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Commit 80cbd911 authored by Matthew Wilcox's avatar Matthew Wilcox Committed by Linus Torvalds
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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 ddc2e812
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: default avatarMatthew Wilcox <willy@linux.intel.com>
Acked-by: default avatarPekka J Enberg <penberg@cs.helsinki.fi>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e1cca7e8

mm/slab.c

+2 −2
Original line number Diff line number Diff line
@@ -2881,6 +2881,8 @@ static void *cache_free_debugcheck(struct kmem_cache *cachep, void *objp, 
	unsigned int objnr;

	struct slab *slabp;



	BUG_ON(virt_to_cache(objp) != cachep);



	objp -= obj_offset(cachep);

	kfree_debugcheck(objp);

	page = virt_to_head_page(objp);
@@ -3759,8 +3761,6 @@ void kmem_cache_free(struct kmem_cache *cachep, void *objp) 
{

	unsigned long flags;



	BUG_ON(virt_to_cache(objp) != cachep);



	local_irq_save(flags);

	debug_check_no_locks_freed(objp, obj_size(cachep));

	__cache_free(cachep, objp);