Do not delay sweeping of pages that are completely free.

src/mark-compact.cc

 // Copyright 2011 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 3605 matching lines @@
     if (p->IsEvacuationCandidate()) {
       ASSERT(evacuation_candidates_.length() > 0);
       continue;
     }
 
     if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
       // Will be processed in EvacuateNewSpaceAndCandidates.
       continue;
     }
 
-    if (lazy_sweeping_active) {
-      if (FLAG_gc_verbose) {
-        PrintF("Sweeping 0x%" V8PRIxPTR " lazily postponed.\n",
-               reinterpret_cast<intptr_t>(p));
-      }
-      continue;
-    }
-
     // One unused page is kept, all further are released before sweeping them.
     if (p->LiveBytes() == 0) {
       if (unused_page_present) {
         if (FLAG_gc_verbose) {
           PrintF("Sweeping 0x%" V8PRIxPTR " released page.\n",
                  reinterpret_cast<intptr_t>(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));
+      }
+      continue;
+    }
+
     switch (sweeper) {
       case CONSERVATIVE: {
         if (FLAG_gc_verbose) {
           PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
                  reinterpret_cast<intptr_t>(p));
         }
         SweepConservatively(space, p);
         pages_swept++;
         break;
       }
@@ skipping 246 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal