[rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment

Nick Piggin
2008-03-03T09:35:06Z

SLUB should pack even small objects nicely into cachelines if that is what
has been asked for. Use the same algorithm as SLAB for this.

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c
+++ linux-2.6/mm/slub.c
@@ -1896,12 +1896,15 @@ static unsigned long calculate_alignment
* specified alignment though. If that is greater
* then use it.
*/
- if ((flags & SLAB_HWCACHE_ALIGN) &&
- size > cache_line_size() / 2)
- return max_t(unsigned long, align, cache_line_size());
+ if (flags & SLAB_HWCACHE_ALIGN) {
+ unsigned long ralign = cache_line_size();
+ while (size <= ralign / 2)
+ ralign /= 2;
+ align = max(align, ralign);
+ }

if (align < ARCH_SLAB_MINALIGN)
- return ARCH_SLAB_MINALIGN;
+ align = ARCH_SLAB_MINALIGN;

return ALIGN(align, sizeof(void *));
}