Tweak compaction candidate selection to avoid keeping page with low occupancy around.

src/mksnapshot.cc

 // Copyright 2006-2008 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 294 matching lines @@
   Persistent<Context> context = v8::Context::New();
   ASSERT(!context.IsEmpty());
   // Make sure all builtin scripts are cached.
   { HandleScope scope;
     for (int i = 0; i < i::Natives::GetBuiltinsCount(); i++) {
       i::Isolate::Current()->bootstrapper()->NativesSourceLookup(i);
     }
   }
   // If we don't do this then we end up with a stray root pointing at the
   // context even after we have disposed of the context.
-  HEAP->CollectAllGarbage(i::Heap::kNoGCFlags);
+  HEAP->CollectAllGarbage(i::Heap::kNoGCFlags, "mksnapshot");
   i::Object* raw_context = *(v8::Utils::OpenHandle(*context));
   context.Dispose();
   CppByteSink sink(argv[1]);
   // This results in a somewhat smaller snapshot, probably because it gets rid
   // of some things that are cached between garbage collections.
   i::StartupSerializer ser(&sink);
   ser.SerializeStrongReferences();
 
   i::PartialSerializer partial_ser(&ser, sink.partial_sink());
   partial_ser.Serialize(&raw_context);
@@ skipping 13 matching lines @@
   sink.WriteSpaceUsed(
       partial_ser.CurrentAllocationAddress(i::NEW_SPACE),
       partial_ser.CurrentAllocationAddress(i::OLD_POINTER_SPACE),
       partial_ser.CurrentAllocationAddress(i::OLD_DATA_SPACE),
       partial_ser.CurrentAllocationAddress(i::CODE_SPACE),
       partial_ser.CurrentAllocationAddress(i::MAP_SPACE),
       partial_ser.CurrentAllocationAddress(i::CELL_SPACE),
       partial_ser.CurrentAllocationAddress(i::LO_SPACE));
   return 0;
 }