An object should only be promoted to the old generation if it survived a scavenge operation.

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 1957 matching lines @@
       if (marking_deque->IsFull()) return;
       offset += 2;
       grey_objects >>= 2;
     }
 
     grey_objects >>= (Bitmap::kBitsPerCell - 1);
   }
 }
 
 
 int MarkCompactCollector::DiscoverAndPromoteBlackObjectsOnPage(

[Michael Starzinger, 2014/06/18 10:46:39]

nit: IMHO the name of this function no longer applies, should be maybe rename it
to "DiscoverAndMigrateBlackObjectsOnPage"?

[Hannes Payer (out of office), 2014/06/18 11:40:29]

I renamed it to DiscoverAndEvacuateBlackObjectsOnPage.

     NewSpace* new_space,
     NewSpacePage* p) {
   ASSERT(strcmp(Marking::kWhiteBitPattern, "00") == 0);
   ASSERT(strcmp(Marking::kBlackBitPattern, "10") == 0);
   ASSERT(strcmp(Marking::kGreyBitPattern, "11") == 0);
   ASSERT(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
 
   MarkBit::CellType* cells = p->markbits()->cells();
   int survivors_size = 0;
 
@@ skipping 12 matching lines @@
       Address address = cell_base + offset * kPointerSize;
       HeapObject* object = HeapObject::FromAddress(address);
 
       int size = object->Size();
       survivors_size += size;
 
       Heap::UpdateAllocationSiteFeedback(object, Heap::RECORD_SCRATCHPAD_SLOT);
 
       offset++;
       current_cell >>= 1;
-      // Aggressively promote young survivors to the old space.
-      if (TryPromoteObject(object, size)) {
+
+      // TODO(hpayer): Refactor EvacuateObject and call this function instead.
+      if (heap_->ShouldBePromoted(object->address(), size) &&

[Michael Starzinger, 2014/06/18 10:46:39]

nit: s/heap_/heap()/

[Hannes Payer (out of office), 2014/06/18 11:40:29]

Done.

+          TryPromoteObject(object, size)) {
         continue;
       }
 
       // Promotion failed. Just migrate object to another semispace.
       AllocationResult allocation = new_space->AllocateRaw(size);
       if (allocation.IsRetry()) {
         if (!new_space->AddFreshPage()) {
           // Shouldn't happen. We are sweeping linearly, and to-space
           // has the same number of pages as from-space, so there is
           // always room.
@@ skipping 2442 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal