From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Michal Hocko <mhocko@kernel.org>,
David Rientjes <rientjes@google.com>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer.
Date: Wed, 27 Jun 2018 07:28:22 -0700 [thread overview]
Message-ID: <20180627142822.GV3593@linux.vnet.ibm.com> (raw)
In-Reply-To: <c0aeb719-ccb7-46c7-2ad9-b0630bf4d542@i-love.sakura.ne.jp>
On Wed, Jun 27, 2018 at 07:52:23PM +0900, Tetsuo Handa wrote:
> On 2018/06/27 8:50, Paul E. McKenney wrote:
> > On Wed, Jun 27, 2018 at 05:10:48AM +0900, Tetsuo Handa wrote:
> >> As far as I can see,
> >>
> >> - atomic_set(&oom_callback_count, 1);
> >> + atomic_inc(&oom_callback_count);
> >>
> >> should be sufficient.
> >
> > I don't see how that helps. For example, suppose that two tasks
> > invoked rcu_oom_notify() at about the same time. Then they could
> > both see oom_callback_count equal to zero, both atomically increment
> > oom_callback_count, then both do the IPI invoking rcu_oom_notify_cpu()
> > on each online CPU.
> >
> > So far, so good. But rcu_oom_notify_cpu() enqueues a per-CPU RCU
> > callback, and enqueuing the same callback twice in quick succession
> > would fatally tangle RCU's callback lists.
> >
> > What am I missing here?
>
> You are pointing out that "number of rsp->call() is called" > "number of
> rcu_oom_callback() is called" can happen if concurrently called, aren't you?
Yes. Reusing an rcu_head before invocation of the earlier use is
very bad indeed. ;-)
> Then, you are not missing anything. You will need to use something equivalent
> to oom_lock even if you can convert rcu_oom_notify() to use shrinkers.
What should I look at to work out whether it makes sense to convert
rcu_oom_notify() to shrinkers, and if so, how to go about it?
Or are you simply asking me to serialize rcu_oom_notify()? (Which is
of course not difficult, so please just let me know.)
Thanx, Paul
next prev parent reply other threads:[~2018-06-27 14:26 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-20 11:20 [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer Tetsuo Handa
2018-06-20 11:55 ` Michal Hocko
2018-06-20 12:21 ` Tetsuo Handa
2018-06-20 13:07 ` Michal Hocko
2018-06-25 13:03 ` peter enderborg
2018-06-25 13:07 ` Michal Hocko
2018-06-25 14:02 ` peter enderborg
2018-06-25 14:04 ` peter enderborg
2018-06-25 14:12 ` Michal Hocko
2018-06-20 22:36 ` David Rientjes
2018-06-21 7:31 ` Michal Hocko
2018-06-21 11:27 ` Tetsuo Handa
2018-06-21 12:05 ` Michal Hocko
2018-06-26 17:03 ` Paul E. McKenney
2018-06-26 20:10 ` Tetsuo Handa
2018-06-26 23:50 ` Paul E. McKenney
2018-06-27 10:52 ` Tetsuo Handa
2018-06-27 14:28 ` Paul E. McKenney [this message]
2018-06-27 7:22 ` Michal Hocko
2018-06-27 14:31 ` Paul E. McKenney
2018-06-28 11:39 ` Michal Hocko
2018-06-28 21:31 ` Paul E. McKenney
2018-06-29 9:04 ` Michal Hocko
2018-06-29 12:52 ` Paul E. McKenney
2018-06-29 13:26 ` Michal Hocko
2018-06-30 17:05 ` Paul E. McKenney
2018-07-02 12:00 ` Michal Hocko
2018-07-02 21:37 ` Paul E. McKenney
2018-07-03 7:24 ` Michal Hocko
2018-07-03 16:01 ` Paul E. McKenney
2018-07-06 5:39 ` Michal Hocko
2018-07-06 12:22 ` Paul E. McKenney
2018-06-29 14:35 ` Tetsuo Handa
2018-06-30 17:19 ` Paul E. McKenney
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