Oilpan: Introduce memory pool for CallbackStacks

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

Index: third_party/WebKit/Source/platform/heap/ThreadState.cpp
diff --git a/third_party/WebKit/Source/platform/heap/ThreadState.cpp b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
index 4b975f7563be186de4180620a0a86bc2c6d30bfa..72e4e2b531526f129009d941ee43b67b9e9645bb 100644
--- a/third_party/WebKit/Source/platform/heap/ThreadState.cpp
+++ b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
@@ -136,10 +136,7 @@ ThreadState::ThreadState(bool perThreadHeapEnabled)
     m_likelyToBePromptlyFreed = wrapArrayUnique(new int[likelyToBePromptlyFreedArraySize]);
     clearArenaAges();
 
-    // There is little use of weak references and collections off the main thread;
-    // use a much lower initial block reservation.
-    size_t initialBlockSize = isMainThread() ? CallbackStack::kDefaultBlockSize : CallbackStack::kMinimalBlockSize;
-    m_threadLocalWeakCallbackStack = new CallbackStack(initialBlockSize);
+    m_threadLocalWeakCallbackStack = new CallbackStack();
 }
 
 ThreadState::~ThreadState()
@@ -963,7 +960,8 @@ void ThreadState::preGC()
     // should only process callbacks that's found to be reachable by
     // the latest GC, when it eventually gets to next perform
     // thread-local weak processing.
-    m_threadLocalWeakCallbackStack->clear();
+    m_threadLocalWeakCallbackStack->decommit();

[sof, 2016/07/05 14:19:02]

Naming this clear() or reset() would be clearer, perhaps.

But, wouldn't it make sense to decommit the thread-local stack after having
completed the thread-local weak processing? If not, don't you risk having N
threads holding on to a pooled stack, but the GCing thread having to commit &
allocate its stacks from somewhere else.

[haraken, 2016/07/06 01:58:11]

We're already calling decommit() at the end of
ThreadState::threadLocalWeakProcessing().

I'd prefer "commit"/"decommit" to make the function names balanced (V8 is using
the names).

[sof, 2016/07/06 13:22:17]

Ah, of course we already are; good.
ok.

+    m_threadLocalWeakCallbackStack->commit();
 }
 
 void ThreadState::postGC(BlinkGC::GCType gcType)