From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752414AbdFONWH (ORCPT ); Thu, 15 Jun 2017 09:22:07 -0400 Received: from mx2.suse.de ([195.135.220.15]:41836 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752311AbdFONWG (ORCPT ); Thu, 15 Jun 2017 09:22:06 -0400 Date: Thu, 15 Jun 2017 15:22:03 +0200 From: Michal Hocko To: Tetsuo Handa Cc: rientjes@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch] mm, oom: prevent additional oom kills before memory is freed Message-ID: <20170615132203.GM1486@dhcp22.suse.cz> References: <201706151953.HFH78657.tFFLOOOQHSMVFJ@I-love.SAKURA.ne.jp> <20170615110119.GI1486@dhcp22.suse.cz> <201706152032.BFE21313.MSHQOtLVFFJOOF@I-love.SAKURA.ne.jp> <20170615120335.GJ1486@dhcp22.suse.cz> <20170615121315.GK1486@dhcp22.suse.cz> <201706152201.CAB48456.FtHOJMFOVLSFQO@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201706152201.CAB48456.FtHOJMFOVLSFQO@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 15-06-17 22:01:33, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Thu 15-06-17 14:03:35, Michal Hocko wrote: > > > On Thu 15-06-17 20:32:39, Tetsuo Handa wrote: > > > > @@ -556,25 +553,21 @@ static void oom_reap_task(struct task_struct *tsk) > > > > struct mm_struct *mm = tsk->signal->oom_mm; > > > > > > > > /* Retry the down_read_trylock(mmap_sem) a few times */ > > > > - while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm)) > > > > + while (__oom_reap_task_mm(tsk, mm), !test_bit(MMF_OOM_SKIP, &mm->flags) > > > > + && attempts++ < MAX_OOM_REAP_RETRIES) > > > > schedule_timeout_idle(HZ/10); > > > > > > > > - if (attempts <= MAX_OOM_REAP_RETRIES) > > > > - goto done; > > > > - > > > > - > > > > - pr_info("oom_reaper: unable to reap pid:%d (%s)\n", > > > > - task_pid_nr(tsk), tsk->comm); > > > > - debug_show_all_locks(); > > > > - > > > > -done: > > > > - tsk->oom_reaper_list = NULL; > > > > - > > > > /* > > > > * Hide this mm from OOM killer because it has been either reaped or > > > > * somebody can't call up_write(mmap_sem). > > > > */ > > > > - set_bit(MMF_OOM_SKIP, &mm->flags); > > > > + if (!test_and_set_bit(MMF_OOM_SKIP, &mm->flags)) { > > > > + pr_info("oom_reaper: unable to reap pid:%d (%s)\n", > > > > + task_pid_nr(tsk), tsk->comm); > > > > + debug_show_all_locks(); > > > > + } > > > > + > > > > > > How does this _solve_ anything? Why would you even retry when you > > > _know_ that the reference count dropped to zero. It will never > > > increment. So the above is basically just schedule_timeout_idle(HZ/10) * > > > MAX_OOM_REAP_RETRIES before we set MMF_OOM_SKIP. > > If the OOM reaper knows that mm->users == 0, it gives __mmput() some time > to "complete exit_mmap() etc. and set MMF_OOM_SKIP". If __mmput() released > some memory, subsequent OOM killer invocation is automatically avoided. > If __mmput() did not release some memory, let the OOM killer invoke again. > > > > > Just to make myself more clear. The above assumes that the victim hasn't > > passed exit_mmap and MMF_OOM_SKIP in __mmput. Which is the case we want to > > address here. > > David is trying to avoid setting MMF_OOM_SKIP when the OOM reaper found that > mm->users == 0. But we must not wait forever because __mmput() might fail to > release some memory immediately. If __mmput() did not release some memory within > schedule_timeout_idle(HZ/10) * MAX_OOM_REAP_RETRIES sleep, let the OOM killer > invoke again. So, this is the case we want to address here, isn't it? And we are back with a timeout based approach... Sigh. Just imagine that you have a really large process which will take some time to tear down. While it frees memory that might be in a different oom domain. Now you pretend to keep retrying and eventually give up to allow a new oom victim from that oom domain. If we want to handle oom victims with mm_users == 0 then let's do it properly, please. -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 934DE6B0279 for ; Thu, 15 Jun 2017 09:22:07 