[heap] no longer perform GC to make heap iterable.

src/heap/heap.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/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/context-slot-cache.h"
 #include "src/base/bits.h"
@@ skipping 4049 matching lines @@
   Struct* result = nullptr;
   {
     AllocationResult allocation = Allocate(map, OLD_SPACE);
     if (!allocation.To(&result)) return allocation;
   }
   result->InitializeBody(size);
   return result;
 }
 
 
-bool Heap::IsHeapIterable() {
-  // TODO(hpayer): This function is not correct. Allocation folding in old
-  // space breaks the iterability.
-  return new_space_top_after_last_gc_ == new_space()->top();
-}
-
-
 void Heap::MakeHeapIterable() {

[Hannes Payer (out of office), 2017/02/10 07:37:18]

FYI: We do not need to wait for sweepers to make the heap iterable. However, it
is easier to do that to avoid races with the sweeper while iterating.

-  DCHECK(AllowHeapAllocation::IsAllowed());
-  if (!IsHeapIterable()) {
-    CollectAllGarbage(kMakeHeapIterableMask,
-                      GarbageCollectionReason::kMakeHeapIterable);
-  }
   mark_compact_collector()->EnsureSweepingCompleted();
-  DCHECK(IsHeapIterable());
 }
 
 
 static double ComputeMutatorUtilization(double mutator_speed, double gc_speed) {
   const double kMinMutatorUtilization = 0.0;
   const double kConservativeGcSpeedInBytesPerMillisecond = 200000;
   if (mutator_speed == 0) return kMinMutatorUtilization;
   if (gc_speed == 0) gc_speed = kConservativeGcSpeedInBytesPerMillisecond;
   // Derivation:
   // mutator_utilization = mutator_time / (mutator_time + gc_time)
@@ skipping 2015 matching lines @@
   void MarkReachableObjects() {
     MarkingVisitor visitor;
     heap_->IterateRoots(&visitor, VISIT_ALL);
     visitor.TransitiveClosure();
   }
 
   Heap* heap_;
   DisallowHeapAllocation no_allocation_;
 };
 
-
 HeapIterator::HeapIterator(Heap* heap,
                            HeapIterator::HeapObjectsFiltering filtering)
-    : make_heap_iterable_helper_(heap),
-      no_heap_allocation_(),
+    : no_heap_allocation_(),
       heap_(heap),
       filtering_(filtering),
       filter_(nullptr),
       space_iterator_(nullptr),
       object_iterator_(nullptr) {
+  heap_->MakeHeapIterable();
   heap_->heap_iterator_start();
   // Start the iteration.
   space_iterator_ = new SpaceIterator(heap_);
   switch (filtering_) {
     case kFilterUnreachable:
       filter_ = new UnreachableObjectsFilter(heap_);
       break;
     default:
       break;
   }
@@ skipping 413 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8