Never use the freelists when always compacting.

src/spaces.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 1314 matching lines @@
 
 int OldSpaceFreeList::Free(Address start, int size_in_bytes) {
 #ifdef DEBUG
   for (int i = 0; i < size_in_bytes; i += kPointerSize) {
     Memory::Address_at(start + i) = kZapValue;
   }
 #endif
   FreeListNode* node = FreeListNode::FromAddress(start);
   node->set_size(size_in_bytes);
 
+  // We don't use the freelists in compacting mode.  This makes it more like a
+  // GC that only has mark-sweep-compact and doesn't have a mark-sweep
+  // collector.
+  if (FLAG_always_compact) {
+    return size_in_bytes;
+  }
+
   // Early return to drop too-small blocks on the floor (one or two word
   // blocks cannot hold a map pointer, a size field, and a pointer to the
   // next block in the free list).
   if (size_in_bytes < kMinBlockSize) {
     return size_in_bytes;
   }
 
   // Insert other blocks at the head of an exact free list.
   int index = size_in_bytes >> kPointerSizeLog2;
   node->set_next(free_[index].head_node_);
@@ skipping 1273 matching lines @@
                      reinterpret_cast<Object**>(object->address()
                                                 + Page::kObjectAreaSize),
                      allocation_top);
       PrintF("\n");
     }
   }
 }
 #endif  // DEBUG
 
 } }  // namespace v8::internal