Uncommit and shrink semi-spaces only on low allocation rate.

src/heap/gc-tracer.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_TRACER_H_
 #define V8_HEAP_GC_TRACER_H_
 
 #include "src/base/platform/platform.h"
 
 namespace v8 {
@@ skipping 371 matching lines @@
   intptr_t FinalIncrementalMarkCompactSpeedInBytesPerMillisecond() const;
 
   // Allocation throughput in the new space in bytes/millisecond.
   // Returns 0 if no allocation events have been recorded.
   size_t NewSpaceAllocationThroughputInBytesPerMillisecond() const;
 
   // Bytes allocated in new space in the specified time.
   // Returns 0 if no allocation events have been recorded.
   size_t NewSpaceAllocatedBytesInLast(double time_ms) const;
 
+  // Allocation throughput in the new space in bytes/milliseconds in
+  // the last five seconds.
+  // Returns 0 if no allocation events have been recorded.
+  size_t CurrentNewSpaceAllocationThroughputInBytesPerMillisecond() const;
+
   // Computes the context disposal rate in milliseconds. It takes the time
   // frame of the first recorded context disposal to the current time and
   // divides it by the number of recorded events.
   // Returns 0 if no events have been recorded.
   double ContextDisposalRateInMilliseconds() const;
 
   // Computes the average survival ratio based on the last recorded survival
   // events.
   // Returns 0 if no events have been recorded.
   double AverageSurvivalRatio() const;
@@ skipping 100 matching lines @@
 
   // Counts how many tracers were started without stopping.
   int start_counter_;
 
   DISALLOW_COPY_AND_ASSIGN(GCTracer);
 };
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_GC_TRACER_H_