From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id A98BB900137 for ; Mon, 29 Aug 2011 21:51:56 -0400 (EDT) Subject: [patch 1/2]slub: add slab with one free object to partial list tail - v2 From: Shaohua Li Content-Type: text/plain; charset="UTF-8" Date: Tue, 30 Aug 2011 09:54:01 +0800 Message-ID: <1314669241.29510.47.camel@sli10-conroe> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Christoph Lameter , "penberg@kernel.org" , "Shi, Alex" , "Chen, Tim C" , linux-mm The slab has just one free object, adding it to partial list head doesn't make sense. And it can cause lock contentation. For example, 1. CPU takes the slab from partial list 2. fetch an object 3. switch to another slab 4. free an object, then the slab is added to partial list again In this way n->list_lock will be heavily contended. In fact, Alex had a hackbench regression. 3.1-rc1 performance drops about 70% against 3.0. This patch fixes it. Thanks Alex to bisect the issue to be a slub regression and collect perf data. Add comments in the code as suggested by Alex. Reported-by: Alex Shi Signed-off-by: Shaohua Li Signed-off-by: Shaohua Li Acked-by: Christoph Lameter --- mm/slub.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) Index: linux/mm/slub.c =================================================================== --- linux.orig/mm/slub.c 2011-08-24 08:59:06.000000000 +0800 +++ linux/mm/slub.c 2011-08-30 09:45:03.000000000 +0800 @@ -2377,7 +2377,12 @@ static void __slab_free(struct kmem_cach */ if (unlikely(!prior)) { remove_full(s, page); - add_partial(n, page, 0); + /* + * The slab has just one free object, add it to the + * partial list tail so it will not be used + * immediately. + */ + add_partial(n, page, 1); stat(s, FREE_ADD_PARTIAL); } } -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org