Oilpan: Decommit backing storage of CallbackStacks

third_party/WebKit/Source/platform/heap/Heap.cpp

Index: third_party/WebKit/Source/platform/heap/Heap.cpp
diff --git a/third_party/WebKit/Source/platform/heap/Heap.cpp b/third_party/WebKit/Source/platform/heap/Heap.cpp
index 8a414e3ec0378d68a144275f1cf59b6561e47c60..5f2809b0fde544c5063643db8588a1cc4ac1e092 100644
--- a/third_party/WebKit/Source/platform/heap/Heap.cpp
+++ b/third_party/WebKit/Source/platform/heap/Heap.cpp
@@ -355,6 +355,14 @@ bool Heap::weakTableRegistered(const void* table)
 }
 #endif
 
+void Heap::decommitCallbackStacks()
+{
+    s_markingStack->decommit();

[sof, 2016/02/24 09:29:39]

An alternative scheme would be for Heap to reserve memory for all the initial
CallbackStacks in one chunk & then create the stacks with initial blocks set up
to offset into that reserved block.

That way you could decommit the chunk in one operation, and free
CallbackStack::Block from having to decommit themselves individually. Any extra
blocks needed by a CallbackStack would then not be allocated in
"decommittable-memory", which is "fine" (assuming any allocation like this is
acceptable during marking) as they'll be deallocated shortly thereafter anyway.

+    s_postMarkingCallbackStack->decommit();
+    s_globalWeakCallbackStack->decommit();
+    s_ephemeronStack->decommit();
+}
+
 void Heap::preGC()
 {
     ASSERT(!ThreadState::current()->isInGC());
@@ -469,6 +477,7 @@ void Heap::collectGarbage(BlinkGC::StackState stackState, BlinkGC::GCType gcType
     WTF::Partitions::reportMemoryUsageHistogram();
 
     postGC(gcType);
+    Heap::decommitCallbackStacks();
 
 #if ENABLE(ASSERT)
     // 0 is used to figure non-assigned area, so avoid to use 0 in s_gcGeneration.
@@ -511,6 +520,7 @@ void Heap::collectGarbageForTerminatingThread(ThreadState* state)
         globalWeakProcessing(gcScope.visitor());
 
         state->postGC(BlinkGC::GCWithSweep);
+        Heap::decommitCallbackStacks();
     }
     state->preSweep();
 }
@@ -547,8 +557,6 @@ void Heap::postMarkingProcessing(Visitor* visitor)
     //    if they are only reachable from their front objects.
     while (popAndInvokePostMarkingCallback(visitor)) { }
 
-    s_ephemeronStack->clear();
-
     // Post-marking callbacks should not trace any objects and
     // therefore the marking stack should be empty after the
     // post-marking callbacks.