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

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 5a10a5cd210ac4da9700d1a746410fc787f93c6c..ac8ceef4101da5b65a65a9667dd08657833b1a62 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -4565,8 +4565,16 @@ void Heap::MakeHeapIterable() {
 }
 
 
-void Heap::ReduceNewSpaceSize(GCIdleTimeAction action) {
-  if (action.reduce_memory &&
+bool Heap::HasLowAllocationRate(GCIdleTimeHandler::HeapState heap_state) {
+  static const size_t kLowAllocationRate = 1000;
+  return heap_state.current_new_space_allocation_throughput_in_bytes_per_ms <

[ulan, 2015/05/21 15:21:25]

check for heap_state.current_new_space_allocation_throughput_in_bytes_per_ms ==
0 and be conservative in that case?

[Hannes Payer (out of office), 2015/05/21 17:17:03]

Good point! Done.

+         kLowAllocationRate;
+}
+
+
+void Heap::ReduceNewSpaceSize(GCIdleTimeAction action,
+                              GCIdleTimeHandler::HeapState heap_state) {
+  if (HasLowAllocationRate(heap_state) &&
       (action.type == DO_SCAVENGE || action.type == DO_FULL_GC ||
        (action.type == DO_INCREMENTAL_MARKING &&
         incremental_marking()->IsStopped()))) {
@@ -4635,6 +4643,8 @@ GCIdleTimeHandler::HeapState Heap::ComputeHeapState(bool reduce_memory) {
   heap_state.new_space_capacity = new_space_.Capacity();
   heap_state.new_space_allocation_throughput_in_bytes_per_ms =
       tracer()->NewSpaceAllocationThroughputInBytesPerMillisecond();
+  heap_state.current_new_space_allocation_throughput_in_bytes_per_ms =
+      tracer()->CurrentNewSpaceAllocationThroughputInBytesPerMillisecond();
   return heap_state;
 }
 
@@ -4697,7 +4707,7 @@ bool Heap::PerformIdleTimeAction(GCIdleTimeAction action,
       break;
   }
 
-  ReduceNewSpaceSize(action);
+  ReduceNewSpaceSize(action, heap_state);
   return result;
 }