[PATCH] memory page_alloc zonelist caching reorder structure

Rearrange the struct members in the 'struct zonelist_cache' structure, so
as to put the readonly (once initialized) z_to_n[] array first, where it
will come right after the zones[] array in struct zonelist.

This pretty much eliminates the chance that the two frequently written
elements of 'struct zonelist_cache', the fullzones bitmap and last_full_zap
times, will end up on the same cache line as the performance sensitive,
frequently read, never (after init) written zones[] array.

Keeping frequently written data off frequently read cache lines is good for
performance.

Thanks to Rohit Seth for the suggestion.

Signed-off-by: Paul Jackson <pj@sgi.com>
Cc: Rohit Seth <rohitseth@google.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 09bf9d8..da6002d 100644 (file)
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -352,8 +352,8 @@ struct zone {
 
 
 struct zonelist_cache {
-       DECLARE_BITMAP(fullzones, MAX_ZONES_PER_ZONELIST);      /* zone full? */
        unsigned short z_to_n[MAX_ZONES_PER_ZONELIST];          /* zone->nid */
+       DECLARE_BITMAP(fullzones, MAX_ZONES_PER_ZONELIST);      /* zone full? */
        unsigned long last_full_zap;            /* when last zap'd (jiffies) */
 };
 #else