From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f182.google.com (mail-io0-f182.google.com [209.85.223.182]) by kanga.kvack.org (Postfix) with ESMTP id D62A16B0005 for ; Fri, 19 Feb 2016 12:34:59 -0500 (EST) Received: by mail-io0-f182.google.com with SMTP id z135so117091094iof.0 for ; Fri, 19 Feb 2016 09:34:59 -0800 (PST) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id h65si22704407ioi.100.2016.02.19.09.34.58 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 19 Feb 2016 09:34:59 -0800 (PST) Subject: Re: [PATCH] mm,oom: kill duplicated oom_unkillable_task() checks. From: Tetsuo Handa References: <1455892411-7611-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20160219151043.GI12690@dhcp22.suse.cz> <201602200101.IBE90199.OSOFMFOLVtJQHF@I-love.SAKURA.ne.jp> <20160219171533.GA23376@dhcp22.suse.cz> In-Reply-To: <20160219171533.GA23376@dhcp22.suse.cz> Message-Id: <201602200234.DGG56738.LQFMFJFtOOVSOH@I-love.SAKURA.ne.jp> Date: Sat, 20 Feb 2016 02:34:43 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@kernel.org Cc: rientjes@google.com, hannes@cmpxchg.org, vdavydov@virtuozzo.com, linux-mm@kvack.org Michal Hocko wrote: > On Sat 20-02-16 01:01:36, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > On Fri 19-02-16 23:33:31, Tetsuo Handa wrote: > > > > Currently, oom_unkillable_task() is called for twice for each thread, > > > > once at oom_scan_process_thread() and again at oom_badness(). > > > > > > > > The reason oom_scan_process_thread() needs to call oom_unkillable_task() > > > > is to skip TIF_MEMDIE test and oom_task_origin() test if that thread is > > > > not OOM-killable. > > > > > > > > But there is a problem with this ordering, for oom_task_origin() == true > > > > will unconditionally select that thread regardless of oom_score_adj. > > > > When we merge the OOM reaper, the OOM reaper will mark already reaped > > > > process as OOM-unkillable by updating oom_score_adj. In order to avoid > > > > falling into infinite loop, oom_score_adj needs to be checked before > > > > doing oom_task_origin() test. > > > > > > What would be the infinite loop? > > > > Sequence until we merge the OOM reaper: > > > > (1) select_bad_process() returns p due to oom_task_origin(p) == true. > > (2) oom_kill_process() sends SIGKILL to p and sets TIF_MEMDIE on p. > > (3) p gets stuck at down_read(&mm->mmap_sem) in exit_mm(). > > (4) The OOM killer will ignore TIF_MEMDIE on p after some timeout expires. > > (5) select_bad_process() returns p again due to oom_task_origin(p) == true && > > p->mm != NULL. > > And one more thing. The task will stop being oom_task_origin right > after it detects signal pending and retuns from try_to_unuse resp. > unmerge_and_remove_all_rmap_items. That's good. Then, we don't need to worry about oom_task_origin() case. So, the purpose of this "[PATCH] mm,oom: kill duplicated oom_unkillable_task() checks." became only to save oom_unkillable_task() call. I'm trying to update select_bad_process() to use for_each_process() rather than for_each_process_thread(). If we can do it, I think we can use is_oom_victim() and respond to your concern | This will make the scanning much more time consuming (you will check | all the threads in the same thread group for each scanned thread!). I | do not think this is acceptable and it is not really needed for the | !is_sysrq_oom because we are scanning all the threads anyway. while excluding TIF_MEMDIE processes from candidates. -- 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