[heap] Fine-grained JSArrayBuffer tracking

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 52b6192b87643bec0a0abff62dac9864da01baf7..3ef2e025dbc776cd06af1895058a446807bd27ff 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -7343,9 +7343,9 @@ class Internals {
   static const int kAmountOfExternalAllocatedMemoryOffset =
       4 * kApiPointerSize;
   static const int kAmountOfExternalAllocatedMemoryAtLastGlobalGCOffset =
-      kAmountOfExternalAllocatedMemoryOffset + kApiInt64Size;
+      kAmountOfExternalAllocatedMemoryOffset + kApiPointerSize;
   static const int kIsolateRootsOffset =
-      kAmountOfExternalAllocatedMemoryAtLastGlobalGCOffset + kApiInt64Size +
+      kAmountOfExternalAllocatedMemoryAtLastGlobalGCOffset + kApiPointerSize +
       kApiPointerSize;
   static const int kUndefinedValueRootIndex = 4;
   static const int kTheHoleValueRootIndex = 5;
@@ -8552,14 +8552,15 @@ uint32_t Isolate::GetNumberOfDataSlots() {
 int64_t Isolate::AdjustAmountOfExternalAllocatedMemory(
     int64_t change_in_bytes) {
   typedef internal::Internals I;
-  int64_t* amount_of_external_allocated_memory =
-      reinterpret_cast<int64_t*>(reinterpret_cast<uint8_t*>(this) +
-                                 I::kAmountOfExternalAllocatedMemoryOffset);
-  int64_t* amount_of_external_allocated_memory_at_last_global_gc =
-      reinterpret_cast<int64_t*>(
+  intptr_t* amount_of_external_allocated_memory =
+      reinterpret_cast<intptr_t*>(reinterpret_cast<uint8_t*>(this) +
+                                  I::kAmountOfExternalAllocatedMemoryOffset);
+  intptr_t* amount_of_external_allocated_memory_at_last_global_gc =
+      reinterpret_cast<intptr_t*>(

[Michael Lippautz, 2016/05/11 08:22:51]

It's really unfortunate that we require this magic here but experience shows
that we should have this fast path in the header.

Note that we cast an atomic value to intptr_t and use it as a counter. Happy for
any suggestions.

           reinterpret_cast<uint8_t*>(this) +
           I::kAmountOfExternalAllocatedMemoryAtLastGlobalGCOffset);
-  int64_t amount = *amount_of_external_allocated_memory + change_in_bytes;
+  intptr_t amount = *amount_of_external_allocated_memory +
+                    static_cast<intptr_t>(change_in_bytes);
   if (change_in_bytes > 0 &&
       amount - *amount_of_external_allocated_memory_at_last_global_gc >
           I::kExternalAllocationLimit) {