[heap] Start sweeper tasks after evacuation.

This allows us to use more tasks for parallel evacuation.

BUG=

Review-Url: https://chromiumcodereview.appspot.com/2428043002
Cr-Commit-Position: refs/heads/master@{#40444}

src/heap/incremental-marking.cc

@@ -1053,7 +1053,7 @@ void IncrementalMarking::FinalizeSweeping() {
   DCHECK(state_ == SWEEPING);
   if (heap_->mark_compact_collector()->sweeping_in_progress() &&
       (!FLAG_concurrent_sweeping ||
-       heap_->mark_compact_collector()->sweeper().IsSweepingCompleted())) {
+       !heap_->mark_compact_collector()->sweeper().AreSweeperTasksRunning())) {
     heap_->mark_compact_collector()->EnsureSweepingCompleted();
   }
   if (!heap_->mark_compact_collector()->sweeping_in_progress()) {

src/heap/mark-compact.cc

@@ -321,7 +321,7 @@ void MarkCompactCollector::CollectGarbage() {
   }
 #endif
 
-  SweepSpaces();
+  StartSweepSpaces();
 
   EvacuateNewSpaceAndCandidates();
 
@@ -451,22 +451,20 @@ void MarkCompactCollector::Sweeper::StartSweeping() {
     std::sort(sweeping_list_[space].begin(), sweeping_list_[space].end(),
               [](Page* a, Page* b) { return a->LiveBytes() < b->LiveBytes(); });
   });
-  if (FLAG_concurrent_sweeping) {
+}
+
+void MarkCompactCollector::Sweeper::StartSweeperTasks() {
+  if (FLAG_concurrent_sweeping && sweeping_in_progress_) {
     ForAllSweepingSpaces([this](AllocationSpace space) {
       if (space == NEW_SPACE) return;
-      StartSweepingHelper(space);
+      num_sweeping_tasks_.Increment(1);
+      V8::GetCurrentPlatform()->CallOnBackgroundThread(
+          new SweeperTask(this, &pending_sweeper_tasks_semaphore_, space),
+          v8::Platform::kShortRunningTask);
     });
   }
 }
 
-void MarkCompactCollector::Sweeper::StartSweepingHelper(
-    AllocationSpace space_to_start) {
-  num_sweeping_tasks_.Increment(1);
-  V8::GetCurrentPlatform()->CallOnBackgroundThread(
-      new SweeperTask(this, &pending_sweeper_tasks_semaphore_, space_to_start),
-      v8::Platform::kShortRunningTask);
-}
-
 void MarkCompactCollector::Sweeper::SweepOrWaitUntilSweepingCompleted(
     Page* page) {
   if (!page->SweepingDone()) {
@@ -481,7 +479,8 @@ void MarkCompactCollector::Sweeper::SweepOrWaitUntilSweepingCompleted(
 }
 
 void MarkCompactCollector::SweepAndRefill(CompactionSpace* space) {
-  if (FLAG_concurrent_sweeping && !sweeper().IsSweepingCompleted()) {
+  if (FLAG_concurrent_sweeping &&
+      !sweeper().IsSweepingCompleted(space->identity())) {
     sweeper().ParallelSweepSpace(space->identity(), 0);
     space->RefillFreeList();
   }
@@ -501,10 +500,11 @@ void MarkCompactCollector::Sweeper::EnsureCompleted() {
 
   // If sweeping is not completed or not running at all, we try to complete it
   // here.
-  if (!FLAG_concurrent_sweeping || !IsSweepingCompleted()) {
-    ForAllSweepingSpaces(
-        [this](AllocationSpace space) { ParallelSweepSpace(space, 0); });
-  }
+  ForAllSweepingSpaces([this](AllocationSpace space) {
+    if (!FLAG_concurrent_sweeping || !this->IsSweepingCompleted(space)) {
+      ParallelSweepSpace(space, 0);
+    }
+  });
 
   if (FLAG_concurrent_sweeping) {
     while (num_sweeping_tasks_.Value() > 0) {
@@ -519,13 +519,12 @@ void MarkCompactCollector::Sweeper::EnsureCompleted() {
     }
     DCHECK(sweeping_list_[space].empty());
   });
-  late_pages_ = false;
   sweeping_in_progress_ = false;
 }
 
 void MarkCompactCollector::Sweeper::EnsureNewSpaceCompleted() {
   if (!sweeping_in_progress_) return;
-  if (!FLAG_concurrent_sweeping || !IsSweepingCompleted()) {
+  if (!FLAG_concurrent_sweeping || !IsSweepingCompleted(NEW_SPACE)) {
     for (Page* p : *heap_->new_space()) {
       SweepOrWaitUntilSweepingCompleted(p);
     }
@@ -547,13 +546,20 @@ void MarkCompactCollector::EnsureSweepingCompleted() {
 #endif
 }
 
