Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932371AbcCKOan (ORCPT ); Fri, 11 Mar 2016 09:30:43 -0500 Received: from mail-wm0-f46.google.com ([74.125.82.46]:38489 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932197AbcCKOae (ORCPT ); Fri, 11 Mar 2016 09:30:34 -0500 Date: Fri, 11 Mar 2016 15:30:31 +0100 From: Michal Hocko To: Vladimir Davydov Cc: Andrew Morton , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: memcontrol: zap task_struct->memcg_oom_{gfp_mask,order} Message-ID: <20160311143031.GS27701@dhcp22.suse.cz> References: <1457691167-22756-1-git-send-email-vdavydov@virtuozzo.com> <20160311115450.GH27701@dhcp22.suse.cz> <20160311123900.GM1946@esperanza> <20160311125104.GM27701@dhcp22.suse.cz> <20160311134533.GN1946@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160311134533.GN1946@esperanza> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2341 Lines: 55 On Fri 11-03-16 16:45:34, Vladimir Davydov wrote: > On Fri, Mar 11, 2016 at 01:51:05PM +0100, Michal Hocko wrote: > > On Fri 11-03-16 15:39:00, Vladimir Davydov wrote: > > > On Fri, Mar 11, 2016 at 12:54:50PM +0100, Michal Hocko wrote: > > > > On Fri 11-03-16 13:12:47, Vladimir Davydov wrote: > > > > > These fields are used for dumping info about allocation that triggered > > > > > OOM. For cgroup this information doesn't make much sense, because OOM > > > > > killer is always invoked from page fault handler. > > > > > > > > The oom killer is indeed invoked in a different context but why printing > > > > the original mask and order doesn't make any sense? Doesn't it help to > > > > see that the reclaim has failed because of GFP_NOFS? > > > > > > I don't see how this can be helpful. How would you use it? > > > > If we start seeing GFP_NOFS triggered OOMs we might be enforced to > > rethink our current strategy to ignore this charge context for OOM. > > IMO the fact that a lot of OOMs are triggered by GFP_NOFS allocations > can't be a good enough reason to reconsider OOM strategy. What I meant was that the global OOM doesn't trigger OOM got !__GFP_FS while we do in the memcg charge path. > We need to > know what kind of allocation fails anyway, and the current OOM dump > gives us no clue about that. We do print gfp_mask now so we know what was the charging context. > Besides, what if OOM was triggered by GFP_NOFS by pure chance, i.e. it > would have been triggered by GFP_KERNEL if it had happened at that time? Not really. GFP_KERNEL would allow to invoke some shrinkers which are GFP_NOFS incopatible. > IMO it's just confusing. > > > > > > Wouldn't it be better to print err msg in try_charge anyway? > > > > Wouldn't that lead to excessive amount of logged messages? > > We could ratelimit these messages. Slab charge failures are already > reported to dmesg (see ___slab_alloc -> slab_out_of_memory) and nobody's > complained so far. Are there any non-slab GFP_NOFS allocations charged > to memcg? I believe there might be some coming from FS via add_to_page_cache_lru. Especially when their mapping gfp_mask clears __GFP_FS. I haven't checked the code deeper but some of those might be called from the page fault path and trigger memcg OOM. I would have to look closer. -- Michal Hocko SUSE Labs