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From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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 07:45:06 +0100	[thread overview]
Message-ID: <20160206064505.GB20537@dhcp22.suse.cz> (raw)
In-Reply-To: <20160204144319.GD14425@dhcp22.suse.cz>

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.

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:

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

  parent reply	other threads:[~2016-02-06  6:45 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 [this message]
2016-02-06 14:33         ` Tetsuo Handa
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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