From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753411AbcGSMFp (ORCPT ); Tue, 19 Jul 2016 08:05:45 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:36719 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752386AbcGSMFm (ORCPT ); Tue, 19 Jul 2016 08:05:42 -0400 Date: Tue, 19 Jul 2016 14:05:39 +0200 From: Michal Hocko To: linux-mm@kvack.org Cc: Tetsuo Handa , David Rientjes , Oleg Nesterov , Vladimir Davydov , Andrew Morton , LKML Subject: Re: [PATCH 10/10] mm, oom: hide mm which is shared with kthread or global init Message-ID: <20160719120538.GE9490@dhcp22.suse.cz> References: <1466426628-15074-1-git-send-email-mhocko@kernel.org> <1466426628-15074-11-git-send-email-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1466426628-15074-11-git-send-email-mhocko@kernel.org> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew, On Mon 20-06-16 14:43:48, Michal Hocko wrote: > From: Michal Hocko > > The only case where the oom_reaper is not triggered for the oom victim > is when it shares the memory with a kernel thread (aka use_mm) or with > the global init. After "mm, oom: skip vforked tasks from being selected" > the victim cannot be a vforked task of the global init so we are left > with clone(CLONE_VM) (without CLONE_SIGHAND). use_mm() users are quite > rare as well. > > In order to guarantee a forward progress for the OOM killer make > sure that this really rare cases will not get into the way and hide > the mm from the oom killer by setting MMF_OOM_REAPED flag for it. > oom_scan_process_thread will ignore any TIF_MEMDIE task if it has > MMF_OOM_REAPED flag set to catch these oom victims. > > After this patch we should guarantee a forward progress for the OOM > killer even when the selected victim is sharing memory with a kernel > thread or global init. Could you replace the last two paragraphs with the following. Tetsuo didn't like the guarantee mentioned there because that is a too strong statement as find_lock_task_mm might not find any mm and so we still could end up looping on the oom victim if it gets stuck somewhere in __mmput. This particular patch didn't aim at closing that case. Plugging that hole is planned later after the next upcoming merge window closes. " In order to help a forward progress for the OOM killer, make sure that this really rare cases will not get into the way and hide the mm from the oom killer by setting MMF_OOM_REAPED flag for it. oom_scan_process_thread will ignore any TIF_MEMDIE task if it has MMF_OOM_REAPED flag set to catch these oom victims. After this patch we should guarantee a forward progress for the OOM killer even when the selected victim is sharing memory with a kernel thread or global init as long as the victims mm is still alive. " > > Changes since v1 > - do not exit_oom_victim because oom_scan_process_thread will handle > those which couldn't terminate in time. exit_oom_victim is not safe > wrt. oom_disable synchronization. > > Acked-by: Oleg Nesterov > Signed-off-by: Michal Hocko > --- > mm/oom_kill.c | 25 +++++++++++++++++++++---- > 1 file changed, 21 insertions(+), 4 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index bfddc93ccd34..4c21f744daa6 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -283,10 +283,22 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc, > > /* > * This task already has access to memory reserves and is being killed. > - * Don't allow any other task to have access to the reserves. > + * Don't allow any other task to have access to the reserves unless > + * the task has MMF_OOM_REAPED because chances that it would release > + * any memory is quite low. > */ > - if (!is_sysrq_oom(oc) && atomic_read(&task->signal->oom_victims)) > - return OOM_SCAN_ABORT; > + if (!is_sysrq_oom(oc) && atomic_read(&task->signal->oom_victims)) { > + struct task_struct *p = find_lock_task_mm(task); > + enum oom_scan_t ret = OOM_SCAN_ABORT; > + > + if (p) { > + if (test_bit(MMF_OOM_REAPED, &p->mm->flags)) > + ret = OOM_SCAN_CONTINUE; > + task_unlock(p); > + } > + > + return ret; > + } > > /* > * If task is allocating a lot of memory and has been marked to be > @@ -913,9 +925,14 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, > /* > * We cannot use oom_reaper for the mm shared by this > * process because it wouldn't get killed and so the > - * memory might be still used. > + * memory might be still used. Hide the mm from the oom > + * killer to guarantee OOM forward progress. > */ > can_oom_reap = false; > + set_bit(MMF_OOM_REAPED, &mm->flags); > + pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n", > + task_pid_nr(victim), victim->comm, > + task_pid_nr(p), p->comm); > continue; > } > do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true); > -- > 2.8.1 > > -- > 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 -- Michal Hocko SUSE Labs