tree 5856978e32c675393bc2cb97e3647fc91e27f3bb
parent e1cca7e8d484390169777b423a7fe46c7021fec1
author Matthew Wilcox <matthew@wil.cx> 1196363113 -0700
committer Linus Torvalds <torvalds@woody.linux-foundation.org> 1196438885 -0800

Fix kmem_cache_free performance regression in slab

The database performance group have found that half the cycles spent
in kmem_cache_free are spent in this one call to BUG_ON.  Moving it
into the CONFIG_SLAB_DEBUG-only function cache_free_debugcheck() is a
performance win of almost 0.5% on their particular benchmark.

The call was added as part of commit ddc2e812d592457747c4367fb73edcaa8e1e49ff
with the comment that "overhead should be minimal".  It may have been
minimal at the time, but it isn't now.

[ Quoth Pekka Enberg: "I don't think the BUG_ON per se caused the
  performance regression but rather the virt_to_head_page() changes to
  virt_to_cache() that were added later." ]

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Acked-by: Pekka J Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>