From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 29 Nov 2007 12:05:13 -0700 From: Matthew Wilcox Subject: [PATCH] Fix kmem_cache_free performance regression in slab Message-ID: <20071129190513.GD2584@parisc-linux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton , Linus Torvalds , Pekka Enberg Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: 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. Signed-off-by: Matthew Wilcox diff --git a/mm/slab.c b/mm/slab.c index cfa6be4..6e16431 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -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); -- Intel are signing my paycheques ... these opinions are still mine "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org