+    CHECK_EQ(calculated_size, vector->Size());
   }
+}
 
- private:
-  ObjectStatsCollectorImpl* parent_;
-};
+void ObjectStatsCollectorImpl::RecordVirtualFixedArrayDetails(
+    FixedArray* array) {
+  if (IsCowArray(array)) {
+    RecordVirtualObjectStats(nullptr, array, ObjectStats::COW_ARRAY_TYPE,
+                             array->Size(), ObjectStats::kNoOverAllocation,
+                             kIgnoreCow);
+  }
+}
+
+void ObjectStatsCollectorImpl::CollectStatistics(HeapObject* obj, Phase phase) {
+  Map* map = obj->map();
+  switch (phase) {
+    case kPhase1:
+      if (obj->IsFeedbackVector()) {
+        RecordVirtualFeedbackVectorDetails(FeedbackVector::cast(obj));
+      } else if (obj->IsMap()) {
+        RecordVirtualMapDetails(Map::cast(obj));
+      } else if (obj->IsBytecodeArray()) {
+        RecordVirtualBytecodeArrayDetails(BytecodeArray::cast(obj));
+      } else if (obj->IsCode()) {
+        RecordVirtualCodeDetails(Code::cast(obj));
+      } else if (obj->IsFunctionTemplateInfo()) {
+        RecordVirtualFunctionTemplateInfoDetails(
+            FunctionTemplateInfo::cast(obj));
+      } else if (obj->IsJSFunction()) {
+        RecordVirtualJSFunctionDetails(JSFunction::cast(obj));
+      } else if (obj->IsJSGlobalObject()) {
+        RecordVirtualJSGlobalObjectDetails(JSGlobalObject::cast(obj));
+      } else if (obj->IsJSObject()) {
+        // This phase needs to come after RecordVirtualAllocationSiteDetails
+        // to properly split among boilerplates.
+        RecordVirtualJSObjectDetails(JSObject::cast(obj));
+      } else if (obj->IsJSCollection()) {
+        RecordVirtualJSCollectionDetails(JSObject::cast(obj));
+      } else if (obj->IsSharedFunctionInfo()) {
+        RecordVirtualSharedFunctionInfoDetails(SharedFunctionInfo::cast(obj));
+      } else if (obj->IsContext()) {
+        RecordVirtualContext(Context::cast(obj));
+      } else if (obj->IsScript()) {
+        RecordVirtualScriptDetails(Script::cast(obj));
+      } else if (obj->IsFixedArray()) {
+        // Has to go last as it triggers too eagerly.
+        RecordVirtualFixedArrayDetails(FixedArray::cast(obj));
+      }
+      break;
+    case kPhase2:
+      RecordObjectStats(obj, map->instance_type(), obj->Size());
+      break;
+  }
+}
 
 void ObjectStatsCollectorImpl::CollectGlobalStatistics() {
-  // Global FixedArrays.
-  RecordFixedArrayHelper(nullptr, heap_->weak_new_space_object_to_code_list(),
-                         WEAK_NEW_SPACE_OBJECT_TO_CODE_SUB_TYPE, 0);
-  RecordFixedArrayHelper(nullptr, heap_->serialized_objects(),
-                         SERIALIZED_OBJECTS_SUB_TYPE, 0);
-  RecordFixedArrayHelper(nullptr, heap_->number_string_cache(),
-                         NUMBER_STRING_CACHE_SUB_TYPE, 0);
-  RecordFixedArrayHelper(nullptr, heap_->single_character_string_cache(),
-                         SINGLE_CHARACTER_STRING_CACHE_SUB_TYPE, 0);
-  RecordFixedArrayHelper(nullptr, heap_->string_split_cache(),
-                         STRING_SPLIT_CACHE_SUB_TYPE, 0);
-  RecordFixedArrayHelper(nullptr, heap_->regexp_multiple_cache(),
-                         REGEXP_MULTIPLE_CACHE_SUB_TYPE, 0);
-  RecordFixedArrayHelper(nullptr, heap_->retained_maps(),
-                         RETAINED_MAPS_SUB_TYPE, 0);
-
-  // Global weak FixedArrays.
-  RecordFixedArrayHelper(
+  // Iterate boilerplates first to disambiguate them from regular JS objects.
+  Object* list = heap_->allocation_sites_list();
+  while (list->IsAllocationSite()) {
+    AllocationSite* site = AllocationSite::cast(list);
+    RecordVirtualAllocationSiteDetails(site);
+    list = site->weak_next();
+  }
+
+  // FixedArray.
+  RecordSimpleVirtualObjectStats(
+      nullptr, heap_->weak_new_space_object_to_code_list(),
+      ObjectStats::WEAK_NEW_SPACE_OBJECT_TO_CODE_TYPE);
+  RecordSimpleVirtualObjectStats(nullptr, heap_->serialized_objects(),
+                                 ObjectStats::SERIALIZED_OBJECTS_TYPE);
+  RecordSimpleVirtualObjectStats(nullptr, heap_->number_string_cache(),
+                                 ObjectStats::NUMBER_STRING_CACHE_TYPE);
+  RecordSimpleVirtualObjectStats(
+      nullptr, heap_->single_character_string_cache(),
+      ObjectStats::SINGLE_CHARACTER_STRING_CACHE_TYPE);
+  RecordSimpleVirtualObjectStats(nullptr, heap_->string_split_cache(),
+                                 ObjectStats::STRING_SPLIT_CACHE_TYPE);
+  RecordSimpleVirtualObjectStats(nullptr, heap_->regexp_multiple_cache(),
+                                 ObjectStats::REGEXP_MULTIPLE_CACHE_TYPE);
+  RecordSimpleVirtualObjectStats(nullptr, heap_->retained_maps(),
+                                 ObjectStats::RETAINED_MAPS_TYPE);
+
+  // WeakFixedArray.
+  RecordSimpleVirtualObjectStats(
       nullptr, WeakFixedArray::cast(heap_->noscript_shared_function_infos()),
-      NOSCRIPT_SHARED_FUNCTION_INFOS_SUB_TYPE, 0);
-  RecordFixedArrayHelper(nullptr, WeakFixedArray::cast(heap_->script_list()),
-                         SCRIPT_LIST_SUB_TYPE, 0);
-
-  // Global hash tables.
-  RecordHashTableHelper(nullptr, heap_->string_table(), STRING_TABLE_SUB_TYPE);
-  RecordHashTableHelper(nullptr, heap_->weak_object_to_code_table(),
-                        OBJECT_TO_CODE_SUB_TYPE);
-  RecordHashTableHelper(nullptr, heap_->code_stubs(),
-                        CODE_STUBS_TABLE_SUB_TYPE);
-  RecordHashTableHelper(nullptr, heap_->empty_property_dictionary(),
-                        EMPTY_PROPERTIES_DICTIONARY_SUB_TYPE);
-  CompilationCache* compilation_cache = heap_->isolate()->compilation_cache();
-  CompilationCacheTableVisitor v(this);
-  compilation_cache->Iterate(&v);
+      ObjectStats::NOSCRIPT_SHARED_FUNCTION_INFOS_TYPE);
+  RecordSimpleVirtualObjectStats(nullptr,
+                                 WeakFixedArray::cast(heap_->script_list()),
+                                 ObjectStats::SCRIPT_LIST_TYPE);
+
+  // HashTable.
+  RecordHashTableVirtualObjectStats(nullptr, heap_->string_table(),
+                                    ObjectStats::STRING_TABLE_TYPE);
+  RecordHashTableVirtualObjectStats(nullptr, heap_->code_stubs(),
+                                    ObjectStats::CODE_STUBS_TABLE_TYPE);
+
+  // WeakHashTable.
+  RecordHashTableVirtualObjectStats(nullptr, heap_->weak_object_to_code_table(),
+                                    ObjectStats::OBJECT_TO_CODE_TYPE);
 }
 
 void ObjectStatsCollectorImpl::RecordObjectStats(HeapObject* obj,
                                                  InstanceType type,
                                                  size_t size) {
-  if (virtual_objects_.find(obj) == virtual_objects_.end())
+  if (virtual_objects_.find(obj) == virtual_objects_.end()) {
     stats_->RecordObjectStats(type, size);
+  }
 }
 
-static bool CanRecordFixedArray(Heap* heap, FixedArrayBase* array) {
-  return array->map()->instance_type() == FIXED_ARRAY_TYPE &&
-         array != heap->empty_fixed_array() &&
-         array != heap->empty_sloppy_arguments_elements() &&
-         array != heap->empty_slow_element_dictionary() &&
-         array != heap->empty_property_dictionary();
+bool ObjectStatsCollectorImpl::CanRecordFixedArray(FixedArrayBase* array) {
+  return array != heap_->empty_fixed_array() &&
+         array != heap_->empty_sloppy_arguments_elements() &&
+         array != heap_->empty_slow_element_dictionary() &&
+         array != heap_->empty_property_dictionary();
 }
 
-static bool IsCowArray(Heap* heap, FixedArrayBase* array) {
-  return array->map() == heap->fixed_cow_array_map();
+bool ObjectStatsCollectorImpl::IsCowArray(FixedArrayBase* array) {
+  return array->map() == heap_->fixed_cow_array_map();
 }
 
 bool ObjectStatsCollectorImpl::SameLiveness(HeapObject* obj1,
@@ -460,256 +613,226 @@ bool ObjectStatsCollectorImpl::SameLiveness(HeapObject* obj1,
          marking_state_->Color(obj1) == marking_state_->Color(obj2);
 }
 
-bool ObjectStatsCollectorImpl::RecordFixedArrayHelper(HeapObject* parent,
-                                                      FixedArray* array,
-                                                      int subtype,
-                                                      size_t overhead) {
-  if (SameLiveness(parent, array) && CanRecordFixedArray(heap_, array) &&
-      !IsCowArray(heap_, array)) {
-    return stats_->RecordFixedArraySubTypeStats(array, subtype, array->Size(),
-                                                overhead);
+void ObjectStatsCollectorImpl::RecordVirtualMapDetails(Map* map) {
+  // TODO(mlippautz): map->dependent_code(): DEPENDENT_CODE_TYPE.
+
+  DescriptorArray* array = map->instance_descriptors();
+  if (map->owns_descriptors() && array != heap_->empty_descriptor_array()) {
+    // DescriptorArray has its own instance type.
+    EnumCache* enum_cache = array->GetEnumCache();
+    RecordSimpleVirtualObjectStats(array, enum_cache->keys(),
+                                   ObjectStats::ENUM_CACHE_TYPE);
+    RecordSimpleVirtualObjectStats(array, enum_cache->indices(),
+                                   ObjectStats::ENUM_INDICES_CACHE_TYPE);
   }
-  return false;
-}
 
-void ObjectStatsCollectorImpl::RecursivelyRecordFixedArrayHelper(
-    HeapObject* parent, FixedArray* array, int subtype) {
-  if (RecordFixedArrayHelper(parent, array, subtype, 0)) {
-    for (int i = 0; i < array->length(); i++) {
-      if (array->get(i)->IsFixedArray()) {
-        RecursivelyRecordFixedArrayHelper(
-            parent, FixedArray::cast(array->get(i)), subtype);
+  if (map->is_prototype_map()) {
+    if (map->prototype_info()->IsPrototypeInfo()) {
+      PrototypeInfo* info = PrototypeInfo::cast(map->prototype_info());
+      Object* users = info->prototype_users();
+      if (users->IsWeakFixedArray()) {
+        RecordSimpleVirtualObjectStats(map, WeakFixedArray::cast(users),
+                                       ObjectStats::PROTOTYPE_USERS_TYPE);
       }
     }
   }
 }
 
