From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030453AbWGZIxq (ORCPT ); Wed, 26 Jul 2006 04:53:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030456AbWGZIxq (ORCPT ); Wed, 26 Jul 2006 04:53:46 -0400 Received: from mtagate1.de.ibm.com ([195.212.29.150]:46752 "EHLO mtagate1.de.ibm.com") by vger.kernel.org with ESMTP id S1030453AbWGZIxp (ORCPT ); Wed, 26 Jul 2006 04:53:45 -0400 Date: Wed, 26 Jul 2006 10:51:13 +0200 From: Heiko Carstens To: Christoph Lameter Cc: Andrew Morton , linux-kernel@vger.kernel.org, Pekka Enberg , linux-mm@kvack.org, Martin Schwidefsky Subject: [patch 2/2] slab: always consider arch mandated alignment Message-ID: <20060726085113.GD9592@osiris.boeblingen.de.ibm.com> References: <20060722110601.GA9572@osiris.boeblingen.de.ibm.com> <20060722162607.GA10550@osiris.ibm.com> <20060723073500.GA10556@osiris.ibm.com> <20060723162427.GA10553@osiris.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060723162427.GA10553@osiris.ibm.com> User-Agent: mutt-ng/devel-r804 (Linux) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Heiko Carstens Since ARCH_KMALLOC_MINALIGN didn't work on s390 I tried ARCH_SLAB_MINALIGN instead, just to find out that it didn't work too. In case of CONFIG_DEBUG_SLAB kmem_cache_create() creates caches with an alignment lesser than ARCH_SLAB_MINALIGN, which it shouldn't according to this comment in mm/slab.c : * Enforce a minimum alignment for all caches. * Intended for archs that get misalignment faults even for BYTES_PER_WORD * aligned buffers. Includes ARCH_KMALLOC_MINALIGN. * If possible: Do not enable this flag for CONFIG_DEBUG_SLAB, it disables * some debug features. For example the following might happen if kmem_cache_create() gets called with -- size: 64; align: 0; flags with SLAB_HWCACHE_ALIGN, SLAB_RED_ZONE and SLAB_STORE_USER set. ARCH_SLAB_MINALIGN is 8. These are the steps as numbered in kmem_cache_create() where 5) is after the "if (flags & SLAB_RED_ZONE)" statement. 1) align: 0 ralign 64 2) align: 0 ralign 64 3) align: 0 ralign 64 4) align: 64 ralign 64 5) align: 4 ralign 64 Note that in this case in step 2) the flags SLAB_RED_ZONE and SLAB_STORE_USER don't get masked out and that this causes an BYTES_PER_WORD alignment in step 5) which is lesser than ARCH_SLAB_MINALIGN. Cc: Christoph Lameter Cc: Pekka Enberg Signed-off-by: Heiko Carstens --- mm/slab.c | 3 +++ 1 files changed, 3 insertions(+) Index: linux-2.6/mm/slab.c =================================================================== --- linux-2.6.orig/mm/slab.c 2006-07-26 09:55:54.000000000 +0200 +++ linux-2.6/mm/slab.c 2006-07-26 09:57:07.000000000 +0200 @@ -2103,6 +2103,9 @@ if (ralign > BYTES_PER_WORD) flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); } + if (BYTES_PER_WORD < ARCH_SLAB_MINALIGN) + flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); + /* 3) caller mandated alignment: disables debug if necessary */ if (ralign < align) { ralign = align;