From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752464AbcALTwF (ORCPT ); Tue, 12 Jan 2016 14:52:05 -0500 Received: from mail-wm0-f66.google.com ([74.125.82.66]:34974 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751869AbcALTwD (ORCPT ); Tue, 12 Jan 2016 14:52:03 -0500 Date: Tue, 12 Jan 2016 20:52:00 +0100 From: Michal Hocko To: Tetsuo Handa 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 Subject: Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates. Message-ID: <20160112195200.GB4515@dhcp22.suse.cz> References: <20160107091512.GB27868@dhcp22.suse.cz> <201601072231.DGG78695.OOFVLHJFFQOStM@I-love.SAKURA.ne.jp> <20160107145841.GN27868@dhcp22.suse.cz> <201601080038.CIF04698.VFJHSOQLOFFMOt@I-love.SAKURA.ne.jp> <20160111151835.GH27317@dhcp22.suse.cz> <201601122032.FHH13586.MOQVFFOJStFHOL@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201601122032.FHH13586.MOQVFFOJStFHOL@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 12-01-16 20:32:18, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Fri 08-01-16 00:38:43, Tetsuo Handa wrote: > > > Michal Hocko wrote: > > > > @@ -333,6 +333,14 @@ static struct task_struct *select_bad_process(struct oom_control *oc, > > > > if (points == chosen_points && thread_group_leader(chosen)) > > > > continue; > > > > > > > > + /* > > > > + * If the current major task is already ooom killed and this > > > > + * is sysrq+f request then we rather choose somebody else > > > > + * because the current oom victim might be stuck. > > > > + */ > > > > + if (is_sysrq_oom(sc) && test_tsk_thread_flag(p, TIF_MEMDIE)) > > > > + continue; > > > > + > > > > chosen = p; > > > > chosen_points = points; > > > > } > > > > > > Do we want to require SysRq-f for each thread in a process? > > > If g has 1024 p, dump_tasks() will do > > > > > > pr_info("[%5d] %5d %5d %8lu %8lu %7ld %7ld %8lu %5hd %s\n", > > > > > > for 1024 times? I think one SysRq-f per one process is sufficient. > > > > I am not following you here. If we kill the process the whole process > > group (aka all threads) will get killed which ever thread we happen to > > send the sigkill to. > > Please distinguish "sending SIGKILL to a process" and "all threads in that > process terminate". I didn't say anything about termination if your read my response again. [...] > > > How can we guarantee that find_lock_task_mm() from oom_kill_process() > > > chooses !TIF_MEMDIE thread when try_to_sacrifice_child() somehow chose > > > !TIF_MEMDIE thread? I think choosing !TIF_MEMDIE thread at > > > find_lock_task_mm() is the simplest way. > > > > find_lock_task_mm chosing TIF_MEMDIE thread shouldn't change anything > > because the whole thread group will go down anyway. If you want to > > guarantee that the sysrq+f never choses a task which has a TIF_MEMDIE > > thread then we would have to check for fatal_signal_pending as well > > AFAIU. Fiddling with find find_lock_task_mm will not help you though > > unless I am missing something. > > I do want to guarantee that the SysRq-f (and timeout based next victim > selection) never chooses a process which has a TIF_MEMDIE thread. Sigh... see what I have written in the paragraph you are replying to... > I don't like current "oom: clear TIF_MEMDIE after oom_reaper managed to unmap > the address space" patch unless both "mm,oom: exclude TIF_MEMDIE processes from > candidates." patch and "mm,oom: Re-enable OOM killer using timers." Those patches are definitely not a prerequisite from the functional point of view and putting them together as a prerequisite sounds like blocking a useful feature without technical grounds to me. -- Michal Hocko SUSE Labs