[heap] Activate memory reducer on external memory activity.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 30445457c20638b5cd2512e29649ae370ab7f97f..112fe4c9f07a2f829c1fac1d22111f81266d0bc5 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -7589,6 +7589,7 @@ class V8_EXPORT Isolate {
   friend class PersistentValueMapBase;
 
   void ReportExternalAllocationLimitReached();
+  void CheckMemoryPressure();
 };
 
 class V8_EXPORT StartupData {
@@ -8816,6 +8817,8 @@ class Internals {
   static const int kExternalMemoryOffset = 4 * kApiPointerSize;
   static const int kExternalMemoryLimitOffset =
       kExternalMemoryOffset + kApiInt64Size;
+  static const int kExternalMemoryAtLastMarkCompactOffset =
+      kExternalMemoryLimitOffset + kApiInt64Size;
   static const int kIsolateRootsOffset = kExternalMemoryLimitOffset +
                                          kApiInt64Size + kApiInt64Size +
                                          kApiPointerSize + kApiPointerSize;
@@ -10033,13 +10036,28 @@ uint32_t Isolate::GetNumberOfDataSlots() {
 
 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*>(
       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) {
     ReportExternalAllocationLimitReached();
   }