[heap] Lower external allocation limit when external memory shrinks.

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 10022 matching lines @@
   return I::kNumIsolateDataSlots;
 }
 
 
 int64_t Isolate::AdjustAmountOfExternalAllocatedMemory(
     int64_t change_in_bytes) {
   const int64_t kMemoryReducerActivationLimit = 1024 * 1024;
   typedef internal::Internals I;
   int64_t* external_memory = reinterpret_cast<int64_t*>(
       reinterpret_cast<uint8_t*>(this) + I::kExternalMemoryOffset);
-  const int64_t external_memory_limit = *reinterpret_cast<int64_t*>(
+  int64_t* external_memory_limit = reinterpret_cast<int64_t*>(
       reinterpret_cast<uint8_t*>(this) + I::kExternalMemoryLimitOffset);
   int64_t* external_memory_at_last_mc =
       reinterpret_cast<int64_t*>(reinterpret_cast<uint8_t*>(this) +
                                  I::kExternalMemoryAtLastMarkCompactOffset);
   const int64_t amount = *external_memory + change_in_bytes;
 
   *external_memory = amount;
 
   int64_t allocation_diff_since_last_mc =
       *external_memory_at_last_mc - *external_memory;
   allocation_diff_since_last_mc = allocation_diff_since_last_mc < 0
                                       ? -allocation_diff_since_last_mc
                                       : allocation_diff_since_last_mc;
   if (allocation_diff_since_last_mc > kMemoryReducerActivationLimit) {
     CheckMemoryPressure();
   }
 
-  if (change_in_bytes > 0 && amount > external_memory_limit) {
+  if (change_in_bytes < 0) {
+    *external_memory_limit += change_in_bytes;
+  }
+
+  if (change_in_bytes > 0 && amount > *external_memory_limit) {
     ReportExternalAllocationLimitReached();
   }
   return *external_memory;
 }
 
 Local<Value> Context::GetEmbedderData(int index) {
 #ifndef V8_ENABLE_CHECKS
   typedef internal::Object O;
   typedef internal::HeapObject HO;
   typedef internal::Internals I;
@@ skipping 126 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // INCLUDE_V8_H_