When allocation rate is low and we are close to the new space limit, we should...

When allocation rate is low and we are close to the new space limit, we should perform a scavenge during idle time.

BUG=chromium:517395
LOG=n

Review URL: https://codereview.chromium.org/1272573006

Cr-Commit-Position: refs/heads/master@{#30044}

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

@@ -129,10 +129,7 @@ bool GCIdleTimeHandler::ShouldDoScavenge(
 
   // We do not know the allocation throughput before the first scavenge.
   // TODO(hpayer): Estimate allocation throughput before the first scavenge.
-  if (new_space_allocation_throughput_in_bytes_per_ms == 0) {
-    new_space_allocation_limit =
-        static_cast<size_t>(new_space_size * kConservativeTimeRatio);
-  } else {
+  if (new_space_allocation_throughput_in_bytes_per_ms > 0) {
     // We have to trigger scavenge before we reach the end of new space.
     size_t adjust_limit = new_space_allocation_throughput_in_bytes_per_ms *
                           kTimeUntilNextIdleEvent;
@@ -143,6 +140,13 @@ bool GCIdleTimeHandler::ShouldDoScavenge(
     }
   }
 
+  if (new_space_allocation_throughput_in_bytes_per_ms <
+      kLowAllocationThroughput) {
+    new_space_allocation_limit =
+        Min(new_space_allocation_limit,
+            static_cast<size_t>(new_space_size * kConservativeTimeRatio));
+  }
+
   // The allocated new space limit to trigger a scavange has to be at least
   // kMinimumNewSpaceSizeToPerformScavenge.
   if (new_space_allocation_limit < kMinimumNewSpaceSizeToPerformScavenge) {

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

@@ -124,6 +124,10 @@ class GCIdleTimeHandler {
   // no idle notification happens.
   static const size_t kTimeUntilNextIdleEvent = 100;
 
+  // An allocation throughput below kLowAllocationThroughput bytes/ms is
+  // considered low
+  static const size_t kLowAllocationThroughput = 1000;
+
   // If we haven't recorded any scavenger events yet, we use a conservative
   // lower bound for the scavenger speed.
   static const size_t kInitialConservativeScavengeSpeed = 100 * KB;

test/unittests/heap/gc-idle-time-handler-unittest.cc

@@ -156,6 +156,19 @@ TEST_F(GCIdleTimeHandlerTest, DoScavengeLowScavengeSpeed) {
 }
 
 
+TEST_F(GCIdleTimeHandlerTest, DoScavengeLowAllocationRate) {
+  GCIdleTimeHandler::HeapState heap_state = DefaultHeapState();
+  heap_state.used_new_space_size = kNewSpaceCapacity;
+  heap_state.new_space_allocation_throughput_in_bytes_per_ms =
+      GCIdleTimeHandler::kLowAllocationThroughput - 1;
+  int idle_time_ms = 16;
+  EXPECT_TRUE(GCIdleTimeHandler::ShouldDoScavenge(
+      idle_time_ms, heap_state.new_space_capacity,
+      heap_state.used_new_space_size, heap_state.scavenge_speed_in_bytes_per_ms,
+      heap_state.new_space_allocation_throughput_in_bytes_per_ms));
+}
+
+
 TEST_F(GCIdleTimeHandlerTest, DoScavengeHighScavengeSpeed) {
   GCIdleTimeHandler::HeapState heap_state = DefaultHeapState();
   heap_state.used_new_space_size = kNewSpaceCapacity;