From: Michal Hocko <mhocko@kernel.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Matthew Wilcox <willy@infradead.org>,
lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>
Subject: Re: [Lsf-pc] [LSF/MM TOPIC] Congestion
Date: Tue, 7 Jan 2020 12:53:33 +0100 [thread overview]
Message-ID: <20200107115333.GF32178@dhcp22.suse.cz> (raw)
In-Reply-To: <20200106232100.GL23195@dread.disaster.area>
On Tue 07-01-20 10:21:00, Dave Chinner wrote:
> On Mon, Jan 06, 2020 at 12:55:14PM +0100, Michal Hocko wrote:
> > On Tue 31-12-19 04:59:08, Matthew Wilcox wrote:
> > >
> > > I don't want to present this topic; I merely noticed the problem.
> > > I nominate Jens Axboe and Michael Hocko as session leaders. See the
> > > thread here:
> >
> > Thanks for bringing this up Matthew! The change in the behavior came as
> > a surprise to me. I can lead the session for the MM side.
> >
> > > https://lore.kernel.org/linux-mm/20190923111900.GH15392@bombadil.infradead.org/
> > >
> > > Summary: Congestion is broken and has been for years, and everybody's
> > > system is sleeping waiting for congestion that will never clear.
> > >
> > > A good outcome for this meeting would be:
> > >
> > > - MM defines what information they want from the block stack.
> >
> > The history of the congestion waiting is kinda hairy but I will try to
> > summarize expectations we used to have and we can discuss how much of
> > that has been real and what followed up as a cargo cult. Maybe we just
> > find out that we do not need functionality like that anymore. I believe
> > Mel would be a great contributor to the discussion.
>
> We most definitely do need some form of reclaim throttling based on
> IO congestion, because it is trivial to drive the system into swap
> storms and OOM killer invocation when there are large dirty slab
> caches that require IO to make reclaim progress and there's little
> in the way of page cache to reclaim.
Just to clarify. I do agree that we need some form of throttling. Sorry
if my wording was confusing. What I meant is that I am not sure whether
wait_iff_congested as it is implemented now is the right way. We
definitely have to slow/block the reclaim when there is a lot of dirty
(meta)data. How to do that is a good topic to discuss.
[skipping the rest of the email which has many good points]
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-01-07 11:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-31 12:59 [LSF/MM TOPIC] Congestion Matthew Wilcox
2020-01-04 9:09 ` Dave Chinner
2020-01-06 11:55 ` [Lsf-pc] " Michal Hocko
2020-01-06 23:21 ` Dave Chinner
2020-01-07 8:23 ` Chris Murphy
2020-01-07 11:53 ` Michal Hocko
2020-01-07 20:12 ` Chris Murphy
2020-01-07 11:53 ` Michal Hocko [this message]
2020-01-09 11:07 ` Jan Kara
2020-01-09 23:00 ` Dave Chinner
2020-02-05 16:05 ` Mel Gorman
2020-02-06 23:19 ` Dave Chinner
2020-02-07 0:08 ` Matthew Wilcox
2020-02-13 3:18 ` Andrew Morton
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