From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Michal Hocko <mhocko@kernel.org>
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: Thu, 28 Jun 2018 14:31:05 -0700 [thread overview]
Message-ID: <20180628213105.GP3593@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180628113942.GD32348@dhcp22.suse.cz>
On Thu, Jun 28, 2018 at 01:39:42PM +0200, Michal Hocko wrote:
> On Wed 27-06-18 07:31:25, Paul E. McKenney wrote:
> > On Wed, Jun 27, 2018 at 09:22:07AM +0200, Michal Hocko wrote:
> > > On Tue 26-06-18 10:03:45, Paul E. McKenney wrote:
> > > [...]
> > > > 3. Something else?
> > >
> > > How hard it would be to use a different API than oom notifiers? E.g. a
> > > shrinker which just kicks all the pending callbacks if the reclaim
> > > priority reaches low values (e.g. 0)?
> >
> > Beats me. What is a shrinker? ;-)
>
> This is a generich mechanism to reclaim memory that is not on standard
> LRU lists. Lwn.net surely has some nice coverage (e.g.
> https://lwn.net/Articles/548092/).
"In addition, there is little agreement over what a call to a shrinker
really means or how the called subsystem should respond." ;-)
Is this set up using register_shrinker() in mm/vmscan.c? I am guessing
that the many mentions of shrinker in DRM are irrelevant.
If my guess is correct, the API seems a poor fit for RCU. I can
produce an approximate number of RCU callbacks for ->count_objects(),
but a given callback might free a lot of memory or none at all. Plus,
to actually have ->scan_objects() free them before returning, I would
need to use something like rcu_barrier(), which might involve longer
delays than desired.
Or am I missing something here?
> > More seriously, could you please point me at an exemplary shrinker
> > use case so I can see what is involved?
>
> 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.
Thanx, Paul
next prev parent reply other threads:[~2018-06-28 21:29 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 [this message]
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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