From: Michal Hocko <mhocko@kernel.org>
To: Greg Thelen <gthelen@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Shakeel Butt <shakeelb@google.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] memcg, oom: move out_of_memory back to the charge path
Date: Tue, 3 Jul 2018 09:16:58 +0200 [thread overview]
Message-ID: <20180703071658.GC16767@dhcp22.suse.cz> (raw)
In-Reply-To: <xr938t6skd9m.fsf@gthelen.svl.corp.google.com>
On Tue 03-07-18 00:08:05, Greg Thelen wrote:
> Michal Hocko <mhocko@kernel.org> wrote:
>
> > On Fri 29-06-18 11:59:04, Greg Thelen wrote:
> >> Michal Hocko <mhocko@kernel.org> wrote:
> >>
> >> > On Thu 28-06-18 16:19:07, Greg Thelen wrote:
> >> >> Michal Hocko <mhocko@kernel.org> wrote:
> >> > [...]
> >> >> > + if (mem_cgroup_out_of_memory(memcg, mask, order))
> >> >> > + return OOM_SUCCESS;
> >> >> > +
> >> >> > + WARN(1,"Memory cgroup charge failed because of no reclaimable memory! "
> >> >> > + "This looks like a misconfiguration or a kernel bug.");
> >> >>
> >> >> I'm not sure here if the warning should here or so strongly worded. It
> >> >> seems like the current task could be oom reaped with MMF_OOM_SKIP and
> >> >> thus mem_cgroup_out_of_memory() will return false. So there's nothing
> >> >> alarming in that case.
> >> >
> >> > If the task is reaped then its charges should be released as well and
> >> > that means that we should get below the limit. Sure there is some room
> >> > for races but this should be still unlikely. Maybe I am just
> >> > underestimating though.
> >> >
> >> > What would you suggest instead?
> >>
> >> I suggest checking MMF_OOM_SKIP or deleting the warning.
> >
> > So what do you do when you have MMF_OOM_SKIP task? Do not warn? Checking
> > for all the tasks would be quite expensive and remembering that from the
> > task selection not nice either. Why do you think it would help much?
>
> I assume we could just check current's MMF_OOM_SKIP - no need to check
> all tasks.
I still do not follow. If you are after a single task memcg then we
should be ok. try_charge has a runaway for oom victims
if (unlikely(tsk_is_oom_victim(current) ||
fatal_signal_pending(current) ||
current->flags & PF_EXITING))
goto force;
regardless of MMF_OOM_SKIP. So if there is a single process in the
memcg, we kill it and the oom reaper kicks in and sets MMF_OOM_SKIP then
we should bail out there. Or do I miss your intention?
> My only (minor) objection is that the warning text suggests
> misconfiguration or kernel bug, when there may be neither.
>
> > I feel strongly that we have to warn when bypassing the charge limit
> > during the corner case because it can lead to unexpected behavior and
> > users should be aware of this fact. I am open to the wording or some
> > optimizations. I would prefer the latter on top with a clear description
> > how it helped in a particular case though. I would rather not over
> > optimize now without any story to back it.
>
> I'm fine with the warning. I know enough to look at dmesg logs to take
> an educates that the race occurred. We can refine it later if/when the
> reports start rolling in. No change needed.
OK. Thanks!
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-07-03 7:17 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-28 15:11 [PATCH] memcg, oom: move out_of_memory back to the charge path Michal Hocko
2018-06-28 23:19 ` Greg Thelen
2018-06-29 7:21 ` Michal Hocko
2018-06-29 18:59 ` Greg Thelen
2018-07-02 10:03 ` Michal Hocko
2018-07-03 7:08 ` Greg Thelen
2018-07-03 7:16 ` Michal Hocko [this message]
2018-07-03 23:29 ` Greg Thelen
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