From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756951AbZBMJrX (ORCPT ); Fri, 13 Feb 2009 04:47:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751460AbZBMJrN (ORCPT ); Fri, 13 Feb 2009 04:47:13 -0500 Received: from eu1sys200aog119.obsmtp.com ([207.126.144.147]:40239 "EHLO eu1sys200aog119.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751013AbZBMJrL (ORCPT ); Fri, 13 Feb 2009 04:47:11 -0500 Message-ID: <49954F9A.5020801@st.com> Date: Fri, 13 Feb 2009 11:46:50 +0100 From: Giuseppe CAVALLARO User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Pekka Enberg Cc: Paul Mundt , linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, linux-mm@vger.kernel.org, Christoph Lameter Subject: Re: [PATCH] slab: fix slab flags for archs use alignment larger 64-bit References: <1234461073-23281-1-git-send-email-peppe.cavallaro@st.com> <20090212185640.GA6111@linux-sh.org> <499544AD.3030804@st.com> <84144f020902130122y471dd92em4a72de43a0cfc681@mail.gmail.com> In-Reply-To: <84144f020902130122y471dd92em4a72de43a0cfc681@mail.gmail.com> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Pekka, thanks for your prompt feedback. Feel free to ask again if you need some other information. Peppe Kernel 2.6.23.17 ============================================= 1) LOG with my patch: root@linux:~# cat /proc/meminfo | grep Slab Slab: 2612 kB root@linux:~# cat /proc/slab_allocators rpc_buffers: 8 mempool_alloc_slab+0x10/0x1c rpc_tasks: 11 mempool_alloc_slab+0x10/0x1c rpc_inode_cache: 10 rpc_alloc_inode+0x10/0x2c ... anon_vma: 62 anon_vma_prepare+0x38/0xd4 pid: 20 alloc_pid+0x1e/0x2cc size-2048: 1 tty_write+0xac/0x1d8 size-2048: 1 alloc_netdev_mq+0x40/0xbc ... ============================================= 2) LOG without my patch: root@linux:~# cat /proc/meminfo | grep Slab Slab: 2504 kB root@linux:~# cat /proc/slab_allocators rpc_buffers: 8 mempool_alloc_slab+0x10/0x1c rpc_tasks: 11 mempool_alloc_slab+0x10/0x1c rpc_inode_cache: 10 rpc_alloc_inode+0x10/0x2c ... pid: 20 alloc_pid+0x1e/0x2cc Pekka Enberg wrote: > Hi Giuseppe, > > On Fri, Feb 13, 2009 at 12:00 PM, Giuseppe CAVALLARO > wrote: > >> IIUC, and as you explained above, ralign is already set to the cache >> line size by the following code: >> ... >> /* 3) caller mandated alignment */ >> if (ralign < align) >> ralign = align; >> >> Then, there is following check: >> ... >> /* disable debug if necessary */ >> if (ralign > _alignof__(unsigned long long)) >> flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); >> >> In my point of view, just this check appears "incoherent" (please, note >> I'm not familiar with the slab internals). >> It always makes sense in case of x86 where ARCH_KMALLOC_MINALIGN is >> defined as: __alignof__(unsigned long long) as well. >> > > The code is indeed quite cryptic but I don't think the above statement > is correct. Both SLAB_RED_ZONE and SLAB_STORE_USER add padding in > front of an object and the maximum size of that padding is 2 * > sizeof(unsigned long long). That's why we check for > __alignof__(unsigned long) there to make sure the object can begin > immediately after the padding added for red-zone and user pointer. > > On Fri, Feb 13, 2009 at 12:00 PM, Giuseppe CAVALLARO > wrote: > >> In case of sh, we always disable debug for 32 aligned objects. As side >> effect, within the leaks_show function we immediately exit for them. >> Indeed, after applying the patch, I attached, I was able to find size-X >> fields within the slab_allocators proc entry. >> > > That sounds unfortunate. Can you post > > cat /proc/meminfo | grep Slab > > results on sh without and with your patch? Bumping the limit up to > ARCH_KMALLOC_MINALIGN does make sense but we'd need to know what kind > of problems it might cause. > > Pekka > >