Remove sequential sweeping mode and perform lazy sweeping when no sweeper threads are active.

src/mark-compact.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/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/cpu-profiler.h"
@@ skipping 570 matching lines @@
     V8::GetCurrentPlatform()->CallOnBackgroundThread(
         new SweeperTask(heap(), heap()->old_data_space()),
         v8::Platform::kShortRunningTask);
     V8::GetCurrentPlatform()->CallOnBackgroundThread(
         new SweeperTask(heap(), heap()->old_pointer_space()),
         v8::Platform::kShortRunningTask);
   }
 }
 
 
 void MarkCompactCollector::WaitUntilSweepingCompleted() {

[Jarin, 2014/07/11 07:40:52]

Nit: WaitUntilSweepingCompleted -> EnsureSweepingCompleted?

[Hannes Payer (out of office), 2014/07/11 09:36:13]

Done.

   ASSERT(sweeping_pending_ == true);
+
+  // If sweeping is not completed, we try to complete it here. If we do not
+  // have sweeper threads we have to complete since we do not have a good
+  // indicator for a swept space in that case.
+  if (!AreSweeperThreadsActivated() || !IsSweepingCompleted()) {
+    SweepInParallel(heap()->paged_space(OLD_DATA_SPACE), 0);
+    SweepInParallel(heap()->paged_space(OLD_POINTER_SPACE), 0);
+  }
+
   for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
     isolate()->sweeper_threads()[i]->WaitForSweeperThread();
   }
   if (FLAG_job_based_sweeping) {
     // Wait twice for both jobs.
     pending_sweeper_jobs_semaphore_.Wait();
     pending_sweeper_jobs_semaphore_.Wait();
   }
   ParallelSweepSpacesComplete();
   sweeping_pending_ = false;
   RefillFreeList(heap()->paged_space(OLD_DATA_SPACE));
   RefillFreeList(heap()->paged_space(OLD_POINTER_SPACE));
   heap()->paged_space(OLD_DATA_SPACE)->ResetUnsweptFreeBytes();
   heap()->paged_space(OLD_POINTER_SPACE)->ResetUnsweptFreeBytes();
 }
 
 
 bool MarkCompactCollector::IsSweepingCompleted() {

[Jarin, 2014/07/11 07:40:52]

Nit: rename IsSweepingCompleted to IsConcurrentSweepingCompleted?

[Hannes Payer (out of office), 2014/07/11 09:36:13]

I left a comment for non-concurrent sweeping, instaed of renaming it since it is
also called in the non-concurrent case. WDYT?

   for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
     if (!isolate()->sweeper_threads()[i]->SweepingCompleted()) {
       return false;
     }
   }
+
   if (FLAG_job_based_sweeping) {
     if (!pending_sweeper_jobs_semaphore_.WaitFor(
             base::TimeDelta::FromSeconds(0))) {
       return false;
     }
     pending_sweeper_jobs_semaphore_.Signal();
   }
   return true;
 }
 
@@ skipping 15 matching lines @@
   space->AddToAccountingStats(freed_bytes);
   space->DecrementUnsweptFreeBytes(freed_bytes);
 }
 
 
 bool MarkCompactCollector::AreSweeperThreadsActivated() {
   return isolate()->sweeper_threads() != NULL || FLAG_job_based_sweeping;
 }
 
 
-bool MarkCompactCollector::IsConcurrentSweepingInProgress(PagedSpace* space) {
-  return (space == NULL || space->is_swept_concurrently()) &&
-      sweeping_pending_;
-}
-
-
 void Marking::TransferMark(Address old_start, Address new_start) {
   // This is only used when resizing an object.
   ASSERT(MemoryChunk::FromAddress(old_start) ==
          MemoryChunk::FromAddress(new_start));
 
   if (!heap_->incremental_marking()->IsMarking()) return;
 
   // If the mark doesn't move, we don't check the color of the object.
   // It doesn't matter whether the object is black, since it hasn't changed
   // size, so the adjustment to the live data count will be zero anyway.
@@ skipping 285 matching lines @@
   // variable.
   tracer_ = tracer;
 
