Start incremental marking in idle time handler only if it is worthwhile.

src/heap/heap.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/accessors.h"
 #include "src/api.h"
 #include "src/base/once.h"
 #include "src/base/utils/random-number-generator.h"
@@ skipping 828 matching lines @@
     }
 
     GarbageCollectionEpilogue();
     tracer()->Stop();
   }
 
   // Start incremental marking for the next cycle. The heap snapshot
   // generator needs incremental marking to stay off after it aborted.
   if (!mark_compact_collector()->abort_incremental_marking() &&
       incremental_marking()->IsStopped() &&
-      incremental_marking()->WorthActivating() && NextGCIsLikelyToBeFull()) {
+      WorthActivatingIncrementalMarking()) {
     incremental_marking()->Start();
   }
 
   return next_gc_likely_to_collect_more;
 }
 
 
 int Heap::NotifyContextDisposed() {
   if (isolate()->concurrent_recompilation_enabled()) {
     // Flush the queued recompilation tasks.
@@ skipping 3416 matching lines @@
     gc_idle_time_handler_.NotifyIdleMarkCompact();
     gc_count_at_last_idle_gc_ = gc_count_;
     if (uncommit) {
       new_space_.Shrink();
       UncommitFromSpace();
     }
   }
 }
 
 
+bool Heap::WorthActivatingIncrementalMarking() {
+  return incremental_marking()->WorthActivating() && NextGCIsLikelyToBeFull();
+}
+
+
 bool Heap::IdleNotification(int idle_time_in_ms) {
   // If incremental marking is off, we do not perform idle notification.
   if (!FLAG_incremental_marking) return true;
   isolate()->counters()->gc_idle_time_allotted_in_ms()->AddSample(
       idle_time_in_ms);
   HistogramTimerScope idle_notification_scope(
       isolate_->counters()->gc_idle_notification());
 
   GCIdleTimeAction action = gc_idle_time_handler_.Compute(
       idle_time_in_ms, contexts_disposed_, static_cast<size_t>(SizeOfObjects()),
       incremental_marking()->IsStopped(), tracer());
   contexts_disposed_ = 0;
   bool result = false;
   switch (action.type) {
     case DO_INCREMENTAL_MARKING:
-      if (incremental_marking()->IsStopped()) {
+      if (incremental_marking()->IsStopped() &&
+          WorthActivatingIncrementalMarking()) {

[Hannes Payer (out of office), 2014/08/21 15:25:18]

As discussed offline, can we move that into GCIdleTimeHandler Compute?

         incremental_marking()->Start();
       }
       AdvanceIdleIncrementalMarking(action.parameter);
       break;
     case DO_FULL_GC: {
       HistogramTimerScope scope(isolate_->counters()->gc_context());
       const char* message = contexts_disposed_
                                 ? "idle notification: contexts disposed"
                                 : "idle notification: finalize idle round";
       CollectAllGarbage(kReduceMemoryFootprintMask, message);
@@ skipping 1788 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 }
 }  // namespace v8::internal