-template <class HashTable>
-void ObjectStatsCollectorImpl::RecordHashTableHelper(HeapObject* parent,
-                                                     HashTable* array,
-                                                     int subtype) {
-  int used = array->NumberOfElements() * HashTable::kEntrySize * kPointerSize;
-  CHECK_GE(array->Size(), used);
-  size_t overhead = array->Size() - used -
-                    HashTable::kElementsStartIndex * kPointerSize -
-                    FixedArray::kHeaderSize;
-  RecordFixedArrayHelper(parent, array, subtype, overhead);
-}
-
-void ObjectStatsCollectorImpl::RecordJSObjectDetails(JSObject* object) {
-  size_t overhead = 0;
-  FixedArrayBase* elements = object->elements();
-  if (CanRecordFixedArray(heap_, elements) && !IsCowArray(heap_, elements)) {
-    if (elements->IsDictionary() && SameLiveness(object, elements)) {
-      NumberDictionary* dict = NumberDictionary::cast(elements);
-      RecordHashTableHelper(object, dict, DICTIONARY_ELEMENTS_SUB_TYPE);
-    } else {
-      if (IsHoleyElementsKind(object->GetElementsKind())) {
-        int used = object->GetFastElementsUsage() * kPointerSize;
-        if (object->GetElementsKind() == HOLEY_DOUBLE_ELEMENTS) used *= 2;
-        CHECK_GE(elements->Size(), used);
-        overhead = elements->Size() - used - FixedArray::kHeaderSize;
-      }
-      stats_->RecordFixedArraySubTypeStats(elements, PACKED_ELEMENTS_SUB_TYPE,
-                                           elements->Size(), overhead);
+void ObjectStatsCollectorImpl::RecordVirtualScriptDetails(Script* script) {
+  FixedArray* infos = script->shared_function_infos();
+  RecordSimpleVirtualObjectStats(
+      script, script->shared_function_infos(),
+      ObjectStats::SCRIPT_SHARED_FUNCTION_INFOS_TYPE);
+  // Split off weak cells from the regular weak cell type.
+  for (int i = 0; i < infos->length(); i++) {
+    if (infos->get(i)->IsWeakCell()) {
+      RecordSimpleVirtualObjectStats(
+          infos, WeakCell::cast(infos->get(i)),
+          ObjectStats::SCRIPT_SHARED_FUNCTION_INFOS_TYPE);
     }
   }
 
-  if (object->IsJSGlobalObject()) {
-    GlobalDictionary* properties =
-        JSGlobalObject::cast(object)->global_dictionary();
-    if (CanRecordFixedArray(heap_, properties) &&
-        SameLiveness(object, properties)) {
-      RecordHashTableHelper(object, properties, DICTIONARY_PROPERTIES_SUB_TYPE);
-    }
-  } else if (!object->HasFastProperties()) {
-    NameDictionary* properties = object->property_dictionary();
-    if (CanRecordFixedArray(heap_, properties) &&
-        SameLiveness(object, properties)) {
-      RecordHashTableHelper(object, properties, DICTIONARY_PROPERTIES_SUB_TYPE);
-    }
+  // Log the size of external source code.
+  Object* source = script->source();
+  if (source->IsExternalString()) {
+    // The contents of external strings aren't on the heap, so we have to record
+    // them manually.
+    ExternalString* external_source_string = ExternalString::cast(source);
+    size_t length_multiplier = external_source_string->IsTwoByteRepresentation()
+                                   ? kShortSize
+                                   : kCharSize;
+    size_t off_heap_size = external_source_string->length() * length_multiplier;
+    size_t on_heap_size = external_source_string->Size();
+    RecordVirtualObjectStats(script, external_source_string,
+                             ObjectStats::SCRIPT_SOURCE_EXTERNAL_TYPE,
+                             on_heap_size + off_heap_size,
+                             ObjectStats::kNoOverAllocation);
+  } else if (source->IsHeapObject()) {
+    RecordSimpleVirtualObjectStats(
+        script, HeapObject::cast(source),
+        ObjectStats::SCRIPT_SOURCE_NON_EXTERNAL_TYPE);
   }
 }
 
-void ObjectStatsCollectorImpl::RecordJSWeakCollectionDetails(
-    JSWeakCollection* obj) {
-  if (obj->table()->IsHashTable()) {
-    ObjectHashTable* table = ObjectHashTable::cast(obj->table());
-    int used = table->NumberOfElements() * ObjectHashTable::kEntrySize;
-    size_t overhead = table->Size() - used;
-    RecordFixedArrayHelper(obj, table, JS_WEAK_COLLECTION_SUB_TYPE, overhead);
+void ObjectStatsCollectorImpl::RecordVirtualSharedFunctionInfoDetails(
+    SharedFunctionInfo* info) {
+  // Uncompiled SharedFunctionInfo gets its own category.
+  if (!info->is_compiled()) {
+    RecordSimpleVirtualObjectStats(
+        nullptr, info, ObjectStats::UNCOMPILED_SHARED_FUNCTION_INFO_TYPE);
   }
+  // SharedFunctonInfo::feedback_metadata() is a COW array.
+  FeedbackMetadata* fm = FeedbackMetadata::cast(info->feedback_metadata());
+  RecordVirtualObjectStats(info, fm, ObjectStats::FEEDBACK_METADATA_TYPE,
+                           fm->Size(), ObjectStats::kNoOverAllocation,
+                           kIgnoreCow);
 }
 
-void ObjectStatsCollectorImpl::RecordJSCollectionDetails(JSObject* obj) {
-  // The JS versions use a different HashTable implementation that cannot use
-  // the regular helper. Since overall impact is usually small just record
-  // without overhead.
-  if (obj->IsJSMap()) {
-    RecordFixedArrayHelper(nullptr, FixedArray::cast(JSMap::cast(obj)->table()),
-                           JS_COLLECTION_SUB_TYPE, 0);
-  }
-  if (obj->IsJSSet()) {
-    RecordFixedArrayHelper(nullptr, FixedArray::cast(JSSet::cast(obj)->table()),
-                           JS_COLLECTION_SUB_TYPE, 0);
+void ObjectStatsCollectorImpl::RecordVirtualJSFunctionDetails(
+    JSFunction* function) {
+  // Uncompiled JSFunctions get their own category.
+  if (!function->is_compiled()) {
+    RecordSimpleVirtualObjectStats(nullptr, function,
+                                   ObjectStats::UNCOMPILED_JS_FUNCTION_TYPE);
   }
 }
 
-void ObjectStatsCollectorImpl::RecordScriptDetails(Script* obj) {
-  FixedArray* infos = FixedArray::cast(obj->shared_function_infos());
-  RecordFixedArrayHelper(obj, infos, SHARED_FUNCTION_INFOS_SUB_TYPE, 0);
-}
+namespace {
 
-void ObjectStatsCollectorImpl::RecordMapDetails(Map* map_obj) {
-  DescriptorArray* array = map_obj->instance_descriptors();
-  if (map_obj->owns_descriptors() && array != heap_->empty_descriptor_array() &&
-      SameLiveness(map_obj, array)) {
-    RecordFixedArrayHelper(map_obj, array, DESCRIPTOR_ARRAY_SUB_TYPE, 0);
-    EnumCache* enum_cache = array->GetEnumCache();
-    RecordFixedArrayHelper(array, enum_cache->keys(), ENUM_CACHE_SUB_TYPE, 0);
-    RecordFixedArrayHelper(array, enum_cache->indices(),
-                           ENUM_INDICES_CACHE_SUB_TYPE, 0);
-  }
+bool MatchesConstantElementsPair(Object* object) {
+  if (!object->IsTuple2()) return false;
+  Tuple2* tuple = Tuple2::cast(object);
+  return tuple->value1()->IsSmi() && tuple->value2()->IsFixedArray();
+}
 
-  for (DependentCode* cur_dependent_code = map_obj->dependent_code();
-       cur_dependent_code != heap_->empty_fixed_array();
-       cur_dependent_code = DependentCode::cast(
-           cur_dependent_code->get(DependentCode::kNextLinkIndex))) {
-    RecordFixedArrayHelper(map_obj, cur_dependent_code, DEPENDENT_CODE_SUB_TYPE,
-                           0);
-  }
+}  // namespace
 
-  if (map_obj->is_prototype_map()) {
-    if (map_obj->prototype_info()->IsPrototypeInfo()) {
-      PrototypeInfo* info = PrototypeInfo::cast(map_obj->prototype_info());
-      Object* users = info->prototype_users();
-      if (users->IsWeakFixedArray()) {
-        RecordFixedArrayHelper(map_obj, WeakFixedArray::cast(users),
-                               PROTOTYPE_USERS_SUB_TYPE, 0);
+void ObjectStatsCollectorImpl::
+    RecordVirtualObjectsForConstantPoolOrEmbeddedObjects(
+        HeapObject* parent, HeapObject* object,
+        ObjectStats::VirtualInstanceType type) {
+  if (RecordSimpleVirtualObjectStats(parent, object, type)) {
+    if (object->IsFixedArray()) {
+      FixedArray* array = FixedArray::cast(object);
+      for (int i = 0; i < array->length(); i++) {
+        Object* entry = array->get(i);
+        if (!entry->IsHeapObject()) continue;
+        RecordVirtualObjectsForConstantPoolOrEmbeddedObjects(
+            array, HeapObject::cast(entry), type);
       }
+    } else if (MatchesConstantElementsPair(object)) {
+      Tuple2* tuple = Tuple2::cast(object);
+      RecordVirtualObjectsForConstantPoolOrEmbeddedObjects(
+          tuple, HeapObject::cast(tuple->value2()), type);
     }
   }
 }
 
-void ObjectStatsCollectorImpl::RecordTemplateInfoDetails(TemplateInfo* obj) {
-  if (obj->property_accessors()->IsFixedArray()) {
-    RecordFixedArrayHelper(obj, FixedArray::cast(obj->property_accessors()),
-                           TEMPLATE_INFO_SUB_TYPE, 0);
-  }
-  if (obj->property_list()->IsFixedArray()) {
-    RecordFixedArrayHelper(obj, FixedArray::cast(obj->property_list()),
-                           TEMPLATE_INFO_SUB_TYPE, 0);
+void ObjectStatsCollectorImpl::RecordVirtualBytecodeArrayDetails(
+    BytecodeArray* bytecode) {
+  RecordSimpleVirtualObjectStats(
+      bytecode, bytecode->constant_pool(),
+      ObjectStats::BYTECODE_ARRAY_CONSTANT_POOL_TYPE);
+  // FixedArrays on constant pool are used for holding descriptor information.
+  // They are shared with optimized code.
+  FixedArray* constant_pool = FixedArray::cast(bytecode->constant_pool());
+  for (int i = 0; i < constant_pool->length(); i++) {
+    Object* entry = constant_pool->get(i);
+    if (entry->IsFixedArray() || MatchesConstantElementsPair(entry)) {
+      RecordVirtualObjectsForConstantPoolOrEmbeddedObjects(
+          constant_pool, HeapObject::cast(entry),
+          ObjectStats::EMBEDDED_OBJECT_TYPE);
+    }
   }
+  RecordSimpleVirtualObjectStats(
+      bytecode, bytecode->handler_table(),
+      ObjectStats::BYTECODE_ARRAY_HANDLER_TABLE_TYPE);
 }
 
-void ObjectStatsCollectorImpl::RecordBytecodeArrayDetails(BytecodeArray* obj) {
-  RecordFixedArrayHelper(obj, obj->constant_pool(),
-                         BYTECODE_ARRAY_CONSTANT_POOL_SUB_TYPE, 0);
-  RecordFixedArrayHelper(obj, obj->handler_table(),
-                         BYTECODE_ARRAY_HANDLER_TABLE_SUB_TYPE, 0);
+namespace {
+
+ObjectStats::VirtualInstanceType CodeKindToVirtualInstanceType(
+    Code::Kind kind) {
+  switch (kind) {
+#define CODE_KIND_CASE(type) \
+  case Code::type:           \
+    return ObjectStats::type;
+    CODE_KIND_LIST(CODE_KIND_CASE)
+#undef CODE_KIND_CASE
+    default:
+      UNREACHABLE();
+  }
+  UNREACHABLE();
 }
 
