v8,src: expose statistics about heap spaces

Provide means to inspect information about the separate heap spaces
via a callable API. This is helpful to analyze memory issues.

Fixes: https://github.com/nodejs/node/issues/2079
PR-URL: https://github.com/nodejs/node/pull/4463
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

6 files changed, 202 insertions, 2 deletions

diff --git a/doc/api/v8.markdown b/doc/api/v8.markdown
index 70abd6c647..c6d760b0d5 100644
--- a/doc/api/v8.markdown
+++ b/doc/api/v8.markdown
@@ -21,6 +21,55 @@ Returns an object with the following properties
 }
 ```
 
+## getHeapSpaceStatistics()
+
+Returns statistics about the V8 heap spaces, i.e. the segments which make up
+the V8 heap. Order of heap spaces nor availability of a heap space can be
+guaranteed as the statistics are provided via the V8 `GetHeapSpaceStatistics`
+function.
+
+Example result:
+
+```
+[
+  {
+    "space_name": "new_space",
+    "space_size": 2063872,
+    "space_used_size": 951112,
+    "space_available_size": 80824,
+    "physical_space_size": 2063872
+  },
+  {
+    "space_name": "old_space",
+    "space_size": 3090560,
+    "space_used_size": 2493792,
+    "space_available_size": 0,
+    "physical_space_size": 3090560
+  },
+  {
+    "space_name": "code_space",
+    "space_size": 1260160,
+    "space_used_size": 644256,
+    "space_available_size": 960,
+    "physical_space_size": 1260160
+  },
+  {
+    "space_name": "map_space",
+    "space_size": 1094160,
+    "space_used_size": 201608,
+    "space_available_size": 0,
+    "physical_space_size": 1094160
+  },
+  {
+    "space_name": "large_object_space",
+    "space_size": 0,
+    "space_used_size": 0,
+    "space_available_size": 1490980608,
+    "physical_space_size": 0
+  }
+]
+```
+
 ## setFlagsFromString(string)
 
 Set additional V8 command line flags.  Use with care; changing settings
diff --git a/lib/v8.js b/lib/v8.js
index acadfa64e0..551b2ada98 100644
--- a/lib/v8.js
+++ b/lib/v8.js
@@ -16,9 +16,9 @@
 
 const v8binding = process.binding('v8');
 
+// Properties for heap statistics buffer extraction.
 const heapStatisticsBuffer =
     new Uint32Array(v8binding.heapStatisticsArrayBuffer);
-
 const kTotalHeapSizeIndex = v8binding.kTotalHeapSizeIndex;
 const kTotalHeapSizeExecutableIndex = v8binding.kTotalHeapSizeExecutableIndex;
 const kTotalPhysicalSizeIndex = v8binding.kTotalPhysicalSizeIndex;
@@ -26,6 +26,18 @@ const kTotalAvailableSize = v8binding.kTotalAvailableSize;
 const kUsedHeapSizeIndex = v8binding.kUsedHeapSizeIndex;
 const kHeapSizeLimitIndex = v8binding.kHeapSizeLimitIndex;
 
+// Properties for heap space statistics buffer extraction.
+const heapSpaceStatisticsBuffer =
+    new Uint32Array(v8binding.heapSpaceStatisticsArrayBuffer);
+const kHeapSpaces = v8binding.kHeapSpaces;
+const kNumberOfHeapSpaces = kHeapSpaces.length;
+const kHeapSpaceStatisticsPropertiesCount =
+    v8binding.kHeapSpaceStatisticsPropertiesCount;
+const kSpaceSizeIndex = v8binding.kSpaceSizeIndex;
+const kSpaceUsedSizeIndex = v8binding.kSpaceUsedSizeIndex;
+const kSpaceAvailableSizeIndex = v8binding.kSpaceAvailableSizeIndex;
+const kPhysicalSpaceSizeIndex = v8binding.kPhysicalSpaceSizeIndex;
+
 exports.getHeapStatistics = function() {
   const buffer = heapStatisticsBuffer;
 
@@ -42,3 +54,22 @@ exports.getHeapStatistics = function() {
 };
 
 exports.setFlagsFromString = v8binding.setFlagsFromString;
+
+exports.getHeapSpaceStatistics = function() {
+  const heapSpaceStatistics = new Array(kNumberOfHeapSpaces);
+  const buffer = heapSpaceStatisticsBuffer;
+  v8binding.updateHeapSpaceStatisticsArrayBuffer();
+
+  for (let i = 0; i < kNumberOfHeapSpaces; i++) {
+    const propertyOffset = i * kHeapSpaceStatisticsPropertiesCount;
+    heapSpaceStatistics[i] = {
+      space_name: kHeapSpaces[i],
+      space_size: buffer[propertyOffset + kSpaceSizeIndex],
+      space_used_size: buffer[propertyOffset + kSpaceUsedSizeIndex],
+      space_available_size: buffer[propertyOffset + kSpaceAvailableSizeIndex],
+      physical_space_size: buffer[propertyOffset + kPhysicalSpaceSizeIndex]
+    };
+  }
+
+  return heapSpaceStatistics;
+};
diff --git a/src/env-inl.h b/src/env-inl.h
index f73e9c6ba2..d2c0e048a6 100644
--- a/src/env-inl.h
+++ b/src/env-inl.h
@@ -242,6 +242,7 @@ inline Environment::~Environment() {
   isolate_data()->Put();
 
   delete[] heap_statistics_buffer_;
+  delete[] heap_space_statistics_buffer_;
   delete[] http_parser_buffer_;
 }
 
@@ -374,6 +375,17 @@ inline void Environment::set_heap_statistics_buffer(uint32_t* pointer) {
   heap_statistics_buffer_ = pointer;
 }
 
+inline uint32_t* Environment::heap_space_statistics_buffer() const {
+  CHECK_NE(heap_space_statistics_buffer_, nullptr);
+  return heap_space_statistics_buffer_;
+}
+
+inline void Environment::set_heap_space_statistics_buffer(uint32_t* pointer) {
+  CHECK_EQ(heap_space_statistics_buffer_, nullptr);  // Should be set only once.
