From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751065AbcA1XTM (ORCPT ); Thu, 28 Jan 2016 18:19:12 -0500 Received: from mail-pf0-f178.google.com ([209.85.192.178]:36781 "EHLO mail-pf0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750721AbcA1XTK (ORCPT ); Thu, 28 Jan 2016 18:19:10 -0500 Date: Thu, 28 Jan 2016 15:19:08 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Johannes Weiner cc: Michal Hocko , Andrew Morton , Linus Torvalds , Mel Gorman , Tetsuo Handa , Hillf Danton , KAMEZAWA Hiroyuki , linux-mm@kvack.org, LKML , Michal Hocko Subject: Re: [PATCH 4/3] mm, oom: drop the last allocation attempt before out_of_memory In-Reply-To: <20160128213634.GA4903@cmpxchg.org> Message-ID: References: <1450203586-10959-1-git-send-email-mhocko@kernel.org> <1454013603-3682-1-git-send-email-mhocko@kernel.org> <20160128213634.GA4903@cmpxchg.org> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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.