[Tracing] Add hook to PartitionAlloc for heap profiling

third_party/WebKit/Source/wtf/PartitionAlloc.cpp

Index: third_party/WebKit/Source/wtf/PartitionAlloc.cpp
diff --git a/third_party/WebKit/Source/wtf/PartitionAlloc.cpp b/third_party/WebKit/Source/wtf/PartitionAlloc.cpp
index d076568fcfc59bd6984d319884c0c6c19b18d6af..f78112afbbd19d229a650e9827a815c94839ba13 100644
--- a/third_party/WebKit/Source/wtf/PartitionAlloc.cpp
+++ b/third_party/WebKit/Source/wtf/PartitionAlloc.cpp
@@ -61,6 +61,9 @@ PartitionPage PartitionRootBase::gSeedPage;
 PartitionBucket PartitionRootBase::gPagedBucket;
 void (*PartitionRootBase::gOomHandlingFunction)() = nullptr;
 
+void (*partitionAllocHookAlloc)(void* addr, size_t size) = nullptr;
+void (*partitionAllocHookFree)(void* addr) = nullptr;
+
 static uint16_t partitionBucketNumSystemPages(size_t size)
 {
     // This works out reasonably for the current bucket sizes of the generic
@@ -1060,8 +1063,16 @@ void* partitionReallocGeneric(PartitionRootGeneric* root, void* ptr, size_t newS
         // We may be able to perform the realloc in place by changing the
         // accessibility of memory pages and, if reducing the size, decommitting
         // them.
-        if (partitionReallocDirectMappedInPlace(root, page, newSize))
+        if (partitionReallocDirectMappedInPlace(root, page, newSize)) {
+            // Report a realloc as a free followed by alloc when heap profiling
+            // is enabled.
+            if (UNLIKELY(partitionAllocHookAlloc && partitionAllocHookFree)) {

[Primiano Tucci (use gerrit), 2015/10/12 16:36:46]

just check one of them. You always set/reset them in couples, not worth spending
time checking both.
In the very worst case (if really you end up setting only one hook) you will
crash and it will be very visible :)

[Ruud van Asseldonk, 2015/10/13 10:42:18]

My reasoning was that an allocation could be happening while the hooks are being
set, but now that I think of it, the correct way to handle that would be to
store the values in a local variable and call those. Though I think the compiler
will only emit a single read here because the variables are not volatile. What
do you think?

[Primiano Tucci (use gerrit), 2015/10/14 10:10:12]

After discussion offline, I think you want to just cache these two in a local
variable (one each) and null check them before calling them

+                partitionAllocHookFree(ptr);
+                partitionAllocHookAlloc(ptr, newSize);
+            }
+
             return ptr;
+        }
     }
 
     size_t actualNewSize = partitionAllocActualSize(root, newSize);
@@ -1085,6 +1096,14 @@ void* partitionReallocGeneric(PartitionRootGeneric* root, void* ptr, size_t newS
 
     memcpy(ret, ptr, copySize);
     partitionFreeGeneric(root, ptr);
+
+    // Report a realloc as a free followed by alloc when heap profiling is
+    // enabled.

[Primiano Tucci (use gerrit), 2015/10/12 16:36:46]

ditto

+    if (UNLIKELY(partitionAllocHookAlloc && partitionAllocHookFree)) {
+        partitionAllocHookFree(ptr);
+        partitionAllocHookAlloc(ret, newSize);
+    }
+
     return ret;
 #endif
 }