Repeatedly overapproximate the weak closure as long as we make progress

Also, include the time for building object groups in the tracing scope
for the overapproximation.

BUG=v8:3862
R=hpayer@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/1012593004

Cr-Commit-Position: refs/heads/master@{#27218}

src/flag-definitions.h

@@ -613,6 +613,11 @@ DEFINE_BOOL(incremental_marking, true, "use incremental marking")
 DEFINE_BOOL(incremental_marking_steps, true, "do incremental marking steps")
 DEFINE_BOOL(overapproximate_weak_closure, false,
             "overapproximate weak closer to reduce atomic pause time")
+DEFINE_INT(min_progress_during_object_groups_marking, 128,
+           "keep overapproximating the weak closure as long as we discover at "
+           "least this many unmarked objects")
+DEFINE_INT(max_object_groups_marking_rounds, 3,
+           "at most try this many times to over approximate the weak closure")
 DEFINE_BOOL(concurrent_sweeping, true, "use concurrent sweeping")
 DEFINE_BOOL(trace_incremental_marking, false,
             "trace progress of the incremental marking")

src/heap/heap.cc

@@ -766,6 +766,10 @@ void Heap::OverApproximateWeakClosure(const char* gc_reason) {
     PrintF("[IncrementalMarking] Overapproximate weak closure (%s).\n",
            gc_reason);
   }
+
+  GCTracer::Scope gc_scope(tracer(),
+                           GCTracer::Scope::MC_INCREMENTAL_WEAKCLOSURE);
+
   {
     GCCallbacksScope scope(this);
     if (scope.CheckReenter()) {

src/heap/incremental-marking.cc

@@ -30,6 +30,7 @@ IncrementalMarking::IncrementalMarking(Heap* heap)
       unscanned_bytes_of_large_object_(0),
       was_activated_(false),
       weak_closure_was_overapproximated_(false),
+      weak_closure_approximation_rounds_(0),
       request_type_(COMPLETE_MARKING) {}
 
 
@@ -549,8 +550,8 @@ void IncrementalMarking::MarkObjectGroups() {
   DCHECK(FLAG_overapproximate_weak_closure);
   DCHECK(!weak_closure_was_overapproximated_);
 
-  GCTracer::Scope gc_scope(heap_->tracer(),
-                           GCTracer::Scope::MC_INCREMENTAL_WEAKCLOSURE);
+  int old_marking_deque_top =
+      heap_->mark_compact_collector()->marking_deque()->top();
 
   heap_->mark_compact_collector()->MarkImplicitRefGroups(&MarkObject);
 
@@ -558,10 +559,19 @@ void IncrementalMarking::MarkObjectGroups() {
   heap_->isolate()->global_handles()->IterateObjectGroups(
       &visitor, &MarkCompactCollector::IsUnmarkedHeapObjectWithHeap);
 
+  int marking_progress =
+      abs(old_marking_deque_top -
+          heap_->mark_compact_collector()->marking_deque()->top());
+
+  ++weak_closure_approximation_rounds_;
+  if ((weak_closure_approximation_rounds_ >=
+       FLAG_max_object_groups_marking_rounds) ||
+      (marking_progress < FLAG_min_progress_during_object_groups_marking)) {
+    weak_closure_was_overapproximated_ = true;
+  }
+
   heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
   heap_->isolate()->global_handles()->RemoveObjectGroups();
-
-  weak_closure_was_overapproximated_ = true;
 }
 
 
@@ -819,6 +829,7 @@ void IncrementalMarking::MarkingComplete(CompletionAction action) {
 void IncrementalMarking::Epilogue() {
   was_activated_ = false;
   weak_closure_was_overapproximated_ = false;
+  weak_closure_approximation_rounds_ = 0;
 }
 
 

src/heap/incremental-marking.h

@@ -41,9 +41,6 @@ class IncrementalMarking {
   bool weak_closure_was_overapproximated() const {
     return weak_closure_was_overapproximated_;
   }
-  void set_weak_closure_was_overapproximated(bool val) {
-    weak_closure_was_overapproximated_ = val;
-  }
 
   inline bool IsStopped() { return state() == STOPPED; }
 
@@ -249,6 +246,8 @@ class IncrementalMarking {
 
   bool weak_closure_was_overapproximated_;
 
+  int weak_closure_approximation_rounds_;
+
   GCRequestType request_type_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(IncrementalMarking);