Revert of [heap] Start sweeper tasks after evacuation.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 5be69a10d1fcddc6cfba672954111ef8d672784c..ee04ee846d68b76a35c8b7cae2bcb790ad0252eb 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -321,7 +321,7 @@
   }
 #endif
 
-  StartSweepSpaces();
+  SweepSpaces();
 
   EvacuateNewSpaceAndCandidates();
 
@@ -451,18 +451,20 @@
     std::sort(sweeping_list_[space].begin(), sweeping_list_[space].end(),
               [](Page* a, Page* b) { return a->LiveBytes() < b->LiveBytes(); });
   });
-}
-
-void MarkCompactCollector::Sweeper::StartSweeperTasks() {
-  if (FLAG_concurrent_sweeping && sweeping_in_progress_) {
+  if (FLAG_concurrent_sweeping) {
     ForAllSweepingSpaces([this](AllocationSpace space) {
       if (space == NEW_SPACE) return;
-      num_sweeping_tasks_.Increment(1);
-      V8::GetCurrentPlatform()->CallOnBackgroundThread(
-          new SweeperTask(this, &pending_sweeper_tasks_semaphore_, space),
-          v8::Platform::kShortRunningTask);
+      StartSweepingHelper(space);
     });
   }
+}
+
+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(
@@ -479,8 +481,7 @@
 }
 
 void MarkCompactCollector::SweepAndRefill(CompactionSpace* space) {
-  if (FLAG_concurrent_sweeping &&
-      !sweeper().IsSweepingCompleted(space->identity())) {
+  if (FLAG_concurrent_sweeping && !sweeper().IsSweepingCompleted()) {
     sweeper().ParallelSweepSpace(space->identity(), 0);
     space->RefillFreeList();
   }
@@ -500,11 +501,10 @@
 
   // If sweeping is not completed or not running at all, we try to complete it
   // here.
-  ForAllSweepingSpaces([this](AllocationSpace space) {
-    if (!FLAG_concurrent_sweeping || !this->IsSweepingCompleted(space)) {
-      ParallelSweepSpace(space, 0);
-    }
-  });
+  if (!FLAG_concurrent_sweeping || !IsSweepingCompleted()) {
+    ForAllSweepingSpaces(
+        [this](AllocationSpace space) { ParallelSweepSpace(space, 0); });
+  }
 
   if (FLAG_concurrent_sweeping) {
     while (num_sweeping_tasks_.Value() > 0) {
@@ -519,12 +519,13 @@
     }
     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(NEW_SPACE)) {
+  if (!FLAG_concurrent_sweeping || !IsSweepingCompleted()) {
     for (Page* p : *heap_->new_space()) {
       SweepOrWaitUntilSweepingCompleted(p);
     }
@@ -546,20 +547,13 @@
 #endif
 }
 
-bool MarkCompactCollector::Sweeper::AreSweeperTasksRunning() {
+bool MarkCompactCollector::Sweeper::IsSweepingCompleted() {
   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;
-}
-
-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();
+  return num_sweeping_tasks_.Value() == 0;
 }
 
 const char* AllocationSpaceName(AllocationSpace space) {
@@ -838,7 +832,11 @@
 void MarkCompactCollector::Finish() {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_FINISH);
 
-  sweeper().StartSweeperTasks();
+  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);
+  }
 
   // The hashing of weak_object_to_code_table is no longer valid.
   heap()->weak_object_to_code_table()->Rehash(
@@ -3175,15 +3173,17 @@
   //
   // The number of parallel compaction tasks is limited by:
   // - #evacuation pages
-  // - #cores
+  // - (#cores - 1)
   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()));
+             V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads()) -
+             kNumSweepingTasks - 1);
   int tasks;
   if (compaction_speed > 0) {
     tasks = 1 + static_cast<int>(live_bytes / compaction_speed /
@@ -3543,12 +3543,12 @@
     for (Page* p : newspace_evacuation_candidates_) {
       if (p->IsFlagSet(Page::PAGE_NEW_NEW_PROMOTION)) {
         p->ClearFlag(Page::PAGE_NEW_NEW_PROMOTION);
-        sweeper().AddPage(p->owner()->identity(), p);
+        sweeper().AddLatePage(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().AddPage(p->owner()->identity(), p);
+        sweeper().AddLatePage(p->owner()->identity(), p);
       }
     }
     newspace_evacuation_candidates_.Rewind(0);
@@ -3560,7 +3560,7 @@
       SkipList* list = p->skip_list();
       if (list != NULL) list->Clear();
       if (p->IsFlagSet(Page::COMPACTION_WAS_ABORTED)) {
-        sweeper().AddPage(p->owner()->identity(), p);
+        sweeper().AddLatePage(p->owner()->identity(), p);
         p->ClearFlag(Page::COMPACTION_WAS_ABORTED);
       }
     }
@@ -3862,9 +3862,17 @@
 }
 
 void MarkCompactCollector::Sweeper::AddPage(AllocationSpace space, Page* page) {
-  DCHECK(!FLAG_concurrent_sweeping || !AreSweeperTasksRunning());
+  DCHECK(!sweeping_in_progress_);
   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,
@@ -3947,7 +3955,8 @@
   }
 }
 
-void MarkCompactCollector::StartSweepSpaces() {
+
+void MarkCompactCollector::SweepSpaces() {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_SWEEP);
 #ifdef DEBUG
   state_ = SWEEP_SPACES;