Reduce new space size when average scavenging time is high

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 37eb00485f7ae463aadeb41b3a5d3a6b4143a70b..c4cb7d4466f1d6211c54599f3a66ca791867db8a 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -738,8 +738,7 @@ void Heap::GarbageCollectionEpilogue() {
   new_space_top_after_last_gc_ = new_space()->top();
   last_gc_time_ = MonotonicallyIncreasingTimeInMs();
 
-  ReduceNewSpaceSize(
-      tracer()->CurrentAllocationThroughputInBytesPerMillisecond());
+  ReduceNewSpaceSize();
 }
 
 
@@ -1436,6 +1435,7 @@ static void VerifyNonPointerSpacePointers(Heap* heap) {
 
 
 void Heap::CheckNewSpaceExpansionCriteria() {
+  if (!HasLowYoungGenerationAllocationUtilization()) {
   if (FLAG_experimental_new_space_growth_heuristic) {
     if (new_space_.TotalCapacity() < new_space_.MaximumCapacity() &&
         survived_last_scavenge_ * 100 / new_space_.TotalCapacity() >= 10) {
@@ -1451,6 +1451,7 @@ void Heap::CheckNewSpaceExpansionCriteria() {
     new_space_.Grow();
     survived_since_last_expansion_ = 0;
   }
+  }
 }
 
 
@@ -4509,17 +4510,35 @@ void Heap::MakeHeapIterable() {
 }
 
 
-bool Heap::HasLowAllocationRate(size_t allocation_rate) {
+bool Heap::HasLowAllocationRate() {
   static const size_t kLowAllocationRate = 1000;
+  size_t allocation_rate =
+      tracer()->CurrentAllocationThroughputInBytesPerMillisecond();
   if (allocation_rate == 0) return false;
   return allocation_rate < kLowAllocationRate;
 }
 
 
-void Heap::ReduceNewSpaceSize(size_t allocation_rate) {
-  if (!FLAG_predictable && HasLowAllocationRate(allocation_rate)) {
-    new_space_.Shrink();
-    UncommitFromSpace();
+bool Heap::HasLowYoungGenerationAllocationUtilization() {
+  const double low_mutator_utilization = 0.01;
+  double allocation_speed = static_cast<double>(
+      tracer()->NewSpaceAllocationThroughputInBytesPerMillisecond());
+  double scavenging_speed =
+      static_cast<double>(tracer()->ScavengeSpeedInBytesPerMillisecond());
+  double mutator_utilization =
+      allocation_speed / (allocation_speed + scavenging_speed);
+  return mutator_utilization < low_mutator_utilization;
+}
+
+
+void Heap::ReduceNewSpaceSize() {
+  if (!FLAG_predictable) {
+    if (HasLowYoungGenerationAllocationUtilization()) {
+      new_space_.Shrink();
+    }
+    if (HasLowAllocationRate()) {
+      UncommitFromSpace();
+    }
   }
 }
 
@@ -4576,8 +4595,7 @@ GCIdleTimeHandler::HeapState Heap::ComputeHeapState() {
   heap_state.current_allocation_throughput_in_bytes_per_ms =
       tracer()->CurrentAllocationThroughputInBytesPerMillisecond();
   intptr_t limit = old_generation_allocation_limit_;
-  if (HasLowAllocationRate(
-          heap_state.current_allocation_throughput_in_bytes_per_ms)) {
+  if (HasLowAllocationRate()) {
     limit = idle_old_generation_allocation_limit_;
   }
   heap_state.can_start_incremental_marking =