-void ObjectStatsCollectorImpl::RecordCodeDetails(Code* code) {
-  stats_->RecordCodeSubTypeStats(code->kind(), code->Size());
-  RecordFixedArrayHelper(code, code->deoptimization_data(),
-                         DEOPTIMIZATION_DATA_SUB_TYPE, 0);
+}  // namespace
+
+void ObjectStatsCollectorImpl::RecordVirtualCodeDetails(Code* code) {
+  RecordSimpleVirtualObjectStats(nullptr, code,
+                                 CodeKindToVirtualInstanceType(code->kind()));
+  RecordSimpleVirtualObjectStats(code, code->deoptimization_data(),
+                                 ObjectStats::DEOPTIMIZATION_DATA_TYPE);
   if (code->kind() == Code::Kind::OPTIMIZED_FUNCTION) {
     DeoptimizationData* input_data =
         DeoptimizationData::cast(code->deoptimization_data());
     if (input_data->length() > 0) {
-      RecordFixedArrayHelper(code->deoptimization_data(),
-                             input_data->LiteralArray(),
-                             OPTIMIZED_CODE_LITERALS_SUB_TYPE, 0);
+      RecordSimpleVirtualObjectStats(code->deoptimization_data(),
+                                     input_data->LiteralArray(),
+                                     ObjectStats::OPTIMIZED_CODE_LITERALS_TYPE);
     }
   }
-  RecordFixedArrayHelper(code, code->handler_table(), HANDLER_TABLE_SUB_TYPE,
-                         0);
   int const mode_mask = RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT);
   for (RelocIterator it(code, mode_mask); !it.done(); it.next()) {
     RelocInfo::Mode mode = it.rinfo()->rmode();
     if (mode == RelocInfo::EMBEDDED_OBJECT) {
       Object* target = it.rinfo()->target_object();
-      if (target->IsFixedArray()) {
-        RecursivelyRecordFixedArrayHelper(code, FixedArray::cast(target),
-                                          EMBEDDED_OBJECT_SUB_TYPE);
+      if (target->IsFixedArray() || MatchesConstantElementsPair(target)) {
+        RecordVirtualObjectsForConstantPoolOrEmbeddedObjects(
+            code, HeapObject::cast(target), ObjectStats::EMBEDDED_OBJECT_TYPE);
       }
     }
   }
 }
 
-void ObjectStatsCollectorImpl::RecordSharedFunctionInfoDetails(
-    SharedFunctionInfo* sfi) {
-  FixedArray* scope_info = sfi->scope_info();
-  RecordFixedArrayHelper(sfi, scope_info, SCOPE_INFO_SUB_TYPE, 0);
-  FeedbackMetadata* feedback_metadata = sfi->feedback_metadata();
-  if (!feedback_metadata->is_empty()) {
-    RecordFixedArrayHelper(sfi, feedback_metadata, FEEDBACK_METADATA_SUB_TYPE,
-                           0);
-  }
-}
-
-void ObjectStatsCollectorImpl::RecordFixedArrayDetails(FixedArray* array) {
-  if (array->IsContext()) {
-    RecordFixedArrayHelper(nullptr, array, CONTEXT_SUB_TYPE, 0);
-  }
-  if (IsCowArray(heap_, array) && CanRecordFixedArray(heap_, array)) {
-    stats_->RecordFixedArraySubTypeStats(array, COPY_ON_WRITE_SUB_TYPE,
-                                         array->Size(), 0);
-  }
-  if (array->IsNativeContext()) {
-    Context* native_ctx = Context::cast(array);
-    RecordHashTableHelper(array,
-                          native_ctx->slow_template_instantiations_cache(),
-                          SLOW_TEMPLATE_INSTANTIATIONS_CACHE_SUB_TYPE);
-    FixedArray* fast_cache = native_ctx->fast_template_instantiations_cache();
-    stats_->RecordFixedArraySubTypeStats(
-        fast_cache, FAST_TEMPLATE_INSTANTIATIONS_CACHE_SUB_TYPE,
-        fast_cache->Size(), 0);
+void ObjectStatsCollectorImpl::RecordVirtualContext(Context* context) {
+  if (context->IsNativeContext()) {
+    RecordSimpleVirtualObjectStats(nullptr, context,
+                                   ObjectStats::NATIVE_CONTEXT_TYPE);
+  } else if (context->IsFunctionContext()) {
+    RecordSimpleVirtualObjectStats(nullptr, context,
+                                   ObjectStats::FUNCTION_CONTEXT_TYPE);
+  } else {
+    RecordSimpleVirtualObjectStats(nullptr, context,
+                                   ObjectStats::OTHER_CONTEXT_TYPE);
   }
 }
 
 class ObjectStatsVisitor {
  public:
-  enum CollectionMode {
-    kRegular,
-    kVirtual,
-  };
-
   ObjectStatsVisitor(Heap* heap, ObjectStatsCollectorImpl* live_collector,
                      ObjectStatsCollectorImpl* dead_collector,
-                     CollectionMode mode)
+                     ObjectStatsCollectorImpl::Phase phase)
       : live_collector_(live_collector),
         dead_collector_(dead_collector),
         marking_state_(
             heap->mark_compact_collector()->non_atomic_marking_state()),
-        mode_(mode) {}
+        phase_(phase) {}
 
   bool Visit(HeapObject* obj, int size) {
     if (marking_state_->IsBlack(obj)) {
-      Collect(live_collector_, obj);
+      live_collector_->CollectStatistics(obj, phase_);
     } else {
       DCHECK(!marking_state_->IsGrey(obj));
-      Collect(dead_collector_, obj);
+      dead_collector_->CollectStatistics(obj, phase_);
     }
     return true;
   }
 
  private:
-  void Collect(ObjectStatsCollectorImpl* collector, HeapObject* obj) {
-    switch (mode_) {
-      case kRegular:
-        collector->CollectStatistics(obj);
-        break;
-      case kVirtual:
-        collector->CollectVirtualStatistics(obj);
-        break;
-    }
-  }
-
   ObjectStatsCollectorImpl* live_collector_;
   ObjectStatsCollectorImpl* dead_collector_;
   MarkCompactCollector::NonAtomicMarkingState* marking_state_;
-  CollectionMode mode_;
+  ObjectStatsCollectorImpl::Phase phase_;
 };
 
 namespace {
@@ -731,19 +854,10 @@ void IterateHeap(Heap* heap, ObjectStatsVisitor* visitor) {
 void ObjectStatsCollector::Collect() {
   ObjectStatsCollectorImpl live_collector(heap_, live_);
   ObjectStatsCollectorImpl dead_collector(heap_, dead_);
-  // 1. Collect system type otherwise indistinguishable from other types.
-  {
-    ObjectStatsVisitor visitor(heap_, &live_collector, &dead_collector,
-                               ObjectStatsVisitor::kVirtual);
-    IterateHeap(heap_, &visitor);
-  }
-
-  // 2. Collect globals; only applies to live objects.
   live_collector.CollectGlobalStatistics();
-  // 3. Collect rest.
-  {
+  for (int i = 0; i < ObjectStatsCollectorImpl::kNumberOfPhases; i++) {
     ObjectStatsVisitor visitor(heap_, &live_collector, &dead_collector,
-                               ObjectStatsVisitor::kRegular);
+                               static_cast<ObjectStatsCollectorImpl::Phase>(i));
     IterateHeap(heap_, &visitor);
   }
 }
diff --git a/deps/v8/src/heap/object-stats.h b/deps/v8/src/heap/object-stats.h
index 500ce36bd9..723ae53fd5 100644
--- a/deps/v8/src/heap/object-stats.h
+++ b/deps/v8/src/heap/object-stats.h
@@ -5,13 +5,8 @@
 #ifndef V8_HEAP_OBJECT_STATS_H_
 #define V8_HEAP_OBJECT_STATS_H_
 
-#include <set>
-
-#include "src/base/ieee754.h"
-#include "src/heap/heap.h"
-#include "src/heap/mark-compact.h"
-#include "src/heap/objects-visiting.h"
 #include "src/objects.h"
+#include "src/objects/code.h"
 
 // These instance types do not exist for actual use but are merely introduced
 // for object stats tracing. In contrast to Code and FixedArray sub types
@@ -19,18 +14,71 @@
 // tracing.
 //
 // Update LAST_VIRTUAL_TYPE below when changing this macro.
-#define VIRTUAL_INSTANCE_TYPE_LIST(V) \
-  V(BOILERPLATE_ELEMENTS_TYPE)        \
-  V(BOILERPLATE_NAME_DICTIONARY_TYPE) \
-  V(BOILERPLATE_PROPERTY_ARRAY_TYPE)  \
-  V(JS_ARRAY_BOILERPLATE_TYPE)        \
-  V(JS_OBJECT_BOILERPLATE_TYPE)
+#define VIRTUAL_INSTANCE_TYPE_LIST(V)       \
+  CODE_KIND_LIST(V)                         \
+  V(BOILERPLATE_ELEMENTS_TYPE)              \
+  V(BOILERPLATE_PROPERTY_ARRAY_TYPE)        \
+  V(BOILERPLATE_PROPERTY_DICTIONARY_TYPE)   \
+  V(BYTECODE_ARRAY_CONSTANT_POOL_TYPE)      \
+  V(BYTECODE_ARRAY_HANDLER_TABLE_TYPE)      \
+  V(CODE_STUBS_TABLE_TYPE)                  \
+  V(COW_ARRAY_TYPE)                         \
+  V(DEOPTIMIZATION_DATA_TYPE)               \
+  V(DEPENDENT_CODE_TYPE)                    \
+  V(ELEMENTS_TYPE)                          \
+  V(EMBEDDED_OBJECT_TYPE)                   \
+  V(ENUM_CACHE_TYPE)                        \
+  V(ENUM_INDICES_CACHE_TYPE)                \
+  V(FEEDBACK_METADATA_TYPE)                 \
+  V(FEEDBACK_VECTOR_ENTRY_TYPE)             \
+  V(FEEDBACK_VECTOR_HEADER_TYPE)            \
+  V(FEEDBACK_VECTOR_SLOT_CALL_TYPE)         \
+  V(FEEDBACK_VECTOR_SLOT_CALL_UNUSED_TYPE)  \
+  V(FEEDBACK_VECTOR_SLOT_ENUM_TYPE)         \
+  V(FEEDBACK_VECTOR_SLOT_LOAD_TYPE)         \
+  V(FEEDBACK_VECTOR_SLOT_LOAD_UNUSED_TYPE)  \
+  V(FEEDBACK_VECTOR_SLOT_OTHER_TYPE)        \
+  V(FEEDBACK_VECTOR_SLOT_STORE_TYPE)        \
+  V(FEEDBACK_VECTOR_SLOT_STORE_UNUSED_TYPE) \
+  V(FUNCTION_CONTEXT_TYPE)                  \
+  V(FUNCTION_TEMPLATE_INFO_ENTRIES_TYPE)    \
+  V(GLOBAL_ELEMENTS_TYPE)                   \
+  V(GLOBAL_PROPERTIES_TYPE)                 \
+  V(JS_ARRAY_BOILERPLATE_TYPE)              \
+  V(JS_COLLETION_TABLE_TYPE)                \
+  V(JS_OBJECT_BOILERPLATE_TYPE)             \
+  V(NATIVE_CONTEXT_TYPE)                    \
+  V(NOSCRIPT_SHARED_FUNCTION_INFOS_TYPE)    \
+  V(NUMBER_STRING_CACHE_TYPE)               \
+  V(OBJECT_PROPERTY_DICTIONARY_TYPE)        \
+  V(OBJECT_TO_CODE_TYPE)                    \
+  V(OPTIMIZED_CODE_LITERALS_TYPE)           \
+  V(OTHER_CONTEXT_TYPE)                     \
+  V(PROTOTYPE_USERS_TYPE)                   \
+  V(REGEXP_MULTIPLE_CACHE_TYPE)             \
+  V(RETAINED_MAPS_TYPE)                     \
+  V(SCRIPT_LIST_TYPE)                       \
+  V(SCRIPT_SHARED_FUNCTION_INFOS_TYPE)      \
+  V(SCRIPT_SOURCE_EXTERNAL_TYPE)            \
+  V(SCRIPT_SOURCE_NON_EXTERNAL_TYPE)        \
+  V(SERIALIZED_OBJECTS_TYPE)                \
+  V(SINGLE_CHARACTER_STRING_CACHE_TYPE)     \
+  V(STRING_SPLIT_CACHE_TYPE)                \
+  V(STRING_TABLE_TYPE)                      \
+  V(UNCOMPILED_JS_FUNCTION_TYPE)            \
+  V(UNCOMPILED_SHARED_FUNCTION_INFO_TYPE)   \
+  V(WEAK_NEW_SPACE_OBJECT_TO_CODE_TYPE)
 
 namespace v8 {
 namespace internal {
 
+class Heap;
+class Isolate;
+
 class ObjectStats {
  public:
+  static const size_t kNoOverAllocation = 0;
+
   explicit ObjectStats(Heap* heap) : heap_(heap) { ClearObjectStats(); }
 