 #ifdef DEBUG
   ASSERT(state_ == IDLE);
   state_ = PREPARE_GC;
 #endif
 
   ASSERT(!FLAG_never_compact || !FLAG_always_compact);
 
-  if (IsConcurrentSweepingInProgress()) {
+  if (sweeping_pending()) {
     // Instead of waiting we could also abort the sweeper threads here.
     WaitUntilSweepingCompleted();
   }
 
   // Clear marking bits if incremental marking is aborted.
   if (was_marked_incrementally_ && abort_incremental_marking_) {
     heap()->incremental_marking()->Abort();
     ClearMarkbits();
     AbortCompaction();
     was_marked_incrementally_ = false;
@@ skipping 3117 matching lines @@
       max_freed_overall = Max(max_freed, max_freed_overall);
     }
     if (p == space->end_of_unswept_pages()) break;
   }
   return max_freed_overall;
 }
 
 
 void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
   space->set_is_iterable(sweeper == PRECISE);
-  space->set_is_swept_concurrently(sweeper == CONCURRENT_CONSERVATIVE);
   space->ClearStats();
 
   // We defensively initialize end_of_unswept_pages_ here with the first page
   // of the pages list.
   space->set_end_of_unswept_pages(space->FirstPage());
 
   PageIterator it(space);
 
   int pages_swept = 0;
   bool unused_page_present = false;
@@ skipping 24 matching lines @@
         // Adjust unswept free bytes because releasing a page expects said
         // counter to be accurate for unswept pages.
         space->IncreaseUnsweptFreeBytes(p);
         space->ReleasePage(p);
         continue;
       }
       unused_page_present = true;
     }
 
     switch (sweeper) {
-      case CONSERVATIVE: {
-        if (FLAG_gc_verbose) {
-          PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
-                 reinterpret_cast<intptr_t>(p));
-        }
-        SweepConservatively<SWEEP_ON_MAIN_THREAD>(space, NULL, p);
-        pages_swept++;
-        break;
-      }
       case CONCURRENT_CONSERVATIVE:
       case PARALLEL_CONSERVATIVE: {
         if (!parallel_sweeping_active) {
           if (FLAG_gc_verbose) {
             PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
                    reinterpret_cast<intptr_t>(p));
           }
           SweepConservatively<SWEEP_ON_MAIN_THREAD>(space, NULL, p);
           pages_swept++;
           parallel_sweeping_active = true;
@@ skipping 41 matching lines @@
   // Give pages that are queued to be freed back to the OS.
   heap()->FreeQueuedChunks();
 }
 
 
 void MarkCompactCollector::SweepSpaces() {
   GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_SWEEP);
 #ifdef DEBUG
   state_ = SWEEP_SPACES;
 #endif
-  SweeperType how_to_sweep = CONSERVATIVE;
-  if (AreSweeperThreadsActivated()) {
-    if (FLAG_parallel_sweeping) how_to_sweep = PARALLEL_CONSERVATIVE;
-    if (FLAG_concurrent_sweeping) how_to_sweep = CONCURRENT_CONSERVATIVE;
-  }
+  SweeperType how_to_sweep = CONCURRENT_CONSERVATIVE;
+  if (FLAG_parallel_sweeping) how_to_sweep = PARALLEL_CONSERVATIVE;
+  if (FLAG_concurrent_sweeping) how_to_sweep = CONCURRENT_CONSERVATIVE;

[Jarin, 2014/07/11 07:40:52]

Is this is needed? CONCURRENT_CONSERVATIVE is the default anyway.

[Hannes Payer (out of office), 2014/07/11 09:36:13]

I think it is good to initialize it.

+
   if (sweep_precisely_) how_to_sweep = PRECISE;
 
   MoveEvacuationCandidatesToEndOfPagesList();
 
   // Noncompacting collections simply sweep the spaces to clear the mark
   // bits and free the nonlive blocks (for old and map spaces).  We sweep
   // the map space last because freeing non-live maps overwrites them and
   // the other spaces rely on possibly non-live maps to get the sizes for
   // non-live objects.
   { GCTracer::Scope sweep_scope(tracer_, GCTracer::Scope::MC_SWEEP_OLDSPACE);
@@ skipping 276 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal