Add a flag to over approximate the weak closure during GC

src/heap/incremental-marking.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 10 matching lines @@
       state_(STOPPED),
       steps_count_(0),
       old_generation_space_available_at_start_of_incremental_(0),
       old_generation_space_used_at_start_of_incremental_(0),
       should_hurry_(false),
       marking_speed_(0),
       allocated_(0),
       idle_marking_delay_counter_(0),
       no_marking_scope_depth_(0),
       unscanned_bytes_of_large_object_(0),
-      was_activated_(false) {}
+      was_activated_(false),
+      weak_closure_was_overapproximated_(false) {}
 
 
 void IncrementalMarking::RecordWriteSlow(HeapObject* obj, Object** slot,
                                          Object* value) {
   if (BaseRecordWrite(obj, slot, value) && slot != NULL) {
     MarkBit obj_bit = Marking::MarkBitFrom(obj);
     if (Marking::IsBlack(obj_bit)) {
       // Object is not going to be rescanned we need to record the slot.
       heap_->mark_compact_collector()->RecordSlot(HeapObject::RawField(obj, 0),
                                                   slot, value);
@@ skipping 446 matching lines @@
   }
   DCHECK(FLAG_incremental_marking);
   DCHECK(FLAG_incremental_marking_steps);
   DCHECK(state_ == STOPPED);
   DCHECK(heap_->gc_state() == Heap::NOT_IN_GC);
   DCHECK(!heap_->isolate()->serializer_enabled());
 
   ResetStepCounters();
 
   was_activated_ = true;
+  weak_closure_was_overapproximated_ = false;

[Hannes Payer (out of office), 2015/02/03 17:40:11]

Can we do that in the gc epilogue?

[jochen (gone - plz use gerrit), 2015/02/09 16:03:43]

Done

 
   if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
     StartMarking(flag);
   } else {
     if (FLAG_trace_incremental_marking) {
       PrintF("[IncrementalMarking] Start sweeping.\n");
     }
     state_ = SWEEPING;
   }
 
@@ skipping 257 matching lines @@
   ResetStepCounters();
   PatchIncrementalMarkingRecordWriteStubs(heap_,
                                           RecordWriteStub::STORE_BUFFER_ONLY);
   DeactivateIncrementalWriteBarrier();
   DCHECK(heap_->mark_compact_collector()->marking_deque()->IsEmpty());
   heap_->isolate()->stack_guard()->ClearGC();
 }
 
 
 void IncrementalMarking::MarkingComplete(CompletionAction action) {
-  state_ = COMPLETE;
   // We will set the stack guard to request a GC now.  This will mean the rest
   // of the GC gets performed as soon as possible (we can't do a GC here in a
   // record-write context).  If a few things get allocated between now and then
   // that shouldn't make us do a scavenge and keep being incremental, so we set
   // the should-hurry flag to indicate that there can't be much work left to do.
   set_should_hurry(true);
+  if (FLAG_overapproximate_weak_closure &&
+      !weak_closure_was_overapproximated_ && action == GC_VIA_STACK_GUARD) {
+    if (FLAG_trace_incremental_marking) {

[Hannes Payer (out of office), 2015/02/03 17:40:11]

Can we add a separate method for that and dispatch between over approximate and
dispatch at the call site?

[jochen (gone - plz use gerrit), 2015/02/09 16:03:43]

done

[jochen (gone - plz use gerrit), 2015/02/09 16:03:43]

done

+      PrintF(
+          "[IncrementalMarking] requesting weak closure overapproximation.\n");
+    }
+    heap_->isolate()->stack_guard()->RequestGC();
+    return;
+  }
+  state_ = COMPLETE;
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Complete (normal).\n");
   }
   if (action == GC_VIA_STACK_GUARD) {
     heap_->isolate()->stack_guard()->RequestGC();
   }
 }
 
 
 void IncrementalMarking::Epilogue() { was_activated_ = false; }
@@ skipping 189 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }
 }  // namespace v8::internal