Make sure that memory reducer makes progress in incremental marking

even if there are no idle notifications.

BUG=chromium:515873
LOG=NO

Review URL: https://codereview.chromium.org/1274633003

Cr-Commit-Position: refs/heads/master@{#30062}

src/heap/heap.cc

@@ -4778,6 +4778,19 @@ void Heap::ReduceNewSpaceSize() {
 }
 
 
+void Heap::FinalizeIncrementalMarkingIfComplete(const char* comment) {
+  if (FLAG_overapproximate_weak_closure &&
+      (incremental_marking()->IsReadyToOverApproximateWeakClosure() ||
+       (!incremental_marking()->weak_closure_was_overapproximated() &&
+        mark_compact_collector_.marking_deque()->IsEmpty()))) {
+    OverApproximateWeakClosure(comment);
+  } else if (incremental_marking()->IsComplete() ||
+             (mark_compact_collector_.marking_deque()->IsEmpty())) {
+    CollectAllGarbage(kNoGCFlags, comment);
+  }
+}
+
+
 bool Heap::TryFinalizeIdleIncrementalMarking(
     double idle_time_in_ms, size_t size_of_objects,
     size_t final_incremental_mark_compact_speed_in_bytes_per_ms) {

src/heap/heap.h

@@ -867,6 +867,8 @@ class Heap {
       intptr_t step_size_in_bytes, double deadline_in_ms,
       IncrementalMarking::StepActions step_actions);
 
+  void FinalizeIncrementalMarkingIfComplete(const char* comment);
+
   inline void increment_scan_on_scavenge_pages() {
     scan_on_scavenge_pages_++;
     if (FLAG_gc_verbose) {
@@ -1650,6 +1652,8 @@ class Heap {
   bool HasHighFragmentation();
   bool HasHighFragmentation(intptr_t used, intptr_t committed);
 
+  bool ShouldOptimizeForMemoryUsage() { return optimize_for_memory_usage_; }
+
  protected:
   // Methods made available to tests.
 

src/heap/memory-reducer.cc

@@ -45,12 +45,35 @@ void MemoryReducer::NotifyTimer(const Event& event) {
   if (state_.action == kRun) {
     DCHECK(heap()->incremental_marking()->IsStopped());
     DCHECK(FLAG_incremental_marking);
-    heap()->StartIdleIncrementalMarking();
     if (FLAG_trace_gc_verbose) {
       PrintIsolate(heap()->isolate(), "Memory reducer: started GC #%d\n",
                    state_.started_gcs);
     }
+    if (heap()->ShouldOptimizeForMemoryUsage()) {
+      // Do full GC if memory usage has higher priority than latency. This is
+      // important for background tabs that do not send idle notifications.
+      heap()->CollectAllGarbage(Heap::kReduceMemoryFootprintMask,
+                                "memory reducer");
+    } else {
+      heap()->StartIdleIncrementalMarking();
+    }
   } else if (state_.action == kWait) {
+    if (!heap()->incremental_marking()->IsStopped() &&
+        heap()->ShouldOptimizeForMemoryUsage()) {
+      // Make progress with pending incremental marking if memory usage has
+      // higher priority than latency. This is important for background tabs
+      // that do not send idle notifications.
+      const int kIncrementalMarkingDelayMs = 500;
+      double deadline = heap()->MonotonicallyIncreasingTimeInMs() +
+                        kIncrementalMarkingDelayMs;
+      heap()->AdvanceIncrementalMarking(
+          0, deadline, i::IncrementalMarking::StepActions(
+                           i::IncrementalMarking::NO_GC_VIA_STACK_GUARD,
+                           i::IncrementalMarking::FORCE_MARKING,
+                           i::IncrementalMarking::FORCE_COMPLETION));
+      heap()->FinalizeIncrementalMarkingIfComplete(
+          "Memory reducer: finalize incremental marking");
+    }
     // Re-schedule the timer.
     ScheduleTimer(state_.next_gc_start_ms - event.time_ms);
     if (FLAG_trace_gc_verbose) {