From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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
Subject: Re: [PATCH 3/5] oom: clear TIF_MEMDIE after oom_reaper managed to unmap the address space
Date: Sat, 6 Feb 2016 23:33:24 +0900 [thread overview]
Message-ID: <201602062333.CCI64980.MFJFFVOLtOOQSH@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20160206064505.GB20537@dhcp22.suse.cz>
Michal Hocko wrote:
> On Thu 04-02-16 15:43:19, Michal Hocko wrote:
> > On Thu 04-02-16 23:22:18, Tetsuo Handa wrote:
> > > Michal Hocko wrote:
> > > > From: Michal Hocko <mhocko@suse.com>
> > > >
> > > > When oom_reaper manages to unmap all the eligible vmas there shouldn't
> > > > be much of the freable memory held by the oom victim left anymore so it
> > > > makes sense to clear the TIF_MEMDIE flag for the victim and allow the
> > > > OOM killer to select another task.
> > >
> > > Just a confirmation. Is it safe to clear TIF_MEMDIE without reaching do_exit()
> > > with regard to freezing_slow_path()? Since clearing TIF_MEMDIE from the OOM
> > > reaper confuses
> > >
> > > wait_event(oom_victims_wait, !atomic_read(&oom_victims));
> > >
> > > in oom_killer_disable(), I'm worrying that the freezing operation continues
> > > before the OOM victim which escaped the __refrigerator() actually releases
> > > memory. Does this cause consistency problem?
> >
> > This is a good question! At first sight it seems this is not safe and we
> > might need to make the oom_reaper freezable so that it doesn't wake up
> > during suspend and interfere. Let me think about that.
>
> OK, I was thinking about it some more and it seems you are right here.
> oom_reaper as a kernel thread is not freezable automatically and so it
> might interfere after all the processes/kernel threads are considered
> frozen. Then it really might shut down TIF_MEMDIE too early and wake out
> oom_killer_disable. wait_event_freezable is not sufficient because the
> oom_reaper might running while the PM freezer is freezing tasks and it
> will miss it because it doesn't see it.
I'm not using PM freezer, but your answer is opposite to my guess.
I thought try_to_freeze_tasks(false) is called by freeze_kernel_threads()
after oom_killer_disable() succeeded, and try_to_freeze_tasks(false) will
freeze both userspace tasks (including OOM victims which got TIF_MEMDIE
cleared by the OOM reaper) and kernel threads (including the OOM reaper).
Thus, I was guessing that clearing TIF_MEMDIE without reaching do_exit() is
safe.
>
> So I think we might need this. I am heading to vacation today and will
> be offline for the next week so I will prepare the full patch with the
> proper changelog after I get back:
>
I can't judge whether we need this set_freezable().
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index ca61e6cfae52..7e9953a64489 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -521,6 +521,8 @@ static void oom_reap_task(struct task_struct *tsk)
>
> static int oom_reaper(void *unused)
> {
> + set_freezable();
> +
> while (true) {
> struct task_struct *tsk = NULL;
>
> --
> Michal Hocko
> SUSE Labs
>
next prev parent reply other threads:[~2016-02-06 14:33 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-03 13:13 [PATCH 0/5] oom reaper v5 Michal Hocko
2016-02-03 13:13 ` [PATCH 1/5] mm, oom: introduce oom reaper Michal Hocko
2016-02-03 23:48 ` David Rientjes
2016-02-04 6:41 ` Michal Hocko
2016-02-06 13:22 ` Tetsuo Handa
2016-02-15 20:50 ` Michal Hocko
2016-02-03 13:13 ` [PATCH 2/5] oom reaper: handle mlocked pages Michal Hocko
2016-02-03 23:57 ` David Rientjes
2016-02-23 1:36 ` David Rientjes
2016-02-23 13:21 ` Michal Hocko
2016-02-29 3:19 ` Hugh Dickins
2016-02-29 13:41 ` Michal Hocko
2016-03-08 13:40 ` Michal Hocko
2016-03-08 20:07 ` Hugh Dickins
2016-03-09 8:26 ` Michal Hocko
2016-02-03 13:13 ` [PATCH 3/5] oom: clear TIF_MEMDIE after oom_reaper managed to unmap the address space Michal Hocko
2016-02-04 14:22 ` Tetsuo Handa
2016-02-04 14:43 ` Michal Hocko
2016-02-04 15:08 ` Tetsuo Handa
2016-02-04 16:31 ` Michal Hocko
2016-02-05 11:14 ` Tetsuo Handa
2016-02-06 8:30 ` Michal Hocko
2016-02-06 11:23 ` Tetsuo Handa
2016-02-15 20:47 ` Michal Hocko
2016-02-06 6:45 ` Michal Hocko
2016-02-06 14:33 ` Tetsuo Handa [this message]
2016-02-15 20:40 ` [PATCH 3.1/5] oom: make oom_reaper freezable Michal Hocko
2016-02-03 13:13 ` [PATCH 4/5] mm, oom_reaper: report success/failure Michal Hocko
2016-02-03 23:10 ` David Rientjes
2016-02-04 6:46 ` Michal Hocko
2016-02-04 22:31 ` David Rientjes
2016-02-05 9:26 ` Michal Hocko
2016-02-06 6:34 ` Michal Hocko
2016-02-03 13:14 ` [PATCH 5/5] mm, oom_reaper: implement OOM victims queuing Michal Hocko
2016-02-04 10:49 ` Tetsuo Handa
2016-02-04 14:53 ` Michal Hocko
2016-02-06 5:54 ` Tetsuo Handa
2016-02-06 8:37 ` Michal Hocko
2016-02-06 15:33 ` Tetsuo Handa
2016-02-15 20:15 ` Michal Hocko
2016-02-16 11:11 ` Tetsuo Handa
2016-02-16 15:53 ` Michal Hocko
2016-02-17 9:48 ` [PATCH 6/5] oom, oom_reaper: disable oom_reaper for Michal Hocko
2016-02-17 10:41 ` Tetsuo Handa
2016-02-17 11:33 ` Michal Hocko
2016-02-19 18:34 ` Michal Hocko
2016-02-20 2:32 ` [PATCH 6/5] oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task Tetsuo Handa
2016-02-22 9:41 ` Michal Hocko
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