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From:   Wolfgang Walter <linux@stwm.de>
To:     Jan Kara <jack@suse.cz>
Cc:     Dave Chinner <david@fromorbit.com>, Roman Gushchin <guro@fb.com>,
        Michal Hocko <mhocko@kernel.org>, Chris Mason <clm@fb.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
        akpm@linux-foundation.org, vdavydov.dev@gmail.com
Subject: Re: [PATCH 1/2] Revert "mm: don't reclaim inodes with many attached pages"
Date:   Mon, 11 Feb 2019 16:34:34 +0100
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Am Donnerstag, 7. Februar 2019, 11:27:50 schrieb Jan Kara:
> On Fri 01-02-19 09:19:04, Dave Chinner wrote:
> > Maybe for memcgs, but that's exactly the oppose of what we want to
> > do for global caches (e.g. filesystem metadata caches). We need to
> > make sure that a single, heavily pressured cache doesn't evict smal=
l
> > caches that lower pressure but are equally important for
> > performance.
> >=20
> > e.g. I've noticed recently a significant increase in RMW cycles in
> > XFS inode cache writeback during various benchmarks. It hasn't
> > affected performance because the machine has IO and CPU to burn, bu=
t
> > on slower machines and storage, it will have a major impact.
>=20
> Just as a data point, our performance testing infrastructure has bise=
cted
> down to the commits discussed in this thread as the cause of about 40=
%
> regression in XFS file delete performance in bonnie++ benchmark.

We also bisected our big IO-performance problem of an imap-server (star=
ting=20
with 4.19.3) down to

=09mm: don't reclaim inodes with many attached pages
=09