[heap] Convert overapproximate weak closure phase into finalize incremental marking phase and revis…

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/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/conversions.h"
 #include "src/heap/gc-idle-time-handler.h"
@@ skipping 24 matching lines @@
       bytes_rescanned_(0),
       should_hurry_(false),
       marking_speed_(0),
       bytes_scanned_(0),
       allocated_(0),
       write_barriers_invoked_since_last_step_(0),
       idle_marking_delay_counter_(0),
       no_marking_scope_depth_(0),
       unscanned_bytes_of_large_object_(0),
       was_activated_(false),
-      weak_closure_was_overapproximated_(false),
-      weak_closure_approximation_rounds_(0),
+      finalize_marking_completed_(false),
+      incremental_marking_finalization_rounds_(0),
       request_type_(COMPLETE_MARKING) {}
 
 
 bool IncrementalMarking::BaseRecordWrite(HeapObject* obj, Object** slot,
                                          Object* value) {
   HeapObject* value_heap_obj = HeapObject::cast(value);
   MarkBit value_bit = Marking::MarkBitFrom(value_heap_obj);
   if (Marking::IsWhite(value_bit)) {
     MarkBit obj_bit = Marking::MarkBitFrom(obj);
     if (Marking::IsBlack(obj_bit)) {
@@ skipping 559 matching lines @@
   IncrementalMarkingRootMarkingVisitor visitor(this);
   heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
 
   // Ready to start incremental marking.
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Running\n");
   }
 }
 
 
+void IncrementalMarking::MarkRoots() {
+  DCHECK(FLAG_finalize_marking_incrementally);
+  DCHECK(!finalize_marking_completed_);
+  DCHECK(IsMarking());
+
+  IncrementalMarkingRootMarkingVisitor visitor(this);
+  heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
+}
+
+
 void IncrementalMarking::MarkObjectGroups() {
-  DCHECK(FLAG_overapproximate_weak_closure);
-  DCHECK(!weak_closure_was_overapproximated_);
+  DCHECK(FLAG_finalize_marking_incrementally);
+  DCHECK(!finalize_marking_completed_);
+  DCHECK(IsMarking());
+
+  IncrementalMarkingRootMarkingVisitor visitor(this);
+  heap_->mark_compact_collector()->MarkImplicitRefGroups(&MarkObject);
+  heap_->isolate()->global_handles()->IterateObjectGroups(
+      &visitor, &MarkCompactCollector::IsUnmarkedHeapObjectWithHeap);
+  heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
+  heap_->isolate()->global_handles()->RemoveObjectGroups();
+}
+
+
+void IncrementalMarking::FinalizeIncrementally() {
+  DCHECK(FLAG_finalize_marking_incrementally);
+  DCHECK(!finalize_marking_completed_);
   DCHECK(IsMarking());
 
   int old_marking_deque_top =
       heap_->mark_compact_collector()->marking_deque()->top();
 
-  heap_->mark_compact_collector()->MarkImplicitRefGroups(&MarkObject);
-
-  IncrementalMarkingRootMarkingVisitor visitor(this);
-  heap_->isolate()->global_handles()->IterateObjectGroups(
-      &visitor, &MarkCompactCollector::IsUnmarkedHeapObjectWithHeap);
+  // After finishing incremental marking, we try to discover all unmarked
+  // objects to reduce the marking load in the final pause.
+  // 1) We scan and mark the roots again to find all changes to the root set.
+  // 2) We mark the object groups.
+  MarkRoots();
+  MarkObjectGroups();
 
   int marking_progress =
       abs(old_marking_deque_top -
-          heap_->mark_compact_collector()->marking_deque()->top());
+          heap_->mark_compact_collector()->marking_deque()->top()) /
+      kPointerSize;
 
-  ++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;
+  ++incremental_marking_finalization_rounds_;
+  if ((incremental_marking_finalization_rounds_ >=
+       FLAG_max_incremental_marking_finalization_rounds) ||
+      (marking_progress <
+       FLAG_min_progress_during_incremental_marking_finalization)) {
+    finalize_marking_completed_ = true;
   }
-
-  heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
-  heap_->isolate()->global_handles()->RemoveObjectGroups();
 }
 
 
 void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
   if (!IsMarking()) return;
 
   MarkingDeque* marking_deque =
       heap_->mark_compact_collector()->marking_deque();
   int current = marking_deque->bottom();
   int mask = marking_deque->mask();
@@ skipping 190 matching lines @@
   IncrementalMarking::set_should_hurry(false);
   ResetStepCounters();
   PatchIncrementalMarkingRecordWriteStubs(heap_,
                                           RecordWriteStub::STORE_BUFFER_ONLY);
   DeactivateIncrementalWriteBarrier();
   DCHECK(heap_->mark_compact_collector()->marking_deque()->IsEmpty());
   heap_->isolate()->stack_guard()->ClearGC();
 }
 
 
-void IncrementalMarking::OverApproximateWeakClosure(CompletionAction action) {
-  DCHECK(FLAG_overapproximate_weak_closure);
-  DCHECK(!weak_closure_was_overapproximated_);
+void IncrementalMarking::FinalizeMarking(CompletionAction action) {
+  DCHECK(FLAG_finalize_marking_incrementally);
+  DCHECK(!finalize_marking_completed_);
   if (FLAG_trace_incremental_marking) {
-    PrintF("[IncrementalMarking] requesting weak closure overapproximation.\n");
+    PrintF(
+        "[IncrementalMarking] requesting finalization of incremental "
+        "marking.\n");
   }
-  request_type_ = OVERAPPROXIMATION;
+  request_type_ = FINALIZATION;
   if (action == GC_VIA_STACK_GUARD) {
     heap_->isolate()->stack_guard()->RequestGC();
   }
 }
 
 
 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_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Complete (normal).\n");
   }
   request_type_ = COMPLETE_MARKING;
   if (action == GC_VIA_STACK_GUARD) {
     heap_->isolate()->stack_guard()->RequestGC();
   }
 }
 
 
 void IncrementalMarking::Epilogue() {
   was_activated_ = false;
-  weak_closure_was_overapproximated_ = false;
-  weak_closure_approximation_rounds_ = 0;
+  finalize_marking_completed_ = false;
+  incremental_marking_finalization_rounds_ = 0;
 }
 
 
 double IncrementalMarking::AdvanceIncrementalMarking(
     intptr_t step_size_in_bytes, double deadline_in_ms,
     IncrementalMarking::StepActions step_actions) {
   DCHECK(!IsStopped());
 
   if (step_size_in_bytes == 0) {
     step_size_in_bytes = GCIdleTimeHandler::EstimateMarkingStepSize(
@@ skipping 157 matching lines @@
       }
       if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
         bytes_scanned_ = 0;
         StartMarking();
       }
     } else if (state_ == MARKING) {
       bytes_processed = ProcessMarkingDeque(bytes_to_process);
       if (heap_->mark_compact_collector()->marking_deque()->IsEmpty()) {
         if (completion == FORCE_COMPLETION ||
             IsIdleMarkingDelayCounterLimitReached()) {
-          if (FLAG_overapproximate_weak_closure &&
-              !weak_closure_was_overapproximated_) {
-            OverApproximateWeakClosure(action);
+          if (FLAG_finalize_marking_incrementally &&
+              !finalize_marking_completed_) {
+            FinalizeMarking(action);
           } else {
             MarkingComplete(action);
           }
         } else {
           IncrementIdleMarkingDelayCounter();
         }
       }
     }
 
     steps_count_++;
@@ skipping 39 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }  // namespace internal
 }  // namespace v8