+  heap_space_statistics_buffer_ = pointer;
+}
+
+
 inline char* Environment::http_parser_buffer() const {
   return http_parser_buffer_;
 }
diff --git a/src/env.h b/src/env.h
index 743bf057e8..bb0868e1d8 100644
--- a/src/env.h
+++ b/src/env.h
@@ -462,6 +462,9 @@ class Environment {
   inline uint32_t* heap_statistics_buffer() const;
   inline void set_heap_statistics_buffer(uint32_t* pointer);
 
+  inline uint32_t* heap_space_statistics_buffer() const;
+  inline void set_heap_space_statistics_buffer(uint32_t* pointer);
+
   inline char* http_parser_buffer() const;
   inline void set_http_parser_buffer(char* buffer);
 
@@ -562,6 +565,7 @@ class Environment {
   int handle_cleanup_waiting_;
 
   uint32_t* heap_statistics_buffer_ = nullptr;
+  uint32_t* heap_space_statistics_buffer_ = nullptr;
 
   char* http_parser_buffer_;
 
diff --git a/src/node_v8.cc b/src/node_v8.cc
index 9f456daec4..a1122e57f1 100644
--- a/src/node_v8.cc
+++ b/src/node_v8.cc
@@ -7,13 +7,16 @@
 
 namespace node {
 
+using v8::Array;
 using v8::ArrayBuffer;
 using v8::Context;
 using v8::Function;
 using v8::FunctionCallbackInfo;
+using v8::HeapSpaceStatistics;
 using v8::HeapStatistics;
 using v8::Isolate;
 using v8::Local;
+using v8::NewStringType;
 using v8::Object;
 using v8::String;
 using v8::Uint32;
@@ -34,6 +37,21 @@ static const size_t kHeapStatisticsPropertiesCount =
     HEAP_STATISTICS_PROPERTIES(V);
 #undef V
 
+#define HEAP_SPACE_STATISTICS_PROPERTIES(V)                                   \
+  V(0, space_size, kSpaceSizeIndex)                                           \
+  V(1, space_used_size, kSpaceUsedSizeIndex)                                  \
+  V(2, space_available_size, kSpaceAvailableSizeIndex)                        \
+  V(3, physical_space_size, kPhysicalSpaceSizeIndex)
+
+#define V(a, b, c) +1
+static const size_t kHeapSpaceStatisticsPropertiesCount =
+    HEAP_SPACE_STATISTICS_PROPERTIES(V);
+#undef V
+
+// Will be populated in InitializeV8Bindings.