   // See description on VIRTUAL_INSTANCE_TYPE_LIST.
@@ -38,18 +86,14 @@ class ObjectStats {
 #define DEFINE_VIRTUAL_INSTANCE_TYPE(type) type,
     VIRTUAL_INSTANCE_TYPE_LIST(DEFINE_VIRTUAL_INSTANCE_TYPE)
 #undef DEFINE_FIXED_ARRAY_SUB_INSTANCE_TYPE
-        LAST_VIRTUAL_TYPE = JS_OBJECT_BOILERPLATE_TYPE,
+        LAST_VIRTUAL_TYPE = WEAK_NEW_SPACE_OBJECT_TO_CODE_TYPE,
   };
 
   // ObjectStats are kept in two arrays, counts and sizes. Related stats are
   // stored in a contiguous linear buffer. Stats groups are stored one after
   // another.
   enum {
-    FIRST_CODE_KIND_SUB_TYPE = LAST_TYPE + 1,
-    FIRST_FIXED_ARRAY_SUB_TYPE =
-        FIRST_CODE_KIND_SUB_TYPE + Code::NUMBER_OF_KINDS,
-    FIRST_VIRTUAL_TYPE =
-        FIRST_FIXED_ARRAY_SUB_TYPE + LAST_FIXED_ARRAY_SUB_TYPE + 1,
+    FIRST_VIRTUAL_TYPE = LAST_TYPE + 1,
     OBJECT_STATS_COUNT = FIRST_VIRTUAL_TYPE + LAST_VIRTUAL_TYPE + 1,
   };
 
@@ -60,10 +104,8 @@ class ObjectStats {
 
   void CheckpointObjectStats();
   void RecordObjectStats(InstanceType type, size_t size);
-  void RecordVirtualObjectStats(VirtualInstanceType type, size_t size);
-  void RecordCodeSubTypeStats(int code_sub_type, size_t size);
-  bool RecordFixedArraySubTypeStats(FixedArrayBase* array, int array_sub_type,
-                                    size_t size, size_t over_allocated);
+  void RecordVirtualObjectStats(VirtualInstanceType type, size_t size,
+                                size_t over_allocated);
 
   size_t object_count_last_gc(size_t index) {
     return object_counts_last_time_[index];
@@ -105,8 +147,6 @@ class ObjectStats {
   // Detailed histograms by InstanceType.
   size_t size_histogram_[OBJECT_STATS_COUNT][kNumberOfBuckets];
   size_t over_allocated_histogram_[OBJECT_STATS_COUNT][kNumberOfBuckets];
-
-  std::set<FixedArrayBase*> visited_fixed_array_sub_types_;
 };
 
 class ObjectStatsCollector {
diff --git a/deps/v8/src/heap/objects-visiting-inl.h b/deps/v8/src/heap/objects-visiting-inl.h
index 0a8c866979..8384cead02 100644
--- a/deps/v8/src/heap/objects-visiting-inl.h
+++ b/deps/v8/src/heap/objects-visiting-inl.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_OBJECTS_VISITING_INL_H_
-#define V8_OBJECTS_VISITING_INL_H_
+#ifndef V8_HEAP_OBJECTS_VISITING_INL_H_
+#define V8_HEAP_OBJECTS_VISITING_INL_H_
 
 #include "src/heap/objects-visiting.h"
 
@@ -189,4 +189,4 @@ int NewSpaceVisitor<ConcreteVisitor>::VisitJSApiObject(Map* map,
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_OBJECTS_VISITING_INL_H_
+#endif  // V8_HEAP_OBJECTS_VISITING_INL_H_
diff --git a/deps/v8/src/heap/objects-visiting.h b/deps/v8/src/heap/objects-visiting.h
index c20434a283..7746c91c71 100644
--- a/deps/v8/src/heap/objects-visiting.h
+++ b/deps/v8/src/heap/objects-visiting.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_OBJECTS_VISITING_H_
-#define V8_OBJECTS_VISITING_H_
+#ifndef V8_HEAP_OBJECTS_VISITING_H_
+#define V8_HEAP_OBJECTS_VISITING_H_
 
 #include "src/allocation.h"
 #include "src/layout-descriptor.h"
@@ -31,6 +31,7 @@ class JSWeakCollection;
   V(Code)                        \
   V(CodeDataContainer)           \
   V(ConsString)                  \
+  V(FeedbackCell)                \
   V(FeedbackVector)              \
   V(FixedArray)                  \
   V(FixedDoubleArray)            \
@@ -132,4 +133,4 @@ Object* VisitWeakList(Heap* heap, Object* list, WeakObjectRetainer* retainer);
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_OBJECTS_VISITING_H_
+#endif  // V8_HEAP_OBJECTS_VISITING_H_
diff --git a/deps/v8/src/heap/remembered-set.h b/deps/v8/src/heap/remembered-set.h
index cd9c45141d..4e0f259c00 100644
--- a/deps/v8/src/heap/remembered-set.h
+++ b/deps/v8/src/heap/remembered-set.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_REMEMBERED_SET_H
-#define V8_REMEMBERED_SET_H
+#ifndef V8_HEAP_REMEMBERED_SET_H_
+#define V8_HEAP_REMEMBERED_SET_H_
 
 #include "src/assembler.h"
 #include "src/heap/heap.h"
@@ -298,8 +298,7 @@ class UpdateTypedSlotHelper {
     Object* new_target = old_target;
     SlotCallbackResult result = callback(&new_target);
     if (new_target != old_target) {
-      rinfo->set_target_address(old_target->GetIsolate(),
-                                Code::cast(new_target)->instruction_start());
+      rinfo->set_target_address(Code::cast(new_target)->instruction_start());
     }
     return result;
   }
@@ -359,4 +358,4 @@ inline SlotType SlotTypeForRelocInfoMode(RelocInfo::Mode rmode) {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_REMEMBERED_SET_H
+#endif  // V8_HEAP_REMEMBERED_SET_H_
diff --git a/deps/v8/src/heap/scavenge-job.h b/deps/v8/src/heap/scavenge-job.h
index e84659c6d4..34f7bfafc3 100644
--- a/deps/v8/src/heap/scavenge-job.h
+++ b/deps/v8/src/heap/scavenge-job.h
@@ -64,7 +64,7 @@ class V8_EXPORT_PRIVATE ScavengeJob {
   static const int kAverageIdleTimeMs = 5;
   // The number of bytes to be allocated in new space before the next idle
   // task is posted.
-  static const size_t kBytesAllocatedBeforeNextIdleTask = 512 * KB;
+  static const size_t kBytesAllocatedBeforeNextIdleTask = 1024 * KB;
   // The minimum size of allocated new space objects to trigger a scavenge.
   static const size_t kMinAllocationLimit = 512 * KB;
   // The allocation limit cannot exceed this fraction of the new space capacity.
diff --git a/deps/v8/src/heap/scavenger-inl.h b/deps/v8/src/heap/scavenger-inl.h
index b61872074e..2971db98cc 100644
--- a/deps/v8/src/heap/scavenger-inl.h
+++ b/deps/v8/src/heap/scavenger-inl.h
@@ -71,7 +71,7 @@ bool Scavenger::MigrateObject(Map* map, HeapObject* source, HeapObject* target,
 bool Scavenger::SemiSpaceCopyObject(Map* map, HeapObject** slot,
                                     HeapObject* object, int object_size) {
   DCHECK(heap()->AllowedToBeMigrated(object, NEW_SPACE));
-  AllocationAlignment alignment = object->RequiredAlignment();
+  AllocationAlignment alignment = HeapObject::RequiredAlignment(map);
   AllocationResult allocation =
       allocator_.Allocate(NEW_SPACE, object_size, alignment);
 
@@ -97,7 +97,7 @@ bool Scavenger::SemiSpaceCopyObject(Map* map, HeapObject** slot,
 
 bool Scavenger::PromoteObject(Map* map, HeapObject** slot, HeapObject* object,
                               int object_size) {
-  AllocationAlignment alignment = object->RequiredAlignment();
+  AllocationAlignment alignment = HeapObject::RequiredAlignment(map);
   AllocationResult allocation =
       allocator_.Allocate(OLD_SPACE, object_size, alignment);
 
@@ -228,9 +228,8 @@ void Scavenger::ScavengeObject(HeapObject** p, HeapObject* object) {
   // If the first word is a forwarding address, the object has already been
   // copied.
   if (first_word.IsForwardingAddress()) {
-    HeapObject* dest = first_word.ToForwardingAddress();
-    DCHECK(object->GetIsolate()->heap()->InFromSpace(*p));
-    base::AsAtomicPointer::Relaxed_Store(p, dest);
+    DCHECK(heap()->InFromSpace(*p));
+    *p = first_word.ToForwardingAddress();
     return;
   }
 
diff --git a/deps/v8/src/heap/scavenger.cc b/deps/v8/src/heap/scavenger.cc
index be5fb87a90..3baba9521b 100644
--- a/deps/v8/src/heap/scavenger.cc
+++ b/deps/v8/src/heap/scavenger.cc
@@ -97,6 +97,7 @@ void Scavenger::AddPageToSweeperIfNecessary(MemoryChunk* page) {
 }
 
 void Scavenger::ScavengePage(MemoryChunk* page) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"), "Scavenger::ScavengePage");
   CodePageMemoryModificationScope memory_modification_scope(page);
   RememberedSet<OLD_TO_NEW>::Iterate(
       page,
@@ -115,6 +116,7 @@ void Scavenger::ScavengePage(MemoryChunk* page) {
 }
 
 void Scavenger::Process(OneshotBarrier* barrier) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"), "Scavenger::Process");
   // Threshold when to switch processing the promotion list to avoid
   // allocating too much backing store in the worklist.
   const int kProcessPromotionListThreshold = kPromotionListSegmentSize / 2;
@@ -160,12 +162,13 @@ void Scavenger::Finalize() {
   allocator_.Finalize();
 }
 
-void RootScavengeVisitor::VisitRootPointer(Root root, Object** p) {
+void RootScavengeVisitor::VisitRootPointer(Root root, const char* description,
+                                           Object** p) {
   ScavengePointer(p);
 }
 
-void RootScavengeVisitor::VisitRootPointers(Root root, Object** start,
-                                            Object** end) {
+void RootScavengeVisitor::VisitRootPointers(Root root, const char* description,
+                                            Object** start, Object** end) {
   // Copy all HeapObject pointers in [start, end)
   for (Object** p = start; p < end; p++) ScavengePointer(p);
 }
diff --git a/deps/v8/src/heap/scavenger.h b/deps/v8/src/heap/scavenger.h
index 27ae2e8ab7..e0008ae694 100644
--- a/deps/v8/src/heap/scavenger.h
+++ b/deps/v8/src/heap/scavenger.h
@@ -117,8 +117,9 @@ class RootScavengeVisitor final : public RootVisitor {
   RootScavengeVisitor(Heap* heap, Scavenger* scavenger)
       : heap_(heap), scavenger_(scavenger) {}
 
