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

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

 // Copyright 2014 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.
 
 #ifndef V8_HEAP_GC_IDLE_TIME_HANDLER_H_
 #define V8_HEAP_GC_IDLE_TIME_HANDLER_H_
 
 #include "src/globals.h"
 
 namespace v8 {
@@ skipping 31 matching lines @@
     GCIdleTimeAction result;
     result.type = DO_FULL_GC;
     result.parameter = 0;
     return result;
   }
 
   GCIdleTimeActionType type;
   intptr_t parameter;
 };
 
+
 class GCTracer;
 
 // The idle time handler makes decisions about which garbage collection
 // operations are executing during IdleNotification.
 class GCIdleTimeHandler {
  public:
   // If we haven't recorded any incremental marking events yet, we carefully
   // mark with a conservative lower bound for the marking speed.
   static const size_t kInitialConservativeMarkingSpeed = 100 * KB;
 
   // Maximum marking step size returned by EstimateMarkingStepSize.
   static const size_t kMaximumMarkingStepSize = 700 * MB;
 
   // We have to make sure that we finish the IdleNotification before
   // idle_time_in_ms. Hence, we conservatively prune our workload estimate.
   static const double kConservativeTimeRatio;
 
   // If we haven't recorded any mark-compact events yet, we use
   // conservative lower bound for the mark-compact speed.
   static const size_t kInitialConservativeMarkCompactSpeed = 2 * MB;
 
   // Maximum mark-compact time returned by EstimateMarkCompactTime.
   static const size_t kMaxMarkCompactTimeInMs;
 
+  struct HeapState {
+    int contexts_disposed;
+    size_t size_of_objects;
+    bool incremental_marking_stopped;
+    bool can_start_incremental_marking;
+  };
+
   GCIdleTimeHandler()
       : mark_compacts_since_idle_round_started_(0),
         scavenges_since_last_idle_round_(0) {}
 
-  GCIdleTimeAction Compute(int idle_time_in_ms, int contexts_disposed,
-                           size_t size_of_objects,
-                           bool incremental_marking_stopped,
+  GCIdleTimeAction Compute(int idle_time_in_ms, HeapState heap_state,
                            GCTracer* gc_tracer);
 
   void NotifyIdleMarkCompact() {
     if (mark_compacts_since_idle_round_started_ < kMaxMarkCompactsInIdleRound) {
       ++mark_compacts_since_idle_round_started_;
       if (mark_compacts_since_idle_round_started_ ==
           kMaxMarkCompactsInIdleRound) {
         scavenges_since_last_idle_round_ = 0;
       }
     }
@@ skipping 22 matching lines @@
   int mark_compacts_since_idle_round_started_;
   int scavenges_since_last_idle_round_;
 
   DISALLOW_COPY_AND_ASSIGN(GCIdleTimeHandler);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_GC_IDLE_TIME_HANDLER_H_