Only use FreeSpace objects in the free list.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 332d1ed92c42f4e3f75f759cc9d2d7ce7f76ecd4..d13e210fe29bf317792b36a2a05706ac75ba38b6 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -4448,8 +4448,10 @@ class ByteArray: public FixedArrayBase {
 };
 
 
-// FreeSpace represents fixed sized areas of the heap that are not currently in
-// use.  Used by the heap and GC.
+// FreeSpace are free blocks in the heap.  They look like heap objects

[Hannes Payer (out of office), 2015/01/27 08:05:49]

... are fixed size memory blocks...

[Yang, 2015/01/27 08:49:49]

Done.

+// (are heap object tagged and have a map) so that the heap remains iterable.
+// They have a size and a next pointer.  The next pointer is the raw address
+// of the next FreeSpace object (or NULL) in the free list.

[Hannes Payer (out of office), 2015/01/27 08:05:49]

Used by the heap and GC.

[Yang, 2015/01/27 08:49:49]

Done.

 class FreeSpace: public HeapObject {
  public:
   // [size]: size of the free space including the header.
@@ -4461,7 +4463,12 @@ class FreeSpace: public HeapObject {
 
   inline int Size() { return size(); }
 
-  DECLARE_CAST(FreeSpace)
+  // Accessors for the next field.
+  inline FreeSpace* next();
+  inline FreeSpace** next_address();
+  inline void set_next(FreeSpace* next);
+
+  inline static FreeSpace* cast(HeapObject* obj);
 
   // Dispatched behavior.
   DECLARE_PRINTER(FreeSpace)
@@ -4470,9 +4477,7 @@ class FreeSpace: public HeapObject {
   // Layout description.
   // Size is smi tagged when it is stored.
   static const int kSizeOffset = HeapObject::kHeaderSize;
-  static const int kHeaderSize = kSizeOffset + kPointerSize;
-
-  static const int kAlignedSize = OBJECT_POINTER_ALIGN(kHeaderSize);
+  static const int kNextOffset = POINTER_SIZE_ALIGN(kSizeOffset + kPointerSize);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(FreeSpace);