From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751369AbeDXXIV (ORCPT ); Tue, 24 Apr 2018 19:08:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:35775 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751061AbeDXXIU (ORCPT ); Tue, 24 Apr 2018 19:08:20 -0400 Date: Tue, 24 Apr 2018 17:08:15 -0600 From: Michal Hocko To: David Rientjes Cc: Andrew Morton , Tetsuo Handa , Andrea Arcangeli , guro@fb.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch v2] mm, oom: fix concurrent munlock and oom reaperunmap Message-ID: <20180424230815.GX17484@dhcp22.suse.cz> References: <20180420124044.GA17484@dhcp22.suse.cz> <201804221248.CHE35432.FtOMOLSHOFJFVQ@I-love.SAKURA.ne.jp> <20180424130432.GB17484@dhcp22.suse.cz> <20180424201352.GV17484@dhcp22.suse.cz> <20180424203148.GW17484@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 24-04-18 14:07:52, David Rientjes wrote: > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > > My patch has passed intensive testing on both x86 and powerpc, so I'll ask > > > > > that it's pushed for 4.17-rc3. Many thanks to Tetsuo for the suggestion > > > > > on calling __oom_reap_task_mm() from exit_mmap(). > > > > > > > > Yeah, but your patch does have a problem with blockable mmu notifiers > > > > IIUC. > > > > > > What on earth are you talking about? exit_mmap() does > > > mmu_notifier_release(). There are no blockable mmu notifiers. > > > > MMF_OOM_SKIP - remember? The thing that guarantees a forward progress. > > So we cannot really depend on setting MMF_OOM_SKIP if a > > mmu_notifier_release blocks for an excessive/unbounded amount of time. > > > > If the thread is blocked in exit_mmap() because of mmu_notifier_release() > then the oom reaper will eventually grab mm->mmap_sem (nothing holding it > in exit_mmap()), return true, and oom_reap_task() will set MMF_OOM_SKIP. > This is unchanged with the patch and is a completely separate issue. I must be missing something or we are talking past each other. So let me be explicit. What does prevent the following oom_reaper exit_mmap mutex_lock(oom_lock) mutex_lock(oom_lock) __oom_reap_task_mm mmu_notifier_invalidate_range_start # blockable mmu_notifier # which takes ages to # finish or depends on # an allocation (in)directly -- Michal Hocko SUSE Labs