From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f172.google.com (mail-ob0-f172.google.com [209.85.214.172]) by kanga.kvack.org (Postfix) with ESMTP id A5ACC828DF for ; Thu, 14 Jan 2016 06:26:44 -0500 (EST) Received: by mail-ob0-f172.google.com with SMTP id py5so112676962obc.2 for ; Thu, 14 Jan 2016 03:26:44 -0800 (PST) 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 xs11si6737592oec.89.2016.01.14.03.26.41 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 14 Jan 2016 03:26:43 -0800 (PST) Subject: Re: [PATCH] mm,oom: Re-enable OOM killer using timers. From: Tetsuo Handa References: <201601132111.GIG81705.LFOOHFOtQJSMVF@I-love.SAKURA.ne.jp> <20160113162610.GD17512@dhcp22.suse.cz> <20160113165609.GA21950@cmpxchg.org> <20160113180147.GL17512@dhcp22.suse.cz> In-Reply-To: <20160113180147.GL17512@dhcp22.suse.cz> Message-Id: <201601142026.BHI87005.FSOFJVFQMtHOOL@I-love.SAKURA.ne.jp> Date: Thu, 14 Jan 2016 20:26:29 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@kernel.org, hannes@cmpxchg.org Cc: rientjes@google.com, akpm@linux-foundation.org, mgorman@suse.de, torvalds@linux-foundation.org, oleg@redhat.com, hughd@google.com, andrea@kernel.org, riel@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Michal Hocko wrote: > I think you are missing an important point. There is _no reliable_ way > to resolve the OOM condition in general except to panic the system. Even > killing all user space tasks might not be sufficient in general because > they might be blocked by an unkillable context (e.g. kernel thread). I know. What I'm proposing is try to recover by killing more OOM-killable tasks because I think impact of crashing the kernel is larger than impact of killing all OOM-killable tasks. We should at least try OOM-kill all OOM-killable processes before crashing the kernel. Some servers take many minutes to reboot whereas restarting OOM-killed services takes only a few seconds. Also, SysRq-i is inconvenient because it kills OOM-unkillable ssh daemon process. An example is: (1) Kill a victim and start timeout counter. (2) Kill all oom_score_adj > 0 tasks when OOM condition was not solved after 5 seconds since (1). (3) Kill all oom_score_adj = 0 tasks when OOM condition was not solved after 5 seconds since (2). (4) Kill all oom_score_adj >= -500 tasks when OOM condition was not solved after 5 seconds since (3). (5) Kill all oom_score_adj >= -999 tasks when OOM condition was not solved after 5 seconds since (4). (6) Trigger kernel panic because only OOM-unkillable tasks are left when OOM condition was not solved after 5 seconds since (5). > All we can do is a best effort approach which tries to be optimized to > reduce the impact of an unexpected SIGKILL sent to a "random" task. And > this is a reasonable objective IMHO. A best effort approach which tries to be optimized to reduce the possibility of kernel panic should exist. Michal Hocko wrote: > Timeout-to-panic patches were just trying to be as simple as possible > to guarantee the predictability requirement. No other timeout based > solutions, which were proposed so far, did guarantee the same AFAIR. What did "[PATCH] mm: Introduce timeout based OOM killing" miss ( http://lkml.kernel.org/r/201505232339.DAB00557.VFFLHMSOJFOOtQ@I-love.SAKURA.ne.jp )? It provided (1) warn OOM victim not dying using memdie_task_warn_secs timeout (2) select next OOM victim using memdie_task_skip_secs timeout (3) trigger kernel panic using memdie_task_panic_secs timeout (4) warn trashing condition using memalloc_task_warn_secs timeout (5) trigger OOM killer using memalloc_task_retry_secs timeout -- 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