Oilpan: adjust GC policy under memory pressure (only.)

Source/bindings/core/v8/V8GCController.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 364 matching lines @@
         TRACE_EVENT_SET_SAMPLING_STATE("v8", "V8MajorGC");
     } else {
         MajorGCWrapperVisitor visitor(isolate, constructRetainedObjectInfos);
         v8::V8::VisitHandlesWithClassIds(isolate, &visitor);
         visitor.notifyFinished();
     }
 }
 
 void V8GCController::gcEpilogue(v8::GCType type, v8::GCCallbackFlags flags)
 {
+    // v8::kGCCallbackFlagForced forces a Blink heap garbage collection
+    // when a garbage collection was forced from V8. This is either used
+    // for tests that force GCs from JavaScript to verify that objects die
+    // when expected, or when handling memory pressure notifications.
+    bool forceGC = flags & v8::kGCCallbackFlagForced;
+
     // FIXME: It would be nice if the GC callbacks passed the Isolate directly....
     v8::Isolate* isolate = v8::Isolate::GetCurrent();
     if (type == v8::kGCTypeScavenge) {
         minorGCEpilogue(isolate);
     } else if (type == v8::kGCTypeMarkSweepCompact) {
         majorGCEpilogue(isolate);
-        ThreadState::current()->didV8GC();
+        if (!forceGC)
+            ThreadState::current()->didV8MajorGC();
     }
 
-    // Forces a Blink heap garbage collection when a garbage collection
-    // was forced from V8. This is used for tests that force GCs from
-    // JavaScript to verify that objects die when expected.
-    if (flags & v8::kGCCallbackFlagForced) {
+    if (forceGC) {
         // This single GC is not enough for two reasons:
         //   (1) The GC is not precise because the GC scans on-stack pointers conservatively.
         //   (2) One GC is not enough to break a chain of persistent handles. It's possible that
         //       some heap allocated objects own objects that contain persistent handles
         //       pointing to other heap allocated objects. To break the chain, we need multiple GCs.
         //
         // Regarding (1), we force a precise GC at the end of the current event loop. So if you want
         // to collect all garbage, you need to wait until the next event loop.
         // Regarding (2), it would be OK in practice to trigger only one GC per gcEpilogue, because
         // GCController.collectAll() forces 7 V8's GC.
@@ skipping 89 matching lines @@
     Visitor* m_visitor;
 };
 
 void V8GCController::traceDOMWrappers(v8::Isolate* isolate, Visitor* visitor)
 {
     DOMWrapperTracer tracer(visitor);
     v8::V8::VisitHandlesWithClassIds(isolate, &tracer);
 }
 
 } // namespace blink