Repeatedly overapproximate the weak closure as long as we make progress

src/heap/incremental-marking.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 527 matching lines @@
   IncrementalMarkingRootMarkingVisitor visitor(this);
   heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
 
   // Ready to start incremental marking.
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Running\n");
   }
 }
 
 
 void IncrementalMarking::MarkObjectGroups() {

[Hannes Payer (out of office), 2015/03/16 12:09:24]

Should we have an upper bound on of how often this function is executing in one
overapproximation round?

   DCHECK(FLAG_overapproximate_weak_closure);
   DCHECK(!weak_closure_was_overapproximated_);
 
-  GCTracer::Scope gc_scope(heap_->tracer(),
-                           GCTracer::Scope::MC_INCREMENTAL_WEAKCLOSURE);
+  int old_marking_deque_top =
+      heap_->mark_compact_collector()->marking_deque()->top();
 
   heap_->mark_compact_collector()->MarkImplicitRefGroups(&MarkObject);
 
   IncrementalMarkingRootMarkingVisitor visitor(this);
   heap_->isolate()->global_handles()->IterateObjectGroups(
       &visitor, &MarkCompactCollector::IsUnmarkedHeapObjectWithHeap);
 
+  int marking_progress =
+      abs(old_marking_deque_top -
+          heap_->mark_compact_collector()->marking_deque()->top());
+
+  if (marking_progress < FLAG_min_progress_during_object_groups_marking) {
+    weak_closure_was_overapproximated_ = true;
+  }
+
   heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
   heap_->isolate()->global_handles()->RemoveObjectGroups();
-
-  weak_closure_was_overapproximated_ = true;
 }
 
 
 void IncrementalMarking::PrepareForScavenge() {
   if (!IsMarking()) return;
   NewSpacePageIterator it(heap_->new_space()->FromSpaceStart(),
                           heap_->new_space()->FromSpaceEnd());
   while (it.has_next()) {
     Bitmap::Clear(it.next());
   }
@@ skipping 443 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }
 }  // namespace v8::internal