From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f181.google.com (mail-ob0-f181.google.com [209.85.214.181]) by kanga.kvack.org (Postfix) with ESMTP id 0FFC4828DF for ; Thu, 14 Jan 2016 05:26:35 -0500 (EST) Received: by mail-ob0-f181.google.com with SMTP id vt7so79370445obb.1 for ; Thu, 14 Jan 2016 02:26:35 -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 x12si6433046oix.96.2016.01.14.02.26.33 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 14 Jan 2016 02:26:33 -0800 (PST) Subject: Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates. From: Tetsuo Handa References: <20160107154436.GO27868@dhcp22.suse.cz> <201601081909.CDJ52685.HLFOFJFOQMVOtS@I-love.SAKURA.ne.jp> <201601131952.HAJ18298.OQLtSOFOFFMVJH@I-love.SAKURA.ne.jp> In-Reply-To: Message-Id: <201601141926.JHG56933.OFFHOFOLQMtJSV@I-love.SAKURA.ne.jp> Date: Thu, 14 Jan 2016 19:26:19 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: rientjes@google.com Cc: mhocko@kernel.org, hannes@cmpxchg.org, 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 David Rientjes wrote: > On Wed, 13 Jan 2016, Tetsuo Handa wrote: > > > David Rientjes wrote: > > > > @@ -171,7 +195,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg, > > > > if (oom_unkillable_task(p, memcg, nodemask)) > > > > return 0; > > > > > > > > - p = find_lock_task_mm(p); > > > > + p = find_lock_non_victim_task_mm(p); > > > > if (!p) > > > > return 0; > > > > > > > > > > I understand how this may make your test case pass, but I simply don't > > > understand how this could possibly be the correct thing to do. This would > > > cause oom_badness() to return 0 for any process where a thread has > > > TIF_MEMDIE set. If the oom killer is called from the page allocator, > > > kills a thread, and it is recalled before that thread may exit, then this > > > will panic the system if there are no other eligible processes to kill. > > > > > Why? oom_badness() is called after oom_scan_process_thread() returned OOM_SCAN_OK. > > oom_scan_process_thread() returns OOM_SCAN_ABORT if a thread has TIF_MEMDIE set. > > > > oom_scan_process_thread() checks for TIF_MEMDIE on p, not on p's threads. > If one of p's threads has TIF_MEMDIE set and p does not, we actually want > to set TIF_MEMDIE for p. That's the current behavior since it will lead > to p->mm memory freeing. Your patch is excluding such processes entirely > and selecting another process to kill unnecessarily. > I think p's threads are checked by oom_scan_process_thread() for TIF_MEMDIE even if p does not have TIF_MEMDIE. What am I misunderstanding about what for_each_process_thread(g, p) is doing? #define for_each_process_thread(p, t) for_each_process(p) for_each_thread(p, t) select_bad_process() { for_each_process_thread(g, p) { oom_scan_process_thread(oc, p, totalpages)); oom_badness(p); } } -- 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