From: Michal Hocko <mhocko@kernel.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
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: Fri, 29 Jun 2018 15:26:38 +0200 [thread overview]
Message-ID: <20180629132638.GD5963@dhcp22.suse.cz> (raw)
In-Reply-To: <20180629125218.GX3593@linux.vnet.ibm.com>
On Fri 29-06-18 05:52:18, Paul E. McKenney wrote:
> On Fri, Jun 29, 2018 at 11:04:19AM +0200, Michal Hocko wrote:
> > On Thu 28-06-18 14:31:05, Paul E. McKenney wrote:
> > > On Thu, Jun 28, 2018 at 01:39:42PM +0200, Michal Hocko wrote:
[...]
> > > > Well, I am not really sure what is the objective of the oom notifier to
> > > > point you to the right direction. IIUC you just want to kick callbacks
> > > > to be handled sooner under a heavy memory pressure, right? How is that
> > > > achieved? Kick a worker?
> > >
> > > That is achieved by enqueuing a non-lazy callback on each CPU's callback
> > > list, but only for those CPUs having non-empty lists. This causes
> > > CPUs with lists containing only lazy callbacks to be more aggressive,
> > > in particular, it prevents such CPUs from hanging out idle for seconds
> > > at a time while they have callbacks on their lists.
> > >
> > > The enqueuing happens via an IPI to the CPU in question.
> >
> > I am afraid this is too low level for my to understand what is going on
> > here. What are lazy callbacks and why do they need any specific action
> > when we are getting close to OOM? I mean, I do understand that we might
> > have many callers of call_rcu and free memory lazily. But there is quite
> > a long way before we start the reclaim until we reach the OOM killer path.
> > So why don't those callbacks get called during that time period? How are
> > their triggered when we are not hitting the OOM path? They surely cannot
> > sit there for ever, right? Can we trigger them sooner? Maybe the
> > shrinker is not the best fit but we have a retry feedback loop in the page
> > allocator, maybe we can kick this processing from there.
>
> The effect of RCU's current OOM code is to speed up callback invocation
> by at most a few seconds (assuming no stalled CPUs, in which case
> it is not possible to speed up callback invocation).
>
> Given that, I should just remove RCU's OOM code entirely?
Yeah, it seems so. I do not see how this would really help much. If we
really need some way to kick callbacks then we should do so much earlier
in the reclaim process - e.g. when we start struggling to reclaim any
memory.
I am curious. Has the notifier been motivated by a real world use case
or it was "nice thing to do"?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-06-29 13:26 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
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 [this message]
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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