[heap] Untangle parallel and concurrent marking flag

Callers of the ConcurrentMarking API should check the flags, which they were
already mostly doing.

Change-Id: Ie273bb740fe6d2b36dfb924ce813670ebd47bf3f
Reviewed-on: https://chromium-review.googlesource.com/c/1280307Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56638}

src/flag-definitions.h

@@ -736,7 +736,6 @@ DEFINE_BOOL(write_protect_code_memory, V8_WRITE_PROTECT_CODE_MEMORY_BOOL,
 DEFINE_BOOL(concurrent_marking, V8_CONCURRENT_MARKING_BOOL,
             "use concurrent marking")
 DEFINE_BOOL(parallel_marking, true, "use parallel marking in atomic pause")
-DEFINE_IMPLICATION(parallel_marking, concurrent_marking)
 DEFINE_INT(ephemeron_fixpoint_iterations, 10,
            "number of fixpoint iterations it takes to switch to linear "
            "ephemeron algorithm")

src/heap/concurrent-marking.cc

@@ -565,7 +565,7 @@ ConcurrentMarking::ConcurrentMarking(Heap* heap, MarkingWorklist* shared,
       embedder_objects_(embedder_objects) {
 // The runtime flag should be set only if the compile time flag was set.
 #ifndef V8_CONCURRENT_MARKING
-  CHECK(!FLAG_concurrent_marking);
+  CHECK(!FLAG_concurrent_marking && !FLAG_parallel_marking);
 #endif
 }
 
@@ -674,8 +674,8 @@ void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
 }
 
 void ConcurrentMarking::ScheduleTasks() {
+  DCHECK(FLAG_parallel_marking || FLAG_concurrent_marking);
   DCHECK(!heap_->IsTearingDown());
-  if (!FLAG_concurrent_marking) return;
   base::MutexGuard guard(&pending_lock_);
   DCHECK_EQ(0, pending_task_count_);
   if (task_count_ == 0) {
@@ -713,7 +713,8 @@ void ConcurrentMarking::ScheduleTasks() {
 }
 
 void ConcurrentMarking::RescheduleTasksIfNeeded() {
-  if (!FLAG_concurrent_marking || heap_->IsTearingDown()) return;
+  DCHECK(FLAG_parallel_marking || FLAG_concurrent_marking);
+  if (heap_->IsTearingDown()) return;
   {
     base::MutexGuard guard(&pending_lock_);
     if (pending_task_count_ > 0) return;
@@ -726,7 +727,7 @@ void ConcurrentMarking::RescheduleTasksIfNeeded() {
 }
 
 bool ConcurrentMarking::Stop(StopRequest stop_request) {
-  if (!FLAG_concurrent_marking) return false;
+  DCHECK(FLAG_parallel_marking || FLAG_concurrent_marking);
   base::MutexGuard guard(&pending_lock_);
 
   if (pending_task_count_ == 0) return false;
@@ -800,7 +801,8 @@ size_t ConcurrentMarking::TotalMarkedBytes() {
 
 ConcurrentMarking::PauseScope::PauseScope(ConcurrentMarking* concurrent_marking)
     : concurrent_marking_(concurrent_marking),
-      resume_on_exit_(concurrent_marking_->Stop(
+      resume_on_exit_(FLAG_concurrent_marking &&
+                      concurrent_marking_->Stop(
                           ConcurrentMarking::StopRequest::PREEMPT_TASKS)) {
   DCHECK_IMPLIES(resume_on_exit_, FLAG_concurrent_marking);
 }

src/heap/heap.cc

@@ -4310,7 +4310,7 @@ void Heap::SetUp() {
       new IncrementalMarking(this, mark_compact_collector_->marking_worklist(),
                              mark_compact_collector_->weak_objects());
 
-  if (FLAG_concurrent_marking) {
+  if (FLAG_concurrent_marking || FLAG_parallel_marking) {
     MarkCompactCollector::MarkingWorklist* marking_worklist =
         mark_compact_collector_->marking_worklist();
     concurrent_marking_ = new ConcurrentMarking(

src/heap/mark-compact-inl.h

@@ -331,7 +331,7 @@ int MarkingVisitor<fixed_array_mode, retaining_path_mode, MarkingState>::
       // Ensure that the object is either grey or black before pushing it
       // into marking worklist.
       marking_state()->WhiteToGrey(object);
-      if (FLAG_concurrent_marking) {
+      if (FLAG_concurrent_marking || FLAG_parallel_marking) {
         marking_worklist()->PushBailout(object);
       } else {
         marking_worklist()->Push(object);

src/heap/mark-compact.cc

@@ -780,7 +780,9 @@ void MarkCompactCollector::Prepare() {
 
 void MarkCompactCollector::FinishConcurrentMarking(
     ConcurrentMarking::StopRequest stop_request) {
-  if (FLAG_concurrent_marking) {
+  // FinishConcurrentMarking is called for both, concurrent and parallel,
+  // marking. It is safe to call this function when tasks are already finished.
+  if (FLAG_parallel_marking || FLAG_concurrent_marking) {
     heap()->concurrent_marking()->Stop(stop_request);
     heap()->concurrent_marking()->FlushLiveBytes(non_atomic_marking_state());
   }
@@ -1458,7 +1460,6 @@ void MarkCompactCollector::ProcessEphemeronsUntilFixpoint() {
                GCTracer::Scope::MC_MARK_WEAK_CLOSURE_EPHEMERON_MARKING);
 
       if (FLAG_parallel_marking) {
-        DCHECK(FLAG_concurrent_marking);
         heap_->concurrent_marking()->RescheduleTasksIfNeeded();
       }
 
@@ -1738,7 +1739,6 @@ void MarkCompactCollector::MarkLiveObjects() {
   {
     TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_MAIN);
     if (FLAG_parallel_marking) {
-      DCHECK(FLAG_concurrent_marking);
       heap_->concurrent_marking()->RescheduleTasksIfNeeded();
     }
     ProcessMarkingWorklist();