1 files changed, 27 insertions, 0 deletions
diff --git a/deps/v8/src/base/platform/platform-cygwin.cc b/deps/v8/src/base/platform/platform-cygwin.cc
index c5d94fc6ba..f2976301ed 100644
--- a/deps/v8/src/base/platform/platform-cygwin.cc
+++ b/deps/v8/src/base/platform/platform-cygwin.cc
@@ -172,6 +172,33 @@ bool OS::SetPermissions(void* address, size_t size, MemoryPermission access) {
 }
 
 // static
+bool OS::DiscardSystemPages(void* address, size_t size) {
+  // On Windows, discarded pages are not returned to the system immediately and
+  // not guaranteed to be zeroed when returned to the application.
+  using DiscardVirtualMemoryFunction =
+      DWORD(WINAPI*)(PVOID virtualAddress, SIZE_T size);
+  static std::atomic<DiscardVirtualMemoryFunction> discard_virtual_memory(
+      reinterpret_cast<DiscardVirtualMemoryFunction>(-1));
+  if (discard_virtual_memory ==
+      reinterpret_cast<DiscardVirtualMemoryFunction>(-1))
+    discard_virtual_memory =
+        reinterpret_cast<DiscardVirtualMemoryFunction>(GetProcAddress(
+            GetModuleHandle(L"Kernel32.dll"), "DiscardVirtualMemory"));
+  // Use DiscardVirtualMemory when available because it releases faster than
+  // MEM_RESET.
+  DiscardVirtualMemoryFunction discard_function = discard_virtual_memory.load();
+  if (discard_function) {
+    DWORD ret = discard_function(address, size);
+    if (!ret) return true;
+  }
+  // DiscardVirtualMemory is buggy in Win10 SP0, so fall back to MEM_RESET on
+  // failure.
+  void* ptr = VirtualAlloc(address, size, MEM_RESET, PAGE_READWRITE);
+  CHECK(ptr);
+  return ptr;
+}
+
+// static
 bool OS::HasLazyCommits() {
   // TODO(alph): implement for the platform.
   return false;