From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758645Ab1LODKX (ORCPT ); Wed, 14 Dec 2011 22:10:23 -0500 Received: from mail-gy0-f174.google.com ([209.85.160.174]:43727 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755964Ab1LODKW (ORCPT ); Wed, 14 Dec 2011 22:10:22 -0500 Date: Wed, 14 Dec 2011 19:10:19 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Pekka Enberg cc: Christoph Lameter , Eric Dumazet , linux-kernel@vger.kernel.org Subject: Re: Switch per cpu partial page support off for debugging In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 12 Dec 2011, Pekka Enberg wrote: > > Eric saw an issue with accounting of slabs during validation. Its not > > possible to determine accurately how many per cpu partial slabs exist at > > any time so this switches off per cpu partial pages during debug. > > > > Subject: Switch per cpu partial page support off for debugging > > > > Otherwise we have accounting issues. > > > > Signed-off-by: Christoph Lameter > > > > > > --- > > mm/slub.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > Index: linux-2.6/mm/slub.c > > =================================================================== > > --- linux-2.6.orig/mm/slub.c 2011-11-22 11:57:21.000000000 -0600 > > +++ linux-2.6/mm/slub.c 2011-11-22 11:57:55.000000000 -0600 > > @@ -3027,7 +3027,9 @@ static int kmem_cache_open(struct kmem_c > > * per node list when we run out of per cpu objects. We only fetch > > 50% > > * to keep some capacity around for frees. > > */ > > - if (s->size >= PAGE_SIZE) > > + if (kmem_cache_debug(s)) > > + s->cpu_partial = 0; > > + else if (s->size >= PAGE_SIZE) > > s->cpu_partial = 2; > > else if (s->size >= 1024) > > s->cpu_partial = 6; I think this deserves a comment since it's not clear why it's being done neither in the code or by the changelog. Also, you'd want a check for kmem_cache_debug() when storing to /sys/kernel/slab/cache/cpu_partial as well, otherwise this could easily be broken from userspace again. (It also seems like Documentation/ABI/testing/sysfs-kernel-slab got left out of an update when that was added, too.)