-  void VisitRootPointer(Root root, Object** p) final;
-  void VisitRootPointers(Root root, Object** start, Object** end) final;
+  void VisitRootPointer(Root root, const char* description, Object** p) final;
+  void VisitRootPointers(Root root, const char* description, Object** start,
+                         Object** end) final;
 
  private:
   void ScavengePointer(Object** p);
diff --git a/deps/v8/src/heap/setup-heap-internal.cc b/deps/v8/src/heap/setup-heap-internal.cc
index 9e2d7e6354..8a7aca1694 100644
--- a/deps/v8/src/heap/setup-heap-internal.cc
+++ b/deps/v8/src/heap/setup-heap-internal.cc
@@ -222,7 +222,7 @@ bool Heap::CreateInitialMaps() {
           (constructor_function_index));                          \
     }
 
-    ALLOCATE_VARSIZE_MAP(FIXED_ARRAY_TYPE, scope_info)
+    ALLOCATE_VARSIZE_MAP(SCOPE_INFO_TYPE, scope_info)
     ALLOCATE_VARSIZE_MAP(FIXED_ARRAY_TYPE, module_info)
     ALLOCATE_VARSIZE_MAP(FEEDBACK_VECTOR_TYPE, feedback_vector)
     ALLOCATE_PRIMITIVE_MAP(HEAP_NUMBER_TYPE, HeapNumber::kSize, heap_number,
@@ -289,12 +289,17 @@ bool Heap::CreateInitialMaps() {
     ALLOCATE_MAP(CELL_TYPE, Cell::kSize, cell)
     ALLOCATE_MAP(PROPERTY_CELL_TYPE, PropertyCell::kSize, global_property_cell)
     ALLOCATE_MAP(WEAK_CELL_TYPE, WeakCell::kSize, weak_cell)
-    ALLOCATE_MAP(CELL_TYPE, Cell::kSize, no_closures_cell)
-    ALLOCATE_MAP(CELL_TYPE, Cell::kSize, one_closure_cell)
-    ALLOCATE_MAP(CELL_TYPE, Cell::kSize, many_closures_cell)
     ALLOCATE_MAP(FILLER_TYPE, kPointerSize, one_pointer_filler)
     ALLOCATE_MAP(FILLER_TYPE, 2 * kPointerSize, two_pointer_filler)
 
+    // The "no closures" and "one closure" FeedbackCell maps need
+    // to be marked unstable because their objects can change maps.
+    ALLOCATE_MAP(FEEDBACK_CELL_TYPE, FeedbackCell::kSize, no_closures_cell)
+    no_closures_cell_map()->mark_unstable();
+    ALLOCATE_MAP(FEEDBACK_CELL_TYPE, FeedbackCell::kSize, one_closure_cell)
+    one_closure_cell_map()->mark_unstable();
+    ALLOCATE_MAP(FEEDBACK_CELL_TYPE, FeedbackCell::kSize, many_closures_cell)
+
     ALLOCATE_VARSIZE_MAP(TRANSITION_ARRAY_TYPE, transition_array)
 
     ALLOCATE_VARSIZE_MAP(HASH_TABLE_TYPE, hash_table)
@@ -303,6 +308,7 @@ bool Heap::CreateInitialMaps() {
     ALLOCATE_VARSIZE_MAP(HASH_TABLE_TYPE, name_dictionary)
     ALLOCATE_VARSIZE_MAP(HASH_TABLE_TYPE, global_dictionary)
     ALLOCATE_VARSIZE_MAP(HASH_TABLE_TYPE, number_dictionary)
+    ALLOCATE_VARSIZE_MAP(HASH_TABLE_TYPE, simple_number_dictionary)
     ALLOCATE_VARSIZE_MAP(HASH_TABLE_TYPE, string_table)
     ALLOCATE_VARSIZE_MAP(HASH_TABLE_TYPE, weak_hash_table)
 
@@ -475,7 +481,7 @@ void Heap::CreateInitialObjects() {
 
   // Create the code_stubs dictionary. The initial size is set to avoid
   // expanding the dictionary during bootstrapping.
-  set_code_stubs(*NumberDictionary::New(isolate(), 128));
+  set_code_stubs(*SimpleNumberDictionary::New(isolate(), 128));
 
   {
     HandleScope scope(isolate());
@@ -533,7 +539,10 @@ void Heap::CreateInitialObjects() {
   set_regexp_multiple_cache(*factory->NewFixedArray(
       RegExpResultsCache::kRegExpResultsCacheSize, TENURED));
 
-  set_undefined_cell(*factory->NewCell(factory->undefined_value()));
+  // Allocate FeedbackCell for builtins.
+  Handle<FeedbackCell> many_closures_cell =
+      factory->NewManyClosuresCell(factory->undefined_value());
+  set_many_closures_cell(*many_closures_cell);
 
   // Microtask queue uses the empty fixed array as a sentinel for "empty".
   // Number of queued microtasks stored in Isolate::pending_microtask_count().
@@ -638,6 +647,14 @@ void Heap::CreateInitialObjects() {
   cell->set_value(Smi::FromInt(Isolate::kProtectorValid));
   set_array_buffer_neutering_protector(*cell);
 
+  cell = factory->NewPropertyCell(factory->empty_string());
+  cell->set_value(Smi::FromInt(Isolate::kProtectorValid));
+  set_promise_hook_protector(*cell);
+
+  cell = factory->NewPropertyCell(factory->empty_string());
+  cell->set_value(Smi::FromInt(Isolate::kProtectorValid));
+  set_promise_then_protector(*cell);
+
   set_serialized_objects(empty_fixed_array());
   set_serialized_global_proxy_sizes(empty_fixed_array());
 
@@ -650,6 +667,9 @@ void Heap::CreateInitialObjects() {
   set_deserialize_lazy_handler_wide(Smi::kZero);
   set_deserialize_lazy_handler_extra_wide(Smi::kZero);
 
+  // Initialize builtins constants table.
+  set_builtins_constants_table(empty_fixed_array());
+
   // Initialize context slot cache.
   isolate_->context_slot_cache()->Clear();
 
diff --git a/deps/v8/src/heap/slot-set.h b/deps/v8/src/heap/slot-set.h
index f1edb6f2fb..7423665bcb 100644
--- a/deps/v8/src/heap/slot-set.h
+++ b/deps/v8/src/heap/slot-set.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_SLOT_SET_H
-#define V8_SLOT_SET_H
+#ifndef V8_HEAP_SLOT_SET_H_
+#define V8_HEAP_SLOT_SET_H_
 
 #include <map>
 #include <stack>
@@ -641,4 +641,4 @@ class TypedSlotSet {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_SLOT_SET_H
+#endif  // V8_HEAP_SLOT_SET_H_
diff --git a/deps/v8/src/heap/spaces-inl.h b/deps/v8/src/heap/spaces-inl.h
index 39a62327df..498c34bd54 100644
--- a/deps/v8/src/heap/spaces-inl.h
+++ b/deps/v8/src/heap/spaces-inl.h
@@ -5,6 +5,7 @@
 #ifndef V8_HEAP_SPACES_INL_H_
 #define V8_HEAP_SPACES_INL_H_
 
+#include "src/base/v8-fallthrough.h"
 #include "src/heap/incremental-marking.h"
 #include "src/heap/spaces.h"
 #include "src/msan.h"
@@ -137,12 +138,6 @@ bool NewSpace::FromSpaceContainsSlow(Address a) {
 bool NewSpace::ToSpaceContains(Object* o) { return to_space_.Contains(o); }
 bool NewSpace::FromSpaceContains(Object* o) { return from_space_.Contains(o); }
 
-void MemoryChunk::InitializeFreeListCategories() {
-  for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
-    categories_[i].Initialize(static_cast<FreeListCategoryType>(i));
-  }
-}
-
 bool PagedSpace::Contains(Address addr) {
   if (heap_->lo_space()->FindPage(addr)) return false;
   return MemoryChunk::FromAnyPointerAddress(heap(), addr)->owner() == this;
@@ -157,6 +152,7 @@ void PagedSpace::UnlinkFreeListCategories(Page* page) {
   DCHECK_EQ(this, page->owner());
   page->ForAllFreeListCategories([this](FreeListCategory* category) {
     DCHECK_EQ(free_list(), category->owner());
+    category->set_free_list(nullptr);
     free_list()->RemoveCategory(category);
   });
 }
@@ -164,7 +160,8 @@ void PagedSpace::UnlinkFreeListCategories(Page* page) {
 size_t PagedSpace::RelinkFreeListCategories(Page* page) {
   DCHECK_EQ(this, page->owner());
   size_t added = 0;
-  page->ForAllFreeListCategories([&added](FreeListCategory* category) {
+  page->ForAllFreeListCategories([this, &added](FreeListCategory* category) {
+    category->set_free_list(&free_list_);
     added += category->available();
     category->Relink();
   });
@@ -230,23 +227,23 @@ MemoryChunk* MemoryChunkIterator::next() {
     case kOldSpaceState: {
       if (old_iterator_ != heap_->old_space()->end()) return *(old_iterator_++);
       state_ = kMapState;
-      // Fall through.
+      V8_FALLTHROUGH;
     }
     case kMapState: {
       if (map_iterator_ != heap_->map_space()->end()) return *(map_iterator_++);
       state_ = kCodeState;
-      // Fall through.
+      V8_FALLTHROUGH;
     }
     case kCodeState: {
       if (code_iterator_ != heap_->code_space()->end())
         return *(code_iterator_++);
       state_ = kLargeObjectState;
-      // Fall through.
+      V8_FALLTHROUGH;
     }
     case kLargeObjectState: {
       if (lo_iterator_ != heap_->lo_space()->end()) return *(lo_iterator_++);
       state_ = kFinishedState;
-      // Fall through;
+      V8_FALLTHROUGH;
     }
     case kFinishedState:
       return nullptr;
@@ -256,23 +253,14 @@ MemoryChunk* MemoryChunkIterator::next() {
   UNREACHABLE();
 }
 
-Page* FreeListCategory::page() const {
-  return Page::FromAddress(
-      reinterpret_cast<Address>(const_cast<FreeListCategory*>(this)));
-}
-
 Page* FreeList::GetPageForCategoryType(FreeListCategoryType type) {
   return top(type) ? top(type)->page() : nullptr;
 }
 
-FreeList* FreeListCategory::owner() {
-  return reinterpret_cast<PagedSpace*>(
-             Page::FromAddress(reinterpret_cast<Address>(this))->owner())
-      ->free_list();
-}
+FreeList* FreeListCategory::owner() { return free_list_; }
 
 bool FreeListCategory::is_linked() {
-  return prev_ != nullptr || next_ != nullptr || owner()->top(type_) == this;
+  return prev_ != nullptr || next_ != nullptr;
 }
 
 AllocationResult LocalAllocationBuffer::AllocateRawAligned(
diff --git a/deps/v8/src/heap/spaces.cc b/deps/v8/src/heap/spaces.cc
index 2dd5e9b24d..d90cac90f2 100644
--- a/deps/v8/src/heap/spaces.cc
+++ b/deps/v8/src/heap/spaces.cc
@@ -71,6 +71,8 @@ bool HeapObjectIterator::AdvanceToNextPage() {
 
 PauseAllocationObserversScope::PauseAllocationObserversScope(Heap* heap)
     : heap_(heap) {
+  DCHECK_EQ(heap->gc_state(), Heap::NOT_IN_GC);
+
   for (SpaceIterator it(heap_); it.has_next();) {
     it.next()->PauseAllocationObservers();
   }
@@ -322,7 +324,12 @@ class MemoryAllocator::Unmapper::UnmapFreeMemoryTask : public CancelableTask {
     TRACE_BACKGROUND_GC(tracer_,
                         GCTracer::BackgroundScope::BACKGROUND_UNMAPPER);
     unmapper_->PerformFreeMemoryOnQueuedChunks<FreeMode::kUncommitPooled>();
+    unmapper_->active_unmapping_tasks_.Decrement(1);
     unmapper_->pending_unmapping_tasks_semaphore_.Signal();
+    if (FLAG_trace_unmapper) {
+      PrintIsolate(unmapper_->heap_->isolate(),
+                   "UnmapFreeMemoryTask Done: id=%" PRIu64 "\n", id());
+    }
   }
 
