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From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: "Arkadiusz Miśkiewicz" <a.miskiewicz@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Tejun Heo" <tj@kernel.org>,
	cgroups@vger.kernel.org, "Aleksa Sarai" <asarai@suse.de>,
	"Jay Kamat" <jgkamat@fb.com>, "Roman Gushchin" <guro@fb.com>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	linux-kernel@vger.kernel.org,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH v2] oom, oom_reaper: do not enqueue same task twice
Date: Sun, 27 Jan 2019 12:40:21 +0100
Message-ID: <20190127114021.GB18811@dhcp22.suse.cz> (raw)
In-Reply-To: <ec0d0580-a2dd-f329-9707-0cb91205a216@i-love.sakura.ne.jp>

On Sun 27-01-19 19:56:06, Tetsuo Handa wrote:
> On 2019/01/27 17:37, Michal Hocko wrote:
> > Thanks for the analysis and the patch. This should work, I believe but
> > I am not really thrilled to overload the meaning of the MMF_UNSTABLE.
> > The flag is meant to signal accessing address space is not stable and it
> > is not aimed to synchronize oom reaper with the oom path.
> > 
> > Can we make use mark_oom_victim directly? I didn't get to think that
> > through right now so I might be missing something but this should
> > prevent repeating queueing as well.
> 
> Yes, TIF_MEMDIE would work. But you are planning to remove TIF_MEMDIE. Also,
> TIF_MEMDIE can't avoid enqueuing many threads sharing mm_struct to the OOM
> reaper. There is no need to enqueue many threads sharing mm_struct because
> the OOM reaper acts on mm_struct rather than task_struct. Thus, enqueuing
> based on per mm_struct flag sounds better, but MMF_OOM_VICTIM cannot be
> set from wake_oom_reaper(victim) because victim's mm might be already inside
> exit_mmap() when wake_oom_reaper(victim) is called after task_unlock(victim).
>
> We could reintroduce MMF_OOM_KILLED in commit 855b018325737f76
> ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task")
> if you don't like overloading the meaning of the MMF_UNSTABLE. But since
> MMF_UNSTABLE is available in Linux 4.9+ kernels (which covers all LTS stable
> versions with the OOM reaper support), we can temporarily use MMF_UNSTABLE
> for ease of backporting.

I agree that a per-mm state is more optimal but I would rather fix the
issue in a clear way first and only then think about an optimization on
top. Queueing based on mark_oom_victim (whatever that uses to guarantee
the victim is marked atomically and only once) makes sense from the
conceptual point of view and it makes a lot of sense to start from
there. MMF_UNSTABLE has a completely different purpose. So unless you
see a correctness issue with that then I would rather go that way.
-- 
Michal Hocko
SUSE Labs

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <df806a77-3327-9db5-8be2-976fde1c84e5@gmail.com>
     [not found] ` <20190117122535.njcbqhlmzozdkncw@mikami>
     [not found]   ` <1d36b181-cbaf-6694-1a31-2f7f55d15675@gmail.com>
     [not found]     ` <96ef6615-a5df-30af-b4dc-417a18ca63f1@gmail.com>
2019-01-25  7:52       ` pids.current with invalid value for hours [5.0.0 rc3 git] Arkadiusz Miśkiewicz
2019-01-25 16:37         ` Tejun Heo
2019-01-25 19:47           ` Arkadiusz Miśkiewicz
2019-01-26  1:27             ` Tetsuo Handa
2019-01-26  2:41               ` Arkadiusz Miśkiewicz
2019-01-26  6:10                 ` Tetsuo Handa
2019-01-26  7:55                   ` Tetsuo Handa
2019-01-26 11:09                     ` Tetsuo Handa
2019-01-26 11:29                       ` Arkadiusz Miśkiewicz
2019-01-26 13:10                         ` [PATCH v2] oom, oom_reaper: do not enqueue same task twice Tetsuo Handa
2019-01-27  8:37                           ` Michal Hocko
2019-01-27 10:56                             ` Tetsuo Handa
2019-01-27 11:40                               ` Michal Hocko [this message]
2019-01-27 14:57                                 ` [PATCH v3] " Tetsuo Handa
2019-01-27 16:58                                   ` Michal Hocko
2019-01-27 23:00                                   ` Roman Gushchin
2019-01-28 18:15                                   ` Andrew Morton
2019-01-28 18:42                                     ` Michal Hocko
2019-01-28 21:53                                   ` Johannes Weiner
2019-01-29 10:34                                     ` Tetsuo Handa
2019-01-26  1:41             ` pids.current with invalid value for hours [5.0.0 rc3 git] Roman Gushchin
2019-01-26  2:28               ` Arkadiusz Miśkiewicz

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