From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f46.google.com (mail-pa0-f46.google.com [209.85.220.46]) by kanga.kvack.org (Postfix) with ESMTP id DC49E828DF for ; Wed, 17 Feb 2016 15:56:05 -0500 (EST) Received: by mail-pa0-f46.google.com with SMTP id fl4so17403343pad.0 for ; Wed, 17 Feb 2016 12:56:05 -0800 (PST) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [2001:e42:101:1:202:181:97:72]) by mx.google.com with ESMTPS id l62si4129033pfi.125.2016.02.17.12.56.04 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 17 Feb 2016 12:56:04 -0800 (PST) Subject: Re: [PATCH 1/6] mm,oom: exclude TIF_MEMDIE processes from candidates. From: Tetsuo Handa References: <201602171928.GDE00540.SLJMOFFQOHtFVO@I-love.SAKURA.ne.jp> <201602171929.IFG12927.OVFJOQHOSMtFFL@I-love.SAKURA.ne.jp> <20160217124100.GE29196@dhcp22.suse.cz> <201602180140.IHH21322.OSJFHOMtFFOQVL@I-love.SAKURA.ne.jp> <20160217173317.GA29370@dhcp22.suse.cz> In-Reply-To: <20160217173317.GA29370@dhcp22.suse.cz> Message-Id: <201602180555.EGB24050.HtJFSOLOFFVQMO@I-love.SAKURA.ne.jp> Date: Thu, 18 Feb 2016 05:55:50 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@kernel.org Cc: akpm@linux-foundation.org, rientjes@google.com, mgorman@suse.de, oleg@redhat.com, torvalds@linux-foundation.org, hughd@google.com, andrea@kernel.org, riel@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Michal Hocko wrote: > > From 4d305f92e2527b6d86cd366952d598f9e95f095b Mon Sep 17 00:00:00 2001 > > From: Tetsuo Handa > > Date: Thu, 18 Feb 2016 01:16:54 +0900 > > Subject: [PATCH v2] mm,oom: exclude TIF_MEMDIE processes from candidates. > > > > It is possible that a TIF_MEMDIE thread gets stuck at > > down_read(&mm->mmap_sem) in exit_mm() called from do_exit() due to > > one of !TIF_MEMDIE threads doing a GFP_KERNEL allocation between > > down_write(&mm->mmap_sem) and up_write(&mm->mmap_sem) (e.g. mmap()). > > In that case, we need to use SysRq-f (manual invocation of the OOM > > killer) for making progress. > > > > However, it is possible that the OOM killer chooses the same OOM victim > > forever which already has TIF_MEMDIE. This is effectively disabling > > SysRq-f. This patch excludes processes which has a TIF_MEMDIE thread > > from OOM victim candidates. > > > > Signed-off-by: Tetsuo Handa > > --- > > mm/oom_kill.c | 21 ++++++++++++++++++++- > > 1 file changed, 20 insertions(+), 1 deletion(-) > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index 6e6abaf..f6f6b47 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -268,6 +268,21 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc, > > } > > #endif > > > > +/* > > + * To determine whether a task is an OOM victim, we examine all the task's > > + * threads: if one of those has TIF_MEMDIE then the task is an OOM victim. > > + */ > > +static bool is_oom_victim(struct task_struct *p) > > +{ > > + struct task_struct *t; > > + > > + for_each_thread(p, t) { > > + if (test_tsk_thread_flag(t, TIF_MEMDIE)) > > + return true; > > + } > > + return false; > > +} > > + > > enum oom_scan_t oom_scan_process_thread(struct oom_control *oc, > > struct task_struct *task, unsigned long totalpages) > > { > > @@ -278,9 +293,11 @@ 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. > > */ > > - if (test_tsk_thread_flag(task, TIF_MEMDIE)) { > > + if (is_oom_victim(task)) { > > This will make the scanning much more time consuming (you will check > all the threads in the same thread group for each scanned thread!). I > do not think this is acceptable and it is not really needed for the > !is_sysrq_oom because we are scanning all the threads anyway. > Yes, I know. What looks complicating to me is that select_bad_process() uses for_each_process_thread() when has_intersects_mems_allowed() and task_in_mem_cgroup() are using for_each_thread(). Can't we change select_bad_process() to use for_each_process() ? What are cases where for_each_process_thread() makes difference from for_each_process() ? > Regarding the is_sysrq_oom case we might indeed select a thread > which doesn't have TIF_MEMDIE but it has been already (group) killed > but an attempt to catch that case is exactly what has been Nacked > previously when I tried to achieve the same thing and had TIF_MEMDIE || > fatal_signal_pending check > (http://lkml.kernel.org/r/alpine.DEB.2.10.1601121639450.28831@chino.kir.corp.google.com). > This change will basically achieve the same (just in much more expansive > way) so I am not sure it overcomes the previous feedback. > > > if (!is_sysrq_oom(oc)) > > return OOM_SCAN_ABORT; > > + else > > + return OOM_SCAN_CONTINUE; > > } > > if (!task->mm || task->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) > > return OOM_SCAN_CONTINUE; > > @@ -711,6 +728,8 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, > > > > if (process_shares_mm(child, p->mm)) > > continue; > > + if (is_oom_victim(child)) > > + continue; > > /* > > * oom_badness() returns 0 if the thread is unkillable > > */ > > -- > > 1.8.3.1 > > -- > 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