   Unmapper* const unmapper_;
@@ -332,13 +339,26 @@ class MemoryAllocator::Unmapper::UnmapFreeMemoryTask : public CancelableTask {
 
 void MemoryAllocator::Unmapper::FreeQueuedChunks() {
   if (heap_->use_tasks() && FLAG_concurrent_sweeping) {
-    if (concurrent_unmapping_tasks_active_ >= kMaxUnmapperTasks) {
+    if (!MakeRoomForNewTasks()) {
       // kMaxUnmapperTasks are already running. Avoid creating any more.
+      if (FLAG_trace_unmapper) {
+        PrintIsolate(heap_->isolate(),
+                     "Unmapper::FreeQueuedChunks: reached task limit (%d)\n",
+                     kMaxUnmapperTasks);
+      }
       return;
     }
     UnmapFreeMemoryTask* task = new UnmapFreeMemoryTask(heap_->isolate(), this);
-    DCHECK_LT(concurrent_unmapping_tasks_active_, kMaxUnmapperTasks);
-    task_ids_[concurrent_unmapping_tasks_active_++] = task->id();
+    if (FLAG_trace_unmapper) {
+      PrintIsolate(heap_->isolate(),
+                   "Unmapper::FreeQueuedChunks: new task id=%" PRIu64 "\n",
+                   task->id());
+    }
+    DCHECK_LT(pending_unmapping_tasks_, kMaxUnmapperTasks);
+    DCHECK_LE(active_unmapping_tasks_.Value(), pending_unmapping_tasks_);
+    DCHECK_GE(active_unmapping_tasks_.Value(), 0);
+    active_unmapping_tasks_.Increment(1);
+    task_ids_[pending_unmapping_tasks_++] = task->id();
     V8::GetCurrentPlatform()->CallOnBackgroundThread(
         task, v8::Platform::kShortRunningTask);
   } else {
@@ -347,18 +367,41 @@ void MemoryAllocator::Unmapper::FreeQueuedChunks() {
 }
 
 void MemoryAllocator::Unmapper::WaitUntilCompleted() {
-  for (int i = 0; i < concurrent_unmapping_tasks_active_; i++) {
+  for (int i = 0; i < pending_unmapping_tasks_; i++) {
     if (heap_->isolate()->cancelable_task_manager()->TryAbort(task_ids_[i]) !=
         CancelableTaskManager::kTaskAborted) {
       pending_unmapping_tasks_semaphore_.Wait();
     }
   }
-  concurrent_unmapping_tasks_active_ = 0;
+  pending_unmapping_tasks_ = 0;
+  active_unmapping_tasks_.SetValue(0);
+
+  if (FLAG_trace_unmapper) {
+    PrintIsolate(heap_->isolate(),
+                 "Unmapper::WaitUntilCompleted: no tasks remaining\n");
+  }
+}
+
+bool MemoryAllocator::Unmapper::MakeRoomForNewTasks() {
+  DCHECK_LE(pending_unmapping_tasks_, kMaxUnmapperTasks);
+
+  if (active_unmapping_tasks_.Value() == 0 && pending_unmapping_tasks_ > 0) {
+    // All previous unmapping tasks have been run to completion.
+    // Finalize those tasks to make room for new ones.
+    WaitUntilCompleted();
+  }
+  return pending_unmapping_tasks_ != kMaxUnmapperTasks;
 }
 
 template <MemoryAllocator::Unmapper::FreeMode mode>
 void MemoryAllocator::Unmapper::PerformFreeMemoryOnQueuedChunks() {
   MemoryChunk* chunk = nullptr;
+  if (FLAG_trace_unmapper) {
+    PrintIsolate(
+        heap_->isolate(),
+        "Unmapper::PerformFreeMemoryOnQueuedChunks: %d queued chunks\n",
+        NumberOfChunks());
+  }
   // Regular chunks.
   while ((chunk = GetMemoryChunkSafe<kRegular>()) != nullptr) {
     bool pooled = chunk->IsFlagSet(MemoryChunk::POOLED);
@@ -380,7 +423,7 @@ void MemoryAllocator::Unmapper::PerformFreeMemoryOnQueuedChunks() {
 }
 
 void MemoryAllocator::Unmapper::TearDown() {
-  CHECK_EQ(0, concurrent_unmapping_tasks_active_);
+  CHECK_EQ(0, pending_unmapping_tasks_);
   PerformFreeMemoryOnQueuedChunks<FreeMode::kReleasePooled>();
   for (int i = 0; i < kNumberOfChunkQueues; i++) {
     DCHECK(chunks_[i].empty());
@@ -583,7 +626,10 @@ MemoryChunk* MemoryChunk::Initialize(Heap* heap, Address base, size_t size,
   chunk->set_next_chunk(nullptr);
   chunk->set_prev_chunk(nullptr);
   chunk->local_tracker_ = nullptr;
-  chunk->InitializeFreeListCategories();
+
+  for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
+    chunk->categories_[i] = nullptr;
+  }
 
   heap->incremental_marking()->non_atomic_marking_state()->ClearLiveness(chunk);
 
@@ -606,6 +652,7 @@ MemoryChunk* MemoryChunk::Initialize(Heap* heap, Address base, size_t size,
   if (reservation != nullptr) {
     chunk->reservation_.TakeControl(reservation);
   }
+
   return chunk;
 }
 
@@ -615,6 +662,8 @@ Page* PagedSpace::InitializePage(MemoryChunk* chunk, Executability executable) {
   // Make sure that categories are initialized before freeing the area.
   page->ResetAllocatedBytes();
   heap()->incremental_marking()->SetOldSpacePageFlags(page);
+  page->AllocateFreeListCategories();
+  page->InitializeFreeListCategories();
   page->InitializationMemoryFence();
   return page;
 }
@@ -662,6 +711,28 @@ LargePage* LargePage::Initialize(Heap* heap, MemoryChunk* chunk,
   return page;
 }
 
+void Page::AllocateFreeListCategories() {
+  for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
+    categories_[i] = new FreeListCategory(
+        reinterpret_cast<PagedSpace*>(owner())->free_list(), this);
+  }
+}
+
+void Page::InitializeFreeListCategories() {
+  for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
+    categories_[i]->Initialize(static_cast<FreeListCategoryType>(i));
+  }
+}
+
+void Page::ReleaseFreeListCategories() {
+  for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
+    if (categories_[i] != nullptr) {
+      delete categories_[i];
+      categories_[i] = nullptr;
+    }
+  }
+}
+
 Page* Page::ConvertNewToOld(Page* old_page) {
   DCHECK(!old_page->is_anchor());
   DCHECK(old_page->InNewSpace());
@@ -679,6 +750,10 @@ size_t MemoryChunk::CommittedPhysicalMemory() {
   return high_water_mark_.Value();
 }
 
+bool MemoryChunk::IsPagedSpace() const {
+  return owner()->identity() != LO_SPACE;
+}
+
 void MemoryChunk::InsertAfter(MemoryChunk* other) {
   MemoryChunk* other_next = other->next_chunk();
 
@@ -710,7 +785,8 @@ MemoryChunk* MemoryAllocator::AllocateChunk(size_t reserve_area_size,
   VirtualMemory reservation;
   Address area_start = nullptr;
   Address area_end = nullptr;
-  void* address_hint = heap->GetRandomMmapAddr();
+  void* address_hint =
+      AlignedAddress(heap->GetRandomMmapAddr(), MemoryChunk::kAlignment);
 
   //
   // MemoryChunk layout:
@@ -826,8 +902,12 @@ MemoryChunk* MemoryAllocator::AllocateChunk(size_t reserve_area_size,
                          owner);
   }
 
-  return MemoryChunk::Initialize(heap, base, chunk_size, area_start, area_end,
-                                 executable, owner, &reservation);
+  MemoryChunk* chunk =
+      MemoryChunk::Initialize(heap, base, chunk_size, area_start, area_end,
+                              executable, owner, &reservation);
+
+  if (chunk->executable()) RegisterExecutableMemoryChunk(chunk);
+  return chunk;
 }
 
 void Page::ResetAllocatedBytes() { allocated_bytes_ = area_size(); }
@@ -970,6 +1050,8 @@ void MemoryAllocator::PreFreeMemory(MemoryChunk* chunk) {
   }
 
   chunk->SetFlag(MemoryChunk::PRE_FREED);
+
+  if (chunk->executable()) UnregisterExecutableMemoryChunk(chunk);
 }
 
 
@@ -1005,7 +1087,7 @@ void MemoryAllocator::Free(MemoryChunk* chunk) {
       DCHECK_EQ(chunk->size(), static_cast<size_t>(MemoryChunk::kPageSize));
       DCHECK_EQ(chunk->executable(), NOT_EXECUTABLE);
       chunk->SetFlag(MemoryChunk::POOLED);
-    // Fall through to kPreFreeAndQueue.
+      V8_FALLTHROUGH;
     case kPreFreeAndQueue:
       PreFreeMemory(chunk);
       // The chunks added to this queue will be freed by a concurrent thread.
@@ -1198,6 +1280,11 @@ void MemoryChunk::ReleaseAllocatedMemory() {
   ReleaseInvalidatedSlots();
   if (local_tracker_ != nullptr) ReleaseLocalTracker();
   if (young_generation_bitmap_ != nullptr) ReleaseYoungGenerationBitmap();
+
+  if (IsPagedSpace()) {
+    Page* page = static_cast<Page*>(this);
+    page->ReleaseFreeListCategories();
+  }
 }
 
 static SlotSet* AllocateAndInitializeSlotSet(size_t size, Address page_start) {
@@ -1345,12 +1432,17 @@ void Space::ResumeAllocationObservers() {
 
 void Space::AllocationStep(int bytes_since_last, Address soon_object,
                            int size) {
-  if (AllocationObserversActive()) {
-    heap()->CreateFillerObjectAt(soon_object, size, ClearRecordedSlots::kNo);
-    for (AllocationObserver* observer : allocation_observers_) {
-      observer->AllocationStep(bytes_since_last, soon_object, size);
-    }
+  if (!AllocationObserversActive()) {
+    return;
+  }
+
+  DCHECK(!heap()->allocation_step_in_progress());
+  heap()->set_allocation_step_in_progress(true);
+  heap()->CreateFillerObjectAt(soon_object, size, ClearRecordedSlots::kNo);
+  for (AllocationObserver* observer : allocation_observers_) {
+    observer->AllocationStep(bytes_since_last, soon_object, size);
   }
+  heap()->set_allocation_step_in_progress(false);
 }
 
 intptr_t Space::GetNextInlineAllocationStepSize() {
@@ -1359,15 +1451,13 @@ intptr_t Space::GetNextInlineAllocationStepSize() {
     next_step = next_step ? Min(next_step, observer->bytes_to_next_step())
                           : observer->bytes_to_next_step();
   }
-  DCHECK(allocation_observers_.size() == 0 || next_step != 0);
+  DCHECK(allocation_observers_.size() == 0 || next_step > 0);
   return next_step;
 }
 
