Presweep one page before parallel/concurrent sweeping.

src/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3752 matching lines @@
 
 void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
   space->set_was_swept_conservatively(sweeper == CONSERVATIVE ||
                                       sweeper == LAZY_CONSERVATIVE ||
                                       sweeper == PARALLEL_CONSERVATIVE ||
                                       sweeper == CONCURRENT_CONSERVATIVE);
   space->ClearStats();
 
   PageIterator it(space);
 
-  intptr_t freed_bytes = 0;
   int pages_swept = 0;
   bool lazy_sweeping_active = false;
   bool unused_page_present = false;
+  bool parallel_sweeping_active = false;
 
   while (it.has_next()) {
     Page* p = it.next();
 
     ASSERT(p->parallel_sweeping() == 0);
     // Clear sweeping flags indicating that marking bits are still intact.
     p->ClearSweptPrecisely();
     p->ClearSweptConservatively();
 
     if (p->IsEvacuationCandidate()) {
@@ skipping 15 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;
     }
 
-    if (lazy_sweeping_active) {
-      if (FLAG_gc_verbose) {
-        PrintF("Sweeping 0x%" V8PRIxPTR " lazily postponed.\n",
-               reinterpret_cast<intptr_t>(p));
-      }
-      space->IncreaseUnsweptFreeBytes(p);
-      continue;
-    }
-
     switch (sweeper) {
       case CONSERVATIVE: {
         if (FLAG_gc_verbose) {
           PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
                  reinterpret_cast<intptr_t>(p));
         }
         SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
         pages_swept++;
         break;
       }
       case LAZY_CONSERVATIVE: {
-        if (FLAG_gc_verbose) {
-          PrintF("Sweeping 0x%" V8PRIxPTR " conservatively as needed.\n",
-                 reinterpret_cast<intptr_t>(p));
+        if (lazy_sweeping_active) {
+          if (FLAG_gc_verbose) {
+            PrintF("Sweeping 0x%" V8PRIxPTR " lazily postponed.\n",
+                   reinterpret_cast<intptr_t>(p));
+          }
+          space->IncreaseUnsweptFreeBytes(p);
+        } else {
+          if (FLAG_gc_verbose) {
+            PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
+                   reinterpret_cast<intptr_t>(p));
+          }
+          SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
+          pages_swept++;
+          space->SetPagesToSweep(p->next_page());
+          lazy_sweeping_active = true;
         }
-        freed_bytes += SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
-        pages_swept++;
-        space->SetPagesToSweep(p->next_page());
-        lazy_sweeping_active = true;
         break;
       }
       case CONCURRENT_CONSERVATIVE:
       case PARALLEL_CONSERVATIVE: {
-        if (FLAG_gc_verbose) {
-          PrintF("Sweeping 0x%" V8PRIxPTR " conservatively in parallel.\n",
-                 reinterpret_cast<intptr_t>(p));
+        if (!parallel_sweeping_active) {
+          if (FLAG_gc_verbose) {
+            PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
+                   reinterpret_cast<intptr_t>(p));
+          }
+          SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
+          pages_swept++;
+          parallel_sweeping_active = true;
+        } else {
+          if (FLAG_gc_verbose) {
+            PrintF("Sweeping 0x%" V8PRIxPTR " conservatively in parallel.\n",
+                   reinterpret_cast<intptr_t>(p));
+          }
+          p->set_parallel_sweeping(1);
+          space->IncreaseUnsweptFreeBytes(p);
         }
-        p->set_parallel_sweeping(1);
-        space->IncreaseUnsweptFreeBytes(p);
         break;
       }
       case PRECISE: {
         if (FLAG_gc_verbose) {
           PrintF("Sweeping 0x%" V8PRIxPTR " precisely.\n",
                  reinterpret_cast<intptr_t>(p));
         }
         if (space->identity() == CODE_SPACE) {
           SweepPrecisely<SWEEP_ONLY, REBUILD_SKIP_LIST>(space, p, NULL);
         } else {
@@ skipping 260 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal