From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f48.google.com (mail-wm0-f48.google.com [74.125.82.48]) by kanga.kvack.org (Postfix) with ESMTP id 96D366B0009 for ; Fri, 29 Jan 2016 10:23:10 -0500 (EST) Received: by mail-wm0-f48.google.com with SMTP id r129so73149622wmr.0 for ; Fri, 29 Jan 2016 07:23:10 -0800 (PST) Received: from mail-wm0-f68.google.com (mail-wm0-f68.google.com. [74.125.82.68]) by mx.google.com with ESMTPS id i187si11615334wma.47.2016.01.29.07.23.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 Jan 2016 07:23:09 -0800 (PST) Received: by mail-wm0-f68.google.com with SMTP id r129so10483596wmr.0 for ; Fri, 29 Jan 2016 07:23:09 -0800 (PST) Date: Fri, 29 Jan 2016 16:23:08 +0100 From: Michal Hocko Subject: Re: [PATCH 4/3] mm, oom: drop the last allocation attempt before out_of_memory Message-ID: <20160129152307.GF32174@dhcp22.suse.cz> References: <1450203586-10959-1-git-send-email-mhocko@kernel.org> <1454013603-3682-1-git-send-email-mhocko@kernel.org> <20160128213634.GA4903@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Johannes Weiner , Andrew Morton , Linus Torvalds , Mel Gorman , Tetsuo Handa , Hillf Danton , KAMEZAWA Hiroyuki , linux-mm@kvack.org, LKML On Thu 28-01-16 15:19:08, David Rientjes wrote: > On Thu, 28 Jan 2016, Johannes Weiner wrote: > > > The check has to happen while holding the OOM lock, otherwise we'll > > end up killing much more than necessary when there are many racing > > allocations. > > > > Right, we need to try with ALLOC_WMARK_HIGH after oom_lock has been > acquired. > > The situation is still somewhat fragile, however, but I think it's > tangential to this patch series. If the ALLOC_WMARK_HIGH allocation fails > because an oom victim hasn't freed its memory yet, and then the TIF_MEMDIE > thread isn't visible during the oom killer's tasklist scan because it has > exited, we still end up killing more than we should. The likelihood of > this happening grows with the length of the tasklist. Yes exactly the point I made in the original thread which brought the question about ALLOC_WMARK_HIGH originally. The race window after the last attempt is much larger than between the last wmark check and the attempt. > Perhaps we should try testing watermarks after a victim has been selected > and immediately before killing? (Aside: we actually carry an internal > patch to test mem_cgroup_margin() in the memcg oom path after selecting a > victim because we have been hit with this before in the memcg path.) > > I would think that retrying with ALLOC_WMARK_HIGH would be enough memory > to deem that we aren't going to immediately reenter an oom condition so > the deferred killing is a waste of time. > > The downside is how sloppy this would be because it's blurring the line > between oom killer and page allocator. We'd need the oom killer to return > the selected victim to the page allocator, try the allocation, and then > call oom_kill_process() if necessary. Yes the layer violation is definitely not nice. -- Michal Hocko SUSE Labs -- 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