From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f173.google.com (mail-io0-f173.google.com [209.85.223.173]) by kanga.kvack.org (Postfix) with ESMTP id 688A06B007E for ; Tue, 29 Mar 2016 09:45:45 -0400 (EDT) Received: by mail-io0-f173.google.com with SMTP id e3so22115734ioa.1 for ; Tue, 29 Mar 2016 06:45:45 -0700 (PDT) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [2001:e42:101:1:202:181:97:72]) by mx.google.com with ESMTPS id t37si28783729ioi.205.2016.03.29.06.45.44 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 29 Mar 2016 06:45:44 -0700 (PDT) Subject: Re: [RFC PATCH] mm, oom: move GFP_NOFS check to out_of_memory From: Tetsuo Handa References: <1459258055-1173-1-git-send-email-mhocko@kernel.org> In-Reply-To: <1459258055-1173-1-git-send-email-mhocko@kernel.org> Message-Id: <201603292245.AAC12437.JFLMQVtSOHFFOO@I-love.SAKURA.ne.jp> Date: Tue, 29 Mar 2016 22:45:40 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@kernel.org, linux-mm@kvack.org Cc: rientjes@google.com, hannes@cmpxchg.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, mhocko@suse.com Michal Hocko wrote: > From: Michal Hocko > > __alloc_pages_may_oom is the central place to decide when the > out_of_memory should be invoked. This is a good approach for most checks > there because they are page allocator specific and the allocation fails > right after. > > The notable exception is GFP_NOFS context which is faking > did_some_progress and keep the page allocator looping even though there > couldn't have been any progress from the OOM killer. This patch doesn't > change this behavior because we are not ready to allow those allocation > requests to fail yet. Instead __GFP_FS check is moved down to > out_of_memory and prevent from OOM victim selection there. There are > two reasons for that > - OOM notifiers might release some memory even from this context > as none of the registered notifier seems to be FS related > - this might help a dying thread to get an access to memory > reserves and move on which will make the behavior more > consistent with the case when the task gets killed from a > different context. Allowing !__GFP_FS allocations to get TIF_MEMDIE by calling the shortcuts in out_of_memory() would be fine. But I don't like the direction you want to go. I don't like failing !__GFP_FS allocations without selecting OOM victim ( http://lkml.kernel.org/r/201603252054.ADH30264.OJQFFLMOHFSOVt@I-love.SAKURA.ne.jp ). Also, I suggested removing all shortcuts by setting TIF_MEMDIE from oom_kill_process() ( http://lkml.kernel.org/r/1458529634-5951-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp ). > > Keep a comment in __alloc_pages_may_oom to make sure we do not forget > how GFP_NOFS is special and that we really want to do something about > it. > > Signed-off-by: Michal Hocko > --- > > Hi, > I am sending this as an RFC now even though I think this makes more > sense than what we have right now. Maybe there are some side effects > I do not see, though. A more tricky part is the OOM notifier part > becasue future notifiers might decide to depend on the FS and we can > lockup. Is this something to worry about, though? Would such a notifier > be correct at all? I would call it broken as it would put OOM killer out > of the way on the contended system which is a plain bug IMHO. > > If this looks like a reasonable approach I would go on think about how > we can extend this for the oom_reaper and queue the current thread for > the reaper to free some of the memory. > > Any thoughts -- 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/ . Don't email: email@kvack.org