Precisely sweep scan on scavenge pages and use heap iterator to iterate over them.

src/store-buffer.cc

 // Copyright 2011 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/store-buffer.h"
 
 #include <algorithm>
 
 #include "src/v8.h"
 
@@ skipping 534 matching lines @@
           FindPointersToNewSpaceInRegion(start, end, slot_callback, clear_maps);
         } else {
           Page* page = reinterpret_cast<Page*>(chunk);
           PagedSpace* owner = reinterpret_cast<PagedSpace*>(page->owner());
           Address start = page->area_start();
           Address end = page->area_end();
           if (owner == heap_->map_space()) {
             FindPointersToNewSpaceInMapsRegion(
                 start, end, slot_callback, clear_maps);
           } else {
-            FindPointersToNewSpaceInRegion(
-                start, end, slot_callback, clear_maps);
+            ASSERT(page->WasSweptPrecisely());
+            HeapObjectIterator iterator(page, NULL);
+            for (HeapObject* heap_object = iterator.Next();
+                 heap_object != NULL;
+                 heap_object = iterator.Next()) {
+              // We skip filler, free space, and constant pool objects.

[rmcilroy, 2014/07/02 12:39:07]

Could you add back the old comment here please:

// Skip fillers, free space, and constant pool arrays (which never 
// contain new-space pointers but can contain pointers which can 
// be confused for fillers).

+              if (!heap_object->IsFiller() &&
+                  !heap_object->IsConstantPoolArray()) {
+                FindPointersToNewSpaceInRegion(
+                    heap_object->address() + HeapObject::kHeaderSize,
+                    heap_object->address() + heap_object->Size(),
+                    slot_callback,
+                    clear_maps);
+              }
+            }
           }
         }
       }
     }
     if (callback_ != NULL) {
       (*callback_)(heap_, NULL, kStoreBufferScanningPageEvent);
     }
   }
 }
 
@@ skipping 45 matching lines @@
     }
     old_buffer_is_sorted_ = false;
     old_buffer_is_filtered_ = false;
     *old_top_++ = reinterpret_cast<Address>(int_addr << kPointerSizeLog2);
     ASSERT(old_top_ <= old_limit_);
   }
   heap_->isolate()->counters()->store_buffer_compactions()->Increment();
 }
 
 } }  // namespace v8::internal