-bool MarkCompactCollector::Sweeper::IsSweepingCompleted() {
+bool MarkCompactCollector::Sweeper::AreSweeperTasksRunning() {
   DCHECK(FLAG_concurrent_sweeping);
   while (pending_sweeper_tasks_semaphore_.WaitFor(
       base::TimeDelta::FromSeconds(0))) {
     num_sweeping_tasks_.Increment(-1);
   }
-  return num_sweeping_tasks_.Value() == 0;
+  return num_sweeping_tasks_.Value() != 0;
+}
+
+bool MarkCompactCollector::Sweeper::IsSweepingCompleted(AllocationSpace space) {
+  DCHECK(FLAG_concurrent_sweeping);
+  if (AreSweeperTasksRunning()) return false;
+  base::LockGuard<base::Mutex> guard(&mutex_);
+  return sweeping_list_[space].empty();
 }
 
 const char* AllocationSpaceName(AllocationSpace space) {
@@ -832,11 +838,7 @@ void MarkCompactCollector::Prepare() {
 void MarkCompactCollector::Finish() {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_FINISH);
 
-  if (sweeper().contains_late_pages() && FLAG_concurrent_sweeping) {
-    // If we added some more pages during MC, we need to start at least one
-    // more task as all other tasks might already be finished.
-    sweeper().StartSweepingHelper(OLD_SPACE);
-  }
+  sweeper().StartSweeperTasks();
 
   // The hashing of weak_object_to_code_table is no longer valid.
   heap()->weak_object_to_code_table()->Rehash(
@@ -3173,17 +3175,15 @@ int MarkCompactCollector::NumberOfParallelCompactionTasks(int pages,
   //
   // The number of parallel compaction tasks is limited by:
   // - #evacuation pages
-  // - (#cores - 1)
+  // - #cores
   const double kTargetCompactionTimeInMs = .5;
-  const int kNumSweepingTasks = 3;
 
   double compaction_speed =
       heap()->tracer()->CompactionSpeedInBytesPerMillisecond();
 
   const int available_cores = Max(
       1, static_cast<int>(
-             V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads()) -
-             kNumSweepingTasks - 1);
+             V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads()));
   int tasks;
   if (compaction_speed > 0) {
     tasks = 1 + static_cast<int>(live_bytes / compaction_speed /
@@ -3543,12 +3543,12 @@ void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
     for (Page* p : newspace_evacuation_candidates_) {
       if (p->IsFlagSet(Page::PAGE_NEW_NEW_PROMOTION)) {
         p->ClearFlag(Page::PAGE_NEW_NEW_PROMOTION);
-        sweeper().AddLatePage(p->owner()->identity(), p);
+        sweeper().AddPage(p->owner()->identity(), p);
       } else if (p->IsFlagSet(Page::PAGE_NEW_OLD_PROMOTION)) {
         p->ClearFlag(Page::PAGE_NEW_OLD_PROMOTION);
         p->ForAllFreeListCategories(
             [](FreeListCategory* category) { DCHECK(!category->is_linked()); });
-        sweeper().AddLatePage(p->owner()->identity(), p);
+        sweeper().AddPage(p->owner()->identity(), p);
       }
     }
     newspace_evacuation_candidates_.Rewind(0);
@@ -3560,7 +3560,7 @@ void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
       SkipList* list = p->skip_list();
       if (list != NULL) list->Clear();
       if (p->IsFlagSet(Page::COMPACTION_WAS_ABORTED)) {
-        sweeper().AddLatePage(p->owner()->identity(), p);
+        sweeper().AddPage(p->owner()->identity(), p);
         p->ClearFlag(Page::COMPACTION_WAS_ABORTED);
       }
     }
@@ -3862,19 +3862,11 @@ int MarkCompactCollector::Sweeper::ParallelSweepPage(Page* page,
 }
 
 void MarkCompactCollector::Sweeper::AddPage(AllocationSpace space, Page* page) {
-  DCHECK(!sweeping_in_progress_);
+  DCHECK(!FLAG_concurrent_sweeping || !AreSweeperTasksRunning());
   PrepareToBeSweptPage(space, page);
   sweeping_list_[space].push_back(page);
 }
 
-void MarkCompactCollector::Sweeper::AddLatePage(AllocationSpace space,
-                                                Page* page) {
-  DCHECK(sweeping_in_progress_);
-  PrepareToBeSweptPage(space, page);
-  late_pages_ = true;
-  AddSweepingPageSafe(space, page);
-}
-
 void MarkCompactCollector::Sweeper::PrepareToBeSweptPage(AllocationSpace space,
                                                          Page* page) {
   page->concurrent_sweeping_state().SetValue(Page::kSweepingPending);
@@ -3955,8 +3947,7 @@ void MarkCompactCollector::StartSweepSpace(PagedSpace* space) {
   }
 }
 
-
-void MarkCompactCollector::SweepSpaces() {
+void MarkCompactCollector::StartSweepSpaces() {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_SWEEP);
 #ifdef DEBUG
   state_ = SWEEP_SPACES;

src/heap/mark-compact.h

@@ -299,24 +299,25 @@ class MarkCompactCollector {
         : heap_(heap),
           pending_sweeper_tasks_semaphore_(0),
           sweeping_in_progress_(false),
-          late_pages_(false),
           num_sweeping_tasks_(0) {}
 
     bool sweeping_in_progress() { return sweeping_in_progress_; }
-    bool contains_late_pages() { return late_pages_; }
 
     void AddPage(AllocationSpace space, Page* page);
-    void AddLatePage(AllocationSpace space, Page* page);
 
     int ParallelSweepSpace(AllocationSpace identity, int required_freed_bytes,
                            int max_pages = 0);
     int ParallelSweepPage(Page* page, AllocationSpace identity);
 
+    // After calling this function sweeping is considered to be in progress
+    // and the main thread can sweep lazily, but the background sweeper tasks
+    // are not running yet.
     void StartSweeping();
-    void StartSweepingHelper(AllocationSpace space_to_start);
+    void StartSweeperTasks();
     void EnsureCompleted();
     void EnsureNewSpaceCompleted();
-    bool IsSweepingCompleted();
+    bool AreSweeperTasksRunning();
+    bool IsSweepingCompleted(AllocationSpace space);
     void SweepOrWaitUntilSweepingCompleted(Page* page);
 
     void AddSweptPageSafe(PagedSpace* space, Page* page);
@@ -343,7 +344,6 @@ class MarkCompactCollector {
     SweptList swept_list_[kAllocationSpaces];
     SweepingList sweeping_list_[kAllocationSpaces];
     bool sweeping_in_progress_;
-    bool late_pages_;
     base::AtomicNumber<intptr_t> num_sweeping_tasks_;
   };
 
@@ -643,21 +643,10 @@ class MarkCompactCollector {
 
   void AbortTransitionArrays();
 
-  // -----------------------------------------------------------------------
-  // Phase 2: Sweeping to clear mark bits and free non-live objects for
-  // a non-compacting collection.
-  //
-  //  Before: Live objects are marked and non-live objects are unmarked.
-  //
-  //   After: Live objects are unmarked, non-live regions have been added to
-  //          their space's free list. Active eden semispace is compacted by
-  //          evacuation.
-  //
-
-  // If we are not compacting the heap, we simply sweep the spaces except
-  // for the large object space, clearing mark bits and adding unmarked
-  // regions to each space's free list.
-  void SweepSpaces();
+  // Starts sweeping of spaces by contributing on the main thread and setting
+  // up other pages for sweeping. Does not start sweeper tasks.
+  void StartSweepSpaces();
+  void StartSweepSpace(PagedSpace* space);
 
   void EvacuateNewSpacePrologue();
 
@@ -680,9 +669,6 @@ class MarkCompactCollector {
 
   void ReleaseEvacuationCandidates();
 
-  // Starts sweeping of a space by contributing on the main thread and setting
-  // up other pages for sweeping.
-  void StartSweepSpace(PagedSpace* space);
 
 #ifdef DEBUG
   friend class MarkObjectVisitor;

src/heap/spaces.cc

@@ -394,12 +394,14 @@ void MemoryAllocator::Unmapper::ReconsiderDelayedChunks() {
 }
 
 bool MemoryAllocator::CanFreeMemoryChunk(MemoryChunk* chunk) {
-  MarkCompactCollector* mc = isolate_->heap()->mark_compact_collector();
   // We cannot free memory chunks in new space while the sweeper is running
   // since a sweeper thread might be stuck right before trying to lock the
   // corresponding page.
-  return !chunk->InNewSpace() || (mc == nullptr) || !FLAG_concurrent_sweeping ||
-         mc->sweeper().IsSweepingCompleted();
+
+  // Chunks in old generation are unmapped if they are empty.
+  DCHECK(chunk->InNewSpace() || chunk->SweepingDone());
+  return !chunk->InNewSpace() || !FLAG_concurrent_sweeping ||
+         chunk->SweepingDone();
 }
 
 bool MemoryAllocator::CommitMemory(Address base, size_t size,

src/heap/spaces.h

@@ -413,6 +413,10 @@ class MemoryChunk {
     return concurrent_sweeping_;
   }
 
+  bool SweepingDone() {
+    return concurrent_sweeping_state().Value() == kSweepingDone;
+  }
+
   // Manage live byte count, i.e., count of bytes in black objects.
   inline void ResetLiveBytes();
   inline void IncrementLiveBytes(int by);
@@ -767,10 +771,6 @@ class Page : public MemoryChunk {
     DCHECK(SweepingDone());
   }
 
-  bool SweepingDone() {
-    return concurrent_sweeping_state().Value() == kSweepingDone;
-  }
-
   void ResetFreeListStatistics();
 
   size_t AvailableInFreeList();