Report DOM partitionAlloc size to V8 GC.

Source/wtf/PartitionAlloc.h

Index: Source/wtf/PartitionAlloc.h
diff --git a/Source/wtf/PartitionAlloc.h b/Source/wtf/PartitionAlloc.h
index 74871483107e1b6dff4e01454d7f9dfb07605085..c0709d9d62b1e200e83aa112513ee0395bb5e65c 100644
--- a/Source/wtf/PartitionAlloc.h
+++ b/Source/wtf/PartitionAlloc.h
@@ -254,6 +254,7 @@ struct PartitionSuperPageExtentEntry {
 };
 
 struct WTF_EXPORT PartitionRootBase {
+    size_t totalAllocationSize;
     size_t totalSizeOfSuperPages;
     unsigned numBuckets;
     unsigned maxAllocation;
@@ -464,6 +465,7 @@ ALWAYS_INLINE void* partitionBucketAlloc(PartitionRootBase* root, int flags, siz
     // The value given to the application is actually just after the cookie.
     ret = static_cast<char*>(ret) + kCookieSize;
 #endif
+    root->totalAllocationSize += bucket->slotSize;

[Chris Evans, 2014/06/05 18:00:26]

My gut reaction is I don't like this. It adds overhead to the (insanely
optimized) fast paths. Can we find a solution that is slow path only? Maybe the
number of active + full pages (i.e. resident system pages) is a good
approximation.

In fact it might even be better, as it will cause gc pressure on v8 if we have a
low allocation count but high fragmentation.

     return ret;
 }
 
@@ -487,8 +489,8 @@ ALWAYS_INLINE void* partitionAlloc(PartitionRoot* root, size_t size)
 ALWAYS_INLINE void partitionFreeWithPage(void* ptr, PartitionPage* page)
 {
     // If these asserts fire, you probably corrupted memory.
-#ifndef NDEBUG
     size_t bucketSize = page->bucket->slotSize;
+#ifndef NDEBUG
     partitionCookieCheckValue(ptr);
     partitionCookieCheckValue(reinterpret_cast<char*>(ptr) + bucketSize - kCookieSize);
     memset(ptr, kFreedByte, bucketSize);
@@ -502,6 +504,10 @@ ALWAYS_INLINE void partitionFreeWithPage(void* ptr, PartitionPage* page)
     entry->next = partitionFreelistMask(freelistHead);
     page->freelistHead = entry;
     --page->numAllocatedSlots;
+
+    PartitionRootBase* root = partitionPageToRoot(page);
+    root->totalAllocationSize -= bucketSize;

[Tom Sepez, 2014/06/05 17:52:01]

nit: assert you don't underflow here.

+
     if (UNLIKELY(page->numAllocatedSlots <= 0))
         partitionFreeSlowPath(page);
 }