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id v60so3583819wrc.7 for ; Thu, 15 Jun 2017 06:22:07 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id j199si136023wmd.133.2017.06.15.06.22.05 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 15 Jun 2017 06:22:06 -0700 (PDT) Date: Thu, 15 Jun 2017 15:22:03 +0200 From: Michal Hocko Subject: Re: [patch] mm, oom: prevent additional oom kills before memory is freed Message-ID: <20170615132203.GM1486@dhcp22.suse.cz> References: <201706151953.HFH78657.tFFLOOOQHSMVFJ@I-love.SAKURA.ne.jp> <20170615110119.GI1486@dhcp22.suse.cz> <201706152032.BFE21313.MSHQOtLVFFJOOF@I-love.SAKURA.ne.jp> <20170615120335.GJ1486@dhcp22.suse.cz> <20170615121315.GK1486@dhcp22.suse.cz> <201706152201.CAB48456.FtHOJMFOVLSFQO@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201706152201.CAB48456.FtHOJMFOVLSFQO@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: rientjes@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu 15-06-17 22:01:33, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Thu 15-06-17 14:03:35, Michal Hocko wrote: > > > On Thu 15-06-17 20:32:39, Tetsuo Handa wrote: > > > > @@ -556,25 +553,21 @@ static void oom_reap_task(struct task_struct *tsk) > > > > struct mm_struct *mm = tsk->signal->oom_mm; > > > > > > > > /* Retry the down_read_trylock(mmap_sem) a few times */ > > > > - while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm)) > > > > + while (__oom_reap_task_mm(tsk, mm), !test_bit(MMF_OOM_SKIP, &mm->flags) > > > > + && attempts++ < MAX_OOM_REAP_RETRIES) > > > > schedule_timeout_idle(HZ/10); > > > > > > > > - if (attempts <= MAX_OOM_REAP_RETRIES) > > > > - goto done; > > > > - > > > > - > > > > - pr_info("oom_reaper: unable to reap pid:%d (%s)\n", > > > > - task_pid_nr(tsk), tsk->comm); > > > > - debug_show_all_locks(); > > > > - > > > > -done: > > > > - tsk->oom_reaper_list = NULL; > > > > - > > > > /* > > > > * Hide this mm from OOM killer because it has been either reaped or > > > > * somebody can't call up_write(mmap_sem). > > > > */ > > > > - set_bit(MMF_OOM_SKIP, &mm->flags); > > > > + if (!test_and_set_bit(MMF_OOM_SKIP, &mm->flags)) { > > > > + pr_info("oom_reaper: unable to reap pid:%d (%s)\n", > > > > + task_pid_nr(tsk), tsk->comm); > > > > + debug_show_all_locks(); > > > > + } > > > > + > > > > > > How does this _solve_ anything? Why would you even retry when you > > > _know_ that the reference count dropped to zero. It will never > > > increment. So the above is basically just schedule_timeout_idle(HZ/10) * > > > MAX_OOM_REAP_RETRIES before we set MMF_OOM_SKIP. > > If the OOM reaper knows that mm->users == 0, it gives __mmput() some time > to "complete exit_mmap() etc. and set MMF_OOM_SKIP". If __mmput() released > some memory, subsequent OOM killer invocation is automatically avoided. > If __mmput() did not release some memory, let the OOM killer invoke again. > > > > > Just to make myself more clear. The above assumes that the victim hasn't > > passed exit_mmap and MMF_OOM_SKIP in __mmput. Which is the case we want to > > address here. > > David is trying to avoid setting MMF_OOM_SKIP when the OOM reaper found that > mm->users == 0. But we must not wait forever because __mmput() might fail to > release some memory immediately. If __mmput() did not release some memory within > schedule_timeout_idle(HZ/10) * MAX_OOM_REAP_RETRIES sleep, let the OOM killer > invoke again. So, this is the case we want to address here, isn't it? And we are back with a timeout based approach... Sigh. Just imagine that you have a really large process which will take some time to tear down. While it frees memory that might be in a different oom domain. Now you pretend to keep retrying and eventually give up to allow a new oom victim from that oom domain. If we want to handle oom victims with mm_users == 0 then let's do it properly, please. -- Michal Hocko SUSE Labs -- 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