Reduce context disposal gc overhead.

BUG=

Review URL: https://codereview.chromium.org/750963002

Cr-Commit-Position: refs/heads/master@{#25494}

src/heap/gc-idle-time-handler.cc

@@ -142,6 +142,13 @@ bool GCIdleTimeHandler::ShouldDoMarkCompact(
 }
 
 
+bool GCIdleTimeHandler::ShouldDoContextDisposalMarkCompact(
+    bool context_disposed, double contexts_disposal_rate) {
+  return context_disposed && contexts_disposal_rate > 0 &&
+         contexts_disposal_rate < kHighContextDisposalRate;
+}
+
+
 // The following logic is implemented by the controller:
 // (1) If we don't have any idle time, do nothing, unless a context was
 // disposed, incremental marking is stopped, and the heap is small. Then do
@@ -163,8 +170,9 @@ GCIdleTimeAction GCIdleTimeHandler::Compute(size_t idle_time_in_ms,
                                             HeapState heap_state) {
   if (idle_time_in_ms == 0) {
     if (heap_state.incremental_marking_stopped) {
-      if (heap_state.contexts_disposed > 0 &&
-          heap_state.contexts_disposal_rate < kHighContextDisposalRate) {
+      if (ShouldDoContextDisposalMarkCompact(
+              heap_state.contexts_disposed,
+              heap_state.contexts_disposal_rate)) {
         return GCIdleTimeAction::FullGC();
       }
     }

src/heap/gc-idle-time-handler.h

@@ -162,6 +162,9 @@ class GCIdleTimeHandler {
                                   size_t size_of_objects,
                                   size_t mark_compact_speed_in_bytes_per_ms);
 
+  static bool ShouldDoContextDisposalMarkCompact(bool context_disposed,
+                                                 double contexts_disposal_rate);
+
   static bool ShouldDoScavenge(
       size_t idle_time_in_ms, size_t new_space_size, size_t used_new_space_size,
       size_t scavenger_speed_in_bytes_per_ms,

src/heap/gc-tracer.cc

@@ -490,7 +490,7 @@ intptr_t GCTracer::NewSpaceAllocationThroughputInBytesPerMillisecond() const {
 
 
 double GCTracer::ContextDisposalRateInMilliseconds() const {
-  if (context_disposal_events_.size() == 0) return 0.0;
+  if (context_disposal_events_.size() < kRingBufferMaxSize) return 0.0;
 
   double begin = base::OS::TimeCurrentMillis();
   double end = 0.0;

src/heap/gc-tracer.h

@@ -248,7 +248,7 @@ class GCTracer {
     double scopes[Scope::NUMBER_OF_SCOPES];
   };
 
-  static const int kRingBufferMaxSize = 10;
+  static const size_t kRingBufferMaxSize = 10;
 
   typedef RingBuffer<Event, kRingBufferMaxSize> EventBuffer;
 

src/heap/heap.cc

@@ -4451,8 +4451,7 @@ bool Heap::IdleNotification(int idle_time_in_ms) {
     case DO_FULL_GC: {
       HistogramTimerScope scope(isolate_->counters()->gc_context());
       if (contexts_disposed_) {
-        CollectAllGarbage(kReduceMemoryFootprintMask,
-                          "idle notification: contexts disposed");
+        CollectAllGarbage(kNoGCFlags, "idle notification: contexts disposed");
         gc_idle_time_handler_.NotifyIdleMarkCompact();
         gc_count_at_last_idle_gc_ = gc_count_;
       } else {