+static size_t number_of_heap_spaces = 0;
+
+
 void UpdateHeapStatisticsArrayBuffer(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   HeapStatistics s;
@@ -45,6 +63,23 @@ void UpdateHeapStatisticsArrayBuffer(const FunctionCallbackInfo<Value>& args) {
 }
 
 
+void UpdateHeapSpaceStatisticsBuffer(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+  HeapSpaceStatistics s;
+  Isolate* const isolate = env->isolate();
+  uint32_t* buffer = env->heap_space_statistics_buffer();
+
+  for (size_t i = 0; i < number_of_heap_spaces; i++) {
+    isolate->GetHeapSpaceStatistics(&s, i);
+    size_t const property_offset = i * kHeapSpaceStatisticsPropertiesCount;
+#define V(index, name, _) buffer[property_offset + index] = \
+                              static_cast<uint32_t>(s.name());
+      HEAP_SPACE_STATISTICS_PROPERTIES(V)
+#undef V
+  }
+}
+
+
 void SetFlagsFromString(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
@@ -62,10 +97,10 @@ void InitializeV8Bindings(Local<Object> target,
                           Local<Value> unused,
                           Local<Context> context) {
   Environment* env = Environment::GetCurrent(context);
+
   env->SetMethod(target,
                  "updateHeapStatisticsArrayBuffer",
                  UpdateHeapStatisticsArrayBuffer);
-  env->SetMethod(target, "setFlagsFromString", SetFlagsFromString);
 
   env->set_heap_statistics_buffer(new uint32_t[kHeapStatisticsPropertiesCount]);
 
@@ -84,6 +119,56 @@ void InitializeV8Bindings(Local<Object> target,
 
   HEAP_STATISTICS_PROPERTIES(V)
 #undef V
+
+  target->Set(FIXED_ONE_BYTE_STRING(env->isolate(),
+                                    "kHeapSpaceStatisticsPropertiesCount"),
+              Uint32::NewFromUnsigned(env->isolate(),
+                                      kHeapSpaceStatisticsPropertiesCount));
+
+  number_of_heap_spaces = env->isolate()->NumberOfHeapSpaces();
+
+  // Heap space names are extracted once and exposed to JavaScript to
+  // avoid excessive creation of heap space name Strings.
+  HeapSpaceStatistics s;
+  const Local<Array> heap_spaces = Array::New(env->isolate(),
+                                              number_of_heap_spaces);
+  for (size_t i = 0; i < number_of_heap_spaces; i++) {
+    env->isolate()->GetHeapSpaceStatistics(&s, i);
+    Local<String> heap_space_name = String::NewFromUtf8(env->isolate(),
+                                                        s.space_name(),
+                                                        NewStringType::kNormal)
+                                        .ToLocalChecked();
+    heap_spaces->Set(i, heap_space_name);
+  }
+  target->Set(FIXED_ONE_BYTE_STRING(env->isolate(), "kHeapSpaces"),
+              heap_spaces);
+
+  env->SetMethod(target,
+                 "updateHeapSpaceStatisticsArrayBuffer",
+                 UpdateHeapSpaceStatisticsBuffer);
+
+  env->set_heap_space_statistics_buffer(
+    new uint32_t[kHeapSpaceStatisticsPropertiesCount * number_of_heap_spaces]);
+
+  const size_t heap_space_statistics_buffer_byte_length =
+      sizeof(*env->heap_space_statistics_buffer()) *
+      kHeapSpaceStatisticsPropertiesCount *
+      number_of_heap_spaces;
+
+  target->Set(FIXED_ONE_BYTE_STRING(env->isolate(),
+                                    "heapSpaceStatisticsArrayBuffer"),
+              ArrayBuffer::New(env->isolate(),
+                               env->heap_space_statistics_buffer(),
+                               heap_space_statistics_buffer_byte_length));
+
+#define V(i, _, name)                                                         \
+  target->Set(FIXED_ONE_BYTE_STRING(env->isolate(), #name),                   \
+              Uint32::NewFromUnsigned(env->isolate(), i));
+
+  HEAP_SPACE_STATISTICS_PROPERTIES(V)
+#undef V
+
+  env->SetMethod(target, "setFlagsFromString", SetFlagsFromString);
 }
 
 }  // namespace node
diff --git a/test/parallel/test-v8-stats.js b/test/parallel/test-v8-stats.js
index eb5566fe2b..54140e4110 100644
--- a/test/parallel/test-v8-stats.js
+++ b/test/parallel/test-v8-stats.js
@@ -15,3 +15,22 @@ assert.deepEqual(Object.keys(s).sort(), keys);
 keys.forEach(function(key) {
   assert.equal(typeof s[key], 'number');
 });
+
+
+const expectedHeapSpaces = [
+  'new_space',
+  'old_space',
+  'code_space',
+  'map_space',
+  'large_object_space'
+];
+const heapSpaceStatistics = v8.getHeapSpaceStatistics();
+const actualHeapSpaceNames = heapSpaceStatistics.map(s => s.space_name);
+assert.deepEqual(actualHeapSpaceNames.sort(), expectedHeapSpaces.sort());
+heapSpaceStatistics.forEach(heapSpace => {
+  assert.strictEqual(typeof heapSpace.space_name, 'string');
+  assert.strictEqual(typeof heapSpace.space_size, 'number');
+  assert.strictEqual(typeof heapSpace.space_used_size, 'number');
+  assert.strictEqual(typeof heapSpace.space_available_size, 'number');
+  assert.strictEqual(typeof heapSpace.physical_space_size, 'number');
+});