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: Tue, 26 Jun 2018 16:50:14 -0700 [thread overview]
Message-ID: <20180626235014.GS3593@linux.vnet.ibm.com> (raw)
In-Reply-To: <f40d85e0-1d90-2261-99a4-4db315df4860@i-love.sakura.ne.jp>
On Wed, Jun 27, 2018 at 05:10:48AM +0900, Tetsuo Handa wrote:
> On 2018/06/27 2:03, Paul E. McKenney wrote:
> > There are a lot of ways it could be made concurrency safe. If you need
> > me to do this, please do let me know.
> >
> > That said, the way it is now written, if you invoke rcu_oom_notify()
> > twice in a row, the second invocation will wait until the memory from
> > the first invocation is freed. What do you want me to do if you invoke
> > me concurrently?
> >
> > 1. One invocation "wins", waits for the earlier callbacks to
> > complete, then encourages any subsequent callbacks to be
> > processed more quickly. The other invocations return
> > immediately without doing anything.
> >
> > 2. The invocations serialize, with each invocation waiting for
> > the callbacks from previous invocation (in mutex_lock() order
> > or some such), and then starting a new round.
> >
> > 3. Something else?
> >
> > Thanx, Paul
>
> 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?
Thanx, Paul
next prev parent reply other threads:[~2018-06-26 23:48 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 [this message]
2018-06-27 10:52 ` Tetsuo Handa
2018-06-27 14:28 ` Paul E. McKenney
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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