From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f172.google.com (mail-pf0-f172.google.com [209.85.192.172]) by kanga.kvack.org (Postfix) with ESMTP id 903E26B026A for ; Wed, 13 Jan 2016 05:52:24 -0500 (EST) Received: by mail-pf0-f172.google.com with SMTP id n128so79553274pfn.3 for ; Wed, 13 Jan 2016 02:52:24 -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 u16si1273128pfa.225.2016.01.13.02.52.23 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 13 Jan 2016 02:52:23 -0800 (PST) Subject: Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates. From: Tetsuo Handa References: <201601072231.DGG78695.OOFVLHJFFQOStM@I-love.SAKURA.ne.jp> <20160107145841.GN27868@dhcp22.suse.cz> <20160107154436.GO27868@dhcp22.suse.cz> <201601081909.CDJ52685.HLFOFJFOQMVOtS@I-love.SAKURA.ne.jp> In-Reply-To: Message-Id: <201601131952.HAJ18298.OQLtSOFOFFMVJH@I-love.SAKURA.ne.jp> Date: Wed, 13 Jan 2016 19:52:08 +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: > > @@ -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. If the TIF_MEMDIE thread already exited, find_lock_non_victim_task_mm() acts like find_lock_task_mm(). Otherwise, oom_scan_process_thread() acts like a blocker. -- 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