From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754119AbcEZOaL (ORCPT ); Thu, 26 May 2016 10:30:11 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:57147 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753813AbcEZOaJ (ORCPT ); Thu, 26 May 2016 10:30:09 -0400 To: mhocko@kernel.org, linux-mm@kvack.org Cc: rientjes@google.com, oleg@redhat.com, vdavydov@parallels.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, mhocko@suse.com Subject: Re: [PATCH 1/6] mm, oom: do not loop over all tasks if there are no external tasks sharing mm From: Tetsuo Handa References: <1464266415-15558-1-git-send-email-mhocko@kernel.org> <1464266415-15558-2-git-send-email-mhocko@kernel.org> In-Reply-To: <1464266415-15558-2-git-send-email-mhocko@kernel.org> Message-Id: <201605262330.EEB52182.OtMFOJHFLOSFVQ@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Thu, 26 May 2016 23:30:06 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michal Hocko wrote: > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 5bb2f7698ad7..0e33e912f7e4 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -820,6 +820,13 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, > task_unlock(victim); > > /* > + * skip expensive iterations over all tasks if we know that there > + * are no users outside of threads in the same thread group > + */ > + if (atomic_read(&mm->mm_users) <= get_nr_threads(victim)) > + goto oom_reap; Is this really safe? Isn't it possible that victim thread's thread group has more than atomic_read(&mm->mm_users) threads which are past exit_mm() and blocked at exit_task_work() which are before __exit_signal() from release_task() from exit_notify()? > + > + /* > * Kill all user processes sharing victim->mm in other thread groups, if > * any. They don't get access to memory reserves, though, to avoid > * depletion of all memory. This prevents mm->mmap_sem livelock when an