[heap] Account potentially marked bytes collected by Scavenger.

We have a heuristics that allows the main thread to skip marking work
by the amount marked by the background tasks.
Scavenges that happen during incremental marking can reclaim marked
objects, which should be accounted in the main thread marking schedule.

Bug: chromium:789530
Change-Id: I9b922e05202e3b7665ec191c4fe303dbe7f72a50
Reviewed-on: https://chromium-review.googlesource.com/840843
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50285}

src/heap/heap.cc

@@ -1572,7 +1572,7 @@ bool Heap::PerformGarbageCollection(
 
   EnsureFromSpaceIsCommitted();
 
-  int start_new_space_size = static_cast<int>(Heap::new_space()->Size());
+  size_t start_new_space_size = Heap::new_space()->Size();
 
   {
     Heap::SkipStoreBufferScope skip_store_buffer_scope(store_buffer_);
@@ -1611,9 +1611,16 @@ bool Heap::PerformGarbageCollection(
     ProcessPretenuringFeedback();
   }
 
-  UpdateSurvivalStatistics(start_new_space_size);
+  UpdateSurvivalStatistics(static_cast<int>(start_new_space_size));
   ConfigureInitialOldGenerationSize();
 
+  if (collector != MARK_COMPACTOR) {
+    // Objects that died in the new space might have been accounted
+    // as bytes marked ahead of schedule by the incremental marker.
+    incremental_marking()->UpdateMarkedBytesAfterScavenge(
+        start_new_space_size - SurvivedNewSpaceObjectSize());
+  }
+
   if (!fast_promotion_mode_ || collector == MARK_COMPACTOR) {
     ComputeFastPromotionMode(promotion_ratio_ + semi_space_copied_rate_);
   }

src/heap/incremental-marking.cc

@@ -638,6 +638,13 @@ void IncrementalMarking::UpdateMarkingWorklistAfterScavenge() {
   });
 }
 
+void IncrementalMarking::UpdateMarkedBytesAfterScavenge(
+    size_t dead_bytes_in_new_space) {
+  if (!IsMarking()) return;
+  bytes_marked_ahead_of_schedule_ -=
+      Min(bytes_marked_ahead_of_schedule_, dead_bytes_in_new_space);
+}
+
 bool IncrementalMarking::IsFixedArrayWithProgressBar(HeapObject* obj) {
   if (!obj->IsFixedArray()) return false;
   MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());

src/heap/incremental-marking.h

@@ -165,6 +165,7 @@ class V8_EXPORT_PRIVATE IncrementalMarking {
   void FinalizeIncrementally();
 
   void UpdateMarkingWorklistAfterScavenge();
+  void UpdateMarkedBytesAfterScavenge(size_t dead_bytes_in_new_space);
 
   void Hurry();