 PagedSpace::PagedSpace(Heap* heap, AllocationSpace space,
                        Executability executable)
-    : SpaceWithLinearArea(heap, space, executable),
-      anchor_(this),
-      free_list_(this) {
+    : SpaceWithLinearArea(heap, space, executable), anchor_(this) {
   area_size_ = MemoryAllocator::PageAreaSize(space);
   accounting_stats_.Clear();
 }
@@ -1570,7 +1660,8 @@ bool PagedSpace::Expand() {
   // Pages created during bootstrapping may contain immortal immovable objects.
   if (!heap()->deserialization_complete()) page->MarkNeverEvacuate();
   AddPage(page);
-  Free(page->area_start(), page->area_size());
+  Free(page->area_start(), page->area_size(),
+       SpaceAccountingMode::kSpaceAccounted);
   DCHECK(Capacity() <= heap()->MaxOldGenerationSize());
   return true;
 }
@@ -1606,7 +1697,8 @@ void PagedSpace::DecreaseLimit(Address new_limit) {
   DCHECK_GE(old_limit, new_limit);
   if (new_limit != old_limit) {
     SetTopAndLimit(top(), new_limit);
-    Free(new_limit, old_limit - new_limit);
+    Free(new_limit, old_limit - new_limit,
+         SpaceAccountingMode::kSpaceAccounted);
     if (heap()->incremental_marking()->black_allocation()) {
       Page::FromAllocationAreaAddress(new_limit)->DestroyBlackArea(new_limit,
                                                                    old_limit);
@@ -1692,7 +1784,8 @@ void PagedSpace::FreeLinearAllocationArea() {
   InlineAllocationStep(current_top, nullptr, nullptr, 0);
   SetTopAndLimit(nullptr, nullptr);
   DCHECK_GE(current_limit, current_top);
-  Free(current_top, current_limit - current_top);
+  Free(current_top, current_limit - current_top,
+       SpaceAccountingMode::kSpaceAccounted);
 }
 
 void PagedSpace::ReleasePage(Page* page) {
@@ -1722,6 +1815,7 @@ void PagedSpace::ReleasePage(Page* page) {
 void PagedSpace::SetReadAndExecutable() {
   DCHECK(identity() == CODE_SPACE);
   for (Page* page : *this) {
+    CHECK(heap_->memory_allocator()->IsMemoryChunkExecutable(page));
     page->SetReadAndExecutable();
   }
 }
@@ -1729,6 +1823,7 @@ void PagedSpace::SetReadAndExecutable() {
 void PagedSpace::SetReadAndWritable() {
   DCHECK(identity() == CODE_SPACE);
   for (Page* page : *this) {
+    CHECK(heap_->memory_allocator()->IsMemoryChunkExecutable(page));
     page->SetReadAndWritable();
   }
 }
@@ -1786,7 +1881,7 @@ bool PagedSpace::RefillLinearAllocationAreaFromFreeList(size_t size_in_bytes) {
   DCHECK_LE(limit, end);
   DCHECK_LE(size_in_bytes, limit - start);
   if (limit != end) {
-    Free(limit, end - limit);
+    Free(limit, end - limit, SpaceAccountingMode::kSpaceAccounted);
   }
   SetLinearAllocationArea(start, limit);
 
@@ -2078,22 +2173,21 @@ LocalAllocationBuffer& LocalAllocationBuffer::operator=(
 }
 
 void NewSpace::UpdateLinearAllocationArea() {
-  Address old_top = top();
-  Address new_top = to_space_.page_low();
+  // Make sure there is no unaccounted allocations.
+  DCHECK(!AllocationObserversActive() || top_on_previous_step_ == top());
 
+  Address new_top = to_space_.page_low();
   MemoryChunk::UpdateHighWaterMark(allocation_info_.top());
   allocation_info_.Reset(new_top, to_space_.page_high());
   original_top_.SetValue(top());
   original_limit_.SetValue(limit());
-  UpdateInlineAllocationLimit(0);
-  // TODO(ofrobots): It would be more correct to do a step before setting the
-  // limit on the new allocation area. However, fixing this causes a regression
-  // due to the idle scavenger getting pinged too frequently. crbug.com/795323.
-  InlineAllocationStep(old_top, new_top, nullptr, 0);
+  StartNextInlineAllocationStep();
   DCHECK_SEMISPACE_ALLOCATION_INFO(allocation_info_, to_space_);
 }
 
 void NewSpace::ResetLinearAllocationArea() {
+  // Do a step to account for memory allocated so far before resetting.
+  InlineAllocationStep(top(), top(), nullptr, 0);
   to_space_.Reset();
   UpdateLinearAllocationArea();
   // Clear all mark-bits in the to-space.
@@ -2121,6 +2215,10 @@ void PagedSpace::UpdateInlineAllocationLimit(size_t min_size) {
 bool NewSpace::AddFreshPage() {
   Address top = allocation_info_.top();
   DCHECK(!Page::IsAtObjectStart(top));
+
+  // Do a step to account for memory allocated on previous page.
+  InlineAllocationStep(top, top, nullptr, 0);
+
   if (!to_space_.AdvancePage()) {
     // No more pages left to advance.
     return false;
@@ -2176,6 +2274,11 @@ bool NewSpace::EnsureAllocation(int size_in_bytes,
 }
 
 void SpaceWithLinearArea::StartNextInlineAllocationStep() {
+  if (heap()->allocation_step_in_progress()) {
+    // If we are mid-way through an existing step, don't start a new one.
+    return;
+  }
+
   if (AllocationObserversActive()) {
     top_on_previous_step_ = top();
     UpdateInlineAllocationLimit(0);
@@ -2217,6 +2320,11 @@ void SpaceWithLinearArea::InlineAllocationStep(Address top,
                                                Address top_for_next_step,
                                                Address soon_object,
                                                size_t size) {
+  if (heap()->allocation_step_in_progress()) {
+    // Avoid starting a new step if we are mid-way through an existing one.
+    return;
+  }
+
   if (top_on_previous_step_) {
     if (top < top_on_previous_step_) {
       // Generated code decreased the top pointer to do folded allocations.
@@ -2608,7 +2716,6 @@ void FreeListCategory::Reset() {
 
 FreeSpace* FreeListCategory::PickNodeFromList(size_t* node_size) {
   DCHECK(page()->CanAllocate());
-
   FreeSpace* node = top();
   if (node == nullptr) return nullptr;
   set_top(node->next());
@@ -2620,10 +2727,9 @@ FreeSpace* FreeListCategory::PickNodeFromList(size_t* node_size) {
 FreeSpace* FreeListCategory::TryPickNodeFromList(size_t minimum_size,
                                                  size_t* node_size) {
   DCHECK(page()->CanAllocate());
-
   FreeSpace* node = PickNodeFromList(node_size);
   if ((node != nullptr) && (*node_size < minimum_size)) {
-    Free(node, *node_size, kLinkCategory);
+    Free(node->address(), *node_size, kLinkCategory);
     *node_size = 0;
     return nullptr;
   }
@@ -2633,7 +2739,6 @@ FreeSpace* FreeListCategory::TryPickNodeFromList(size_t minimum_size,
 FreeSpace* FreeListCategory::SearchForNodeInList(size_t minimum_size,
                                                  size_t* node_size) {
   DCHECK(page()->CanAllocate());
-
   FreeSpace* prev_non_evac_node = nullptr;
   for (FreeSpace* cur_node = top(); cur_node != nullptr;
        cur_node = cur_node->next()) {
@@ -2656,9 +2761,10 @@ FreeSpace* FreeListCategory::SearchForNodeInList(size_t minimum_size,
   return nullptr;
 }
 
-void FreeListCategory::Free(FreeSpace* free_space, size_t size_in_bytes,
+void FreeListCategory::Free(Address start, size_t size_in_bytes,
                             FreeMode mode) {
-  CHECK(page()->CanAllocate());
+  DCHECK(page()->CanAllocate());
+  FreeSpace* free_space = FreeSpace::cast(HeapObject::FromAddress(start));
   free_space->set_next(top());
   set_top(free_space);
   available_ += size_in_bytes;
@@ -2686,7 +2792,7 @@ void FreeListCategory::Relink() {
   owner()->AddCategory(this);
 }
 
-FreeList::FreeList(PagedSpace* owner) : owner_(owner), wasted_bytes_(0) {
+FreeList::FreeList() : wasted_bytes_(0) {
   for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
     categories_[i] = nullptr;
   }
@@ -2704,11 +2810,6 @@ void FreeList::Reset() {
 }
 
 size_t FreeList::Free(Address start, size_t size_in_bytes, FreeMode mode) {
-  if (size_in_bytes == 0) return 0;
-
-  owner()->heap()->CreateFillerObjectAt(start, static_cast<int>(size_in_bytes),
-                                        ClearRecordedSlots::kNo);
-
   Page* page = Page::FromAddress(start);
   page->DecreaseAllocatedBytes(size_in_bytes);
 
@@ -2719,11 +2820,10 @@ size_t FreeList::Free(Address start, size_t size_in_bytes, FreeMode mode) {
     return size_in_bytes;
   }
 
-  FreeSpace* free_space = FreeSpace::cast(HeapObject::FromAddress(start));
   // Insert other blocks at the head of a free list of the appropriate
   // magnitude.
   FreeListCategoryType type = SelectFreeListCategoryType(size_in_bytes);
-  page->free_list_category(type)->Free(free_space, size_in_bytes, mode);
+  page->free_list_category(type)->Free(start, size_in_bytes, mode);
   DCHECK_EQ(page->AvailableInFreeList(),
             page->AvailableInFreeListFromAllocatedBytes());
   return 0;
diff --git a/deps/v8/src/heap/spaces.h b/deps/v8/src/heap/spaces.h
index 08fef7d6e3..1c8bad8dc5 100644
--- a/deps/v8/src/heap/spaces.h
+++ b/deps/v8/src/heap/spaces.h
@@ -139,6 +139,8 @@ enum FreeListCategoryType {
 
 enum FreeMode { kLinkCategory, kDoNotLinkCategory };
 
+enum class SpaceAccountingMode { kSpaceAccounted, kSpaceUnaccounted };
+
 enum RememberedSetType {
   OLD_TO_NEW,
   OLD_TO_OLD,
@@ -148,15 +150,10 @@ enum RememberedSetType {
 // A free list category maintains a linked list of free memory blocks.
 class FreeListCategory {
  public:
-  static const int kSize = kIntSize +      // FreeListCategoryType type_
-                           kIntSize +      // padding for type_
-                           kSizetSize +    // size_t available_
-                           kPointerSize +  // FreeSpace* top_
-                           kPointerSize +  // FreeListCategory* prev_
-                           kPointerSize;   // FreeListCategory* next_
-
-  FreeListCategory()
-      : type_(kInvalidCategory),
+  FreeListCategory(FreeList* free_list, Page* page)
+      : free_list_(free_list),
+        page_(page),
+        type_(kInvalidCategory),
         available_(0),
         top_(nullptr),
         prev_(nullptr),
@@ -180,7 +177,7 @@ class FreeListCategory {
   // category is currently unlinked.
   void Relink();
 
-  void Free(FreeSpace* node, size_t size_in_bytes, FreeMode mode);
+  void Free(Address address, size_t size_in_bytes, FreeMode mode);
 
   // Picks a node from the list and stores its size in |node_size|. Returns
   // nullptr if the category is empty.
@@ -196,11 +193,13 @@ class FreeListCategory {
   FreeSpace* SearchForNodeInList(size_t minimum_size, size_t* node_size);
 
   inline FreeList* owner();
-  inline Page* page() const;
+  inline Page* page() const { return page_; }
   inline bool is_linked();
   bool is_empty() { return top() == nullptr; }
   size_t available() const { return available_; }
 
+  void set_free_list(FreeList* free_list) { free_list_ = free_list; }
+
 #ifdef DEBUG
   size_t SumFreeList();
   int FreeListLength();
@@ -218,6 +217,12 @@ class FreeListCategory {
   FreeListCategory* next() { return next_; }
   void set_next(FreeListCategory* next) { next_ = next; }
 
+  // This FreeListCategory is owned by the given free_list_.
+  FreeList* free_list_;
+
+  // This FreeListCategory holds free list entries of the given page_.
+  Page* const page_;
+
   // |type_|: The type of this free list category.
   FreeListCategoryType type_;
 
@@ -233,6 +238,8 @@ class FreeListCategory {
 
   friend class FreeList;
   friend class PagedSpace;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(FreeListCategory);
 };
 
