diff -r bbfc65d05588 Objects/obmalloc.c
--- a/Objects/obmalloc.c	Thu Apr 07 10:48:29 2011 -0400
+++ b/Objects/obmalloc.c	Mon Apr 25 15:10:43 2011 +0200
@@ -75,7 +75,8 @@
  * Allocation strategy abstract:
  *
  * For small requests, the allocator sub-allocates <Big> blocks of memory.
- * Requests greater than 256 bytes are routed to the system's allocator.
+ * Requests greater than SMALL_REQUEST_THRESHOLD bytes are routed to the
+ * system's allocator.
  *
  * Small requests are grouped in size classes spaced 8 bytes apart, due
  * to the required valid alignment of the returned address. Requests of
@@ -107,10 +108,11 @@
  *       57-64                   64                       7
  *       65-72                   72                       8
  *        ...                   ...                     ...
- *      241-248                 248                      30
- *      249-256                 256                      31
+ *      497-504                 504                      62
+ *      505-512                 512                      63
  *
- *      0, 257 and up: routed to the underlying allocator.
+ *      0, SMALL_REQUEST_THRESHOLD + 1 and up: routed to the underlying
+ *      allocator.
  */
 
 /*==========================================================================*/
@@ -139,14 +141,17 @@
  * small enough in order to use preallocated memory pools. You can tune
  * this value according to your application behaviour and memory needs.
  *
+ * Note: a size threshold of 512 guarantees that newly created dictionaries
+ * will be allocated from preallocated memory pools on 64-bit.
+ *
  * The following invariants must hold:
- *      1) ALIGNMENT <= SMALL_REQUEST_THRESHOLD <= 256
+ *      1) ALIGNMENT <= SMALL_REQUEST_THRESHOLD <= 512
  *      2) SMALL_REQUEST_THRESHOLD is evenly divisible by ALIGNMENT
  *
  * Although not required, for better performance and space efficiency,
  * it is recommended that SMALL_REQUEST_THRESHOLD is set to a power of 2.
  */
-#define SMALL_REQUEST_THRESHOLD 256
+#define SMALL_REQUEST_THRESHOLD 512
 #define NB_SMALL_SIZE_CLASSES   (SMALL_REQUEST_THRESHOLD / ALIGNMENT)
 
 /*
@@ -440,6 +445,9 @@
     , PT(48), PT(49), PT(50), PT(51), PT(52), PT(53), PT(54), PT(55)
 #if NB_SMALL_SIZE_CLASSES > 56
     , PT(56), PT(57), PT(58), PT(59), PT(60), PT(61), PT(62), PT(63)
+#if NB_SMALL_SIZE_CLASSES > 64
+#error "NB_SMALL_SIZE_CLASSES should be less than 64"
+#endif /* NB_SMALL_SIZE_CLASSES > 64 */
 #endif /* NB_SMALL_SIZE_CLASSES > 56 */
 #endif /* NB_SMALL_SIZE_CLASSES > 48 */
 #endif /* NB_SMALL_SIZE_CLASSES > 40 */