 // MemoryChunk represents a memory region owned by a specific space.
@@ -370,7 +377,7 @@ class MemoryChunk {
       + kSizetSize    // size_t wasted_memory_
       + kPointerSize  // AtomicValue next_chunk_
       + kPointerSize  // AtomicValue prev_chunk_
-      + FreeListCategory::kSize * kNumberOfCategories
+      + kPointerSize * kNumberOfCategories
       // FreeListCategory categories_[kNumberOfCategories]
       + kPointerSize   // LocalArrayBufferTracker* local_tracker_
       + kIntptrSize    // intptr_t young_generation_live_byte_count_
@@ -610,6 +617,8 @@ class MemoryChunk {
 
   void set_owner(Space* space) { owner_.SetValue(space); }
 
+  bool IsPagedSpace() const;
+
   void InsertAfter(MemoryChunk* other);
   void Unlink();
 
@@ -620,8 +629,6 @@ class MemoryChunk {
   void SetReadAndExecutable();
   void SetReadAndWritable();
 
-  inline void InitializeFreeListCategories();
-
  protected:
   static MemoryChunk* Initialize(Heap* heap, Address base, size_t size,
                                  Address area_start, Address area_end,
@@ -699,7 +706,7 @@ class MemoryChunk {
   // prev_chunk_ holds a pointer of type MemoryChunk
   base::AtomicValue<MemoryChunk*> prev_chunk_;
 
-  FreeListCategory categories_[kNumberOfCategories];
+  FreeListCategory* categories_[kNumberOfCategories];
 
   LocalArrayBufferTracker* local_tracker_;
 
@@ -788,7 +795,7 @@ class Page : public MemoryChunk {
   template <typename Callback>
   inline void ForAllFreeListCategories(Callback callback) {
     for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
-      callback(&categories_[i]);
+      callback(categories_[i]);
     }
   }
 
@@ -820,7 +827,7 @@ class Page : public MemoryChunk {
   }
 
   FreeListCategory* free_list_category(FreeListCategoryType type) {
-    return &categories_[type];
+    return categories_[type];
   }
 
   bool is_anchor() { return IsFlagSet(Page::ANCHOR); }
@@ -845,6 +852,10 @@ class Page : public MemoryChunk {
   V8_EXPORT_PRIVATE void CreateBlackArea(Address start, Address end);
   void DestroyBlackArea(Address start, Address end);
 
+  void InitializeFreeListCategories();
+  void AllocateFreeListCategories();
+  void ReleaseFreeListCategories();
+
 #ifdef DEBUG
   void Print();
 #endif  // DEBUG
@@ -1170,14 +1181,14 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
         : heap_(heap),
           allocator_(allocator),
           pending_unmapping_tasks_semaphore_(0),
-          concurrent_unmapping_tasks_active_(0) {
+          pending_unmapping_tasks_(0),
+          active_unmapping_tasks_(0) {
       chunks_[kRegular].reserve(kReservedQueueingSlots);
       chunks_[kPooled].reserve(kReservedQueueingSlots);
     }
 
     void AddMemoryChunkSafe(MemoryChunk* chunk) {
-      if ((chunk->size() == Page::kPageSize) &&
-          (chunk->executable() != EXECUTABLE)) {
+      if (chunk->IsPagedSpace() && chunk->executable() != EXECUTABLE) {
         AddMemoryChunkSafe<kRegular>(chunk);
       } else {
         AddMemoryChunkSafe<kNonRegular>(chunk);
@@ -1238,6 +1249,8 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
       return chunk;
     }
 
+    bool MakeRoomForNewTasks();
+
     template <FreeMode mode>
     void PerformFreeMemoryOnQueuedChunks();
 
@@ -1247,7 +1260,8 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
     std::vector<MemoryChunk*> chunks_[kNumberOfChunkQueues];
     CancelableTaskManager::Id task_ids_[kMaxUnmapperTasks];
     base::Semaphore pending_unmapping_tasks_semaphore_;
-    intptr_t concurrent_unmapping_tasks_active_;
+    intptr_t pending_unmapping_tasks_;
+    base::AtomicNumber<intptr_t> active_unmapping_tasks_;
 
     friend class MemoryAllocator;
   };
@@ -1359,6 +1373,12 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
   // and false otherwise.
   bool CommitBlock(Address start, size_t size, Executability executable);
 
+  // Checks if an allocated MemoryChunk was intended to be used for executable
+  // memory.
+  bool IsMemoryChunkExecutable(MemoryChunk* chunk) {
+    return executable_memory_.find(chunk) != executable_memory_.end();
+  }
+
   // Uncommit a contiguous block of memory [start..(start+size)[.
   // start is not nullptr, the size is greater than zero, and the
   // block is contained in the initial chunk.  Returns true if it succeeded
@@ -1409,6 +1429,17 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
     } while ((high > ptr) && !highest_ever_allocated_.TrySetValue(ptr, high));
   }
 
+  void RegisterExecutableMemoryChunk(MemoryChunk* chunk) {
+    DCHECK(chunk->IsFlagSet(MemoryChunk::IS_EXECUTABLE));
+    DCHECK_EQ(executable_memory_.find(chunk), executable_memory_.end());
+    executable_memory_.insert(chunk);
+  }
+
+  void UnregisterExecutableMemoryChunk(MemoryChunk* chunk) {
+    DCHECK_NE(executable_memory_.find(chunk), executable_memory_.end());
+    executable_memory_.erase(chunk);
+  }
+
   Isolate* isolate_;
   CodeRange* code_range_;
 
@@ -1431,6 +1462,9 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
   VirtualMemory last_chunk_;
   Unmapper unmapper_;
 
+  // Data structure to remember allocated executable memory chunks.
+  std::unordered_set<MemoryChunk*> executable_memory_;
+
   friend class heap::TestCodeRangeScope;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(MemoryAllocator);
@@ -1731,7 +1765,7 @@ class V8_EXPORT_PRIVATE FreeList {
     return kHuge;
   }
 
-  explicit FreeList(PagedSpace* owner);
+  FreeList();
 
   // Adds a node on the free list. The block of size {size_in_bytes} starting
   // at {start} is placed on the free list. The return value is the number of
@@ -1779,7 +1813,6 @@ class V8_EXPORT_PRIVATE FreeList {
   size_t EvictFreeListItems(Page* page);
   bool ContainsPageFreeListItems(Page* page);
 
-  PagedSpace* owner() { return owner_; }
   size_t wasted_bytes() { return wasted_bytes_.Value(); }
 
   template <typename Callback>
@@ -1874,13 +1907,10 @@ class V8_EXPORT_PRIVATE FreeList {
     return categories_[type];
   }
 
-  PagedSpace* owner_;
   base::AtomicNumber<size_t> wasted_bytes_;
   FreeListCategory* categories_[kNumberOfCategories];
 
   friend class FreeListCategory;
-
-  DISALLOW_IMPLICIT_CONSTRUCTORS(FreeList);
 };
 
 // LocalAllocationBuffer represents a linear allocation area that is created
@@ -2086,11 +2116,22 @@ class V8_EXPORT_PRIVATE PagedSpace
   MUST_USE_RESULT inline AllocationResult AllocateRaw(
       int size_in_bytes, AllocationAlignment alignment);
 
+  size_t Free(Address start, size_t size_in_bytes, SpaceAccountingMode mode) {
+    if (size_in_bytes == 0) return 0;
+    heap_->CreateFillerObjectAt(start, static_cast<int>(size_in_bytes),
+                                ClearRecordedSlots::kNo);
+    if (mode == SpaceAccountingMode::kSpaceAccounted) {
+      return AccountedFree(start, size_in_bytes);
+    } else {
+      return UnaccountedFree(start, size_in_bytes);
+    }
+  }
+
   // Give a block of memory to the space's free list.  It might be added to
   // the free list or accounted as waste.
   // If add_to_freelist is false then just accounting stats are updated and
   // no attempt to add area to free list is made.
-  size_t Free(Address start, size_t size_in_bytes) {
+  size_t AccountedFree(Address start, size_t size_in_bytes) {
     size_t wasted = free_list_.Free(start, size_in_bytes, kLinkCategory);
     Page* page = Page::FromAddress(start);
     accounting_stats_.DecreaseAllocatedBytes(size_in_bytes, page);
diff --git a/deps/v8/src/heap/store-buffer.h b/deps/v8/src/heap/store-buffer.h
index a69abcc886..58f47f4834 100644
--- a/deps/v8/src/heap/store-buffer.h
+++ b/deps/v8/src/heap/store-buffer.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_STORE_BUFFER_H_
-#define V8_STORE_BUFFER_H_
+#ifndef V8_HEAP_STORE_BUFFER_H_
+#define V8_HEAP_STORE_BUFFER_H_
 
 #include "src/allocation.h"
 #include "src/base/logging.h"
@@ -225,4 +225,4 @@ class StoreBuffer {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_STORE_BUFFER_H_
+#endif  // V8_HEAP_STORE_BUFFER_H_
diff --git a/deps/v8/src/heap/stress-marking-observer.h b/deps/v8/src/heap/stress-marking-observer.h
index b97c2b179c..37ebb82197 100644
--- a/deps/v8/src/heap/stress-marking-observer.h
+++ b/deps/v8/src/heap/stress-marking-observer.h
@@ -23,4 +23,4 @@ class StressMarkingObserver : public AllocationObserver {
 }  // namespace internal
 }  // namespace v8
 
-#endif
+#endif  // V8_HEAP_STRESS_MARKING_OBSERVER_H_
diff --git a/deps/v8/src/heap/stress-scavenge-observer.h b/deps/v8/src/heap/stress-scavenge-observer.h
index 6f69afe4c5..b39b2eac59 100644
--- a/deps/v8/src/heap/stress-scavenge-observer.h
+++ b/deps/v8/src/heap/stress-scavenge-observer.h
@@ -36,4 +36,4 @@ class StressScavengeObserver : public AllocationObserver {
 }  // namespace internal
 }  // namespace v8
 
-#endif
+#endif  // V8_HEAP_STRESS_SCAVENGE_OBSERVER_H_
diff --git a/deps/v8/src/heap/sweeper.cc b/deps/v8/src/heap/sweeper.cc
index 25ba0df8fd..2072e407e9 100644
--- a/deps/v8/src/heap/sweeper.cc
+++ b/deps/v8/src/heap/sweeper.cc
@@ -279,8 +279,8 @@ int Sweeper::RawSweep(Page* p, FreeListRebuildingMode free_list_mode,
         memset(free_start, 0xCC, size);
       }
       if (free_list_mode == REBUILD_FREE_LIST) {
-        freed_bytes = reinterpret_cast<PagedSpace*>(space)->UnaccountedFree(
-            free_start, size);
+        freed_bytes = reinterpret_cast<PagedSpace*>(space)->Free(
+            free_start, size, SpaceAccountingMode::kSpaceUnaccounted);
         max_freed_bytes = Max(freed_bytes, max_freed_bytes);
       } else {
         p->heap()->CreateFillerObjectAt(free_start, static_cast<int>(size),
@@ -318,8 +318,8 @@ int Sweeper::RawSweep(Page* p, FreeListRebuildingMode free_list_mode,
       memset(free_start, 0xCC, size);
     }
     if (free_list_mode == REBUILD_FREE_LIST) {
-      freed_bytes = reinterpret_cast<PagedSpace*>(space)->UnaccountedFree(
-          free_start, size);
+      freed_bytes = reinterpret_cast<PagedSpace*>(space)->Free(
+          free_start, size, SpaceAccountingMode::kSpaceUnaccounted);
       max_freed_bytes = Max(freed_bytes, max_freed_bytes);
     } else {
       p->heap()->CreateFillerObjectAt(free_start, static_cast<int>(size),
diff --git a/deps/v8/src/heap/worklist.h b/deps/v8/src/heap/worklist.h
index 3421e16611..bb3eae2228 100644
--- a/deps/v8/src/heap/worklist.h
+++ b/deps/v8/src/heap/worklist.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_HEAP_WORKLIST_
-#define V8_HEAP_WORKLIST_
+#ifndef V8_HEAP_WORKLIST_H_
+#define V8_HEAP_WORKLIST_H_
 
 #include <cstddef>
 #include <utility>
@@ -388,4 +388,4 @@ class Worklist {
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_HEAP_WORKLIST_
+#endif  // V8_HEAP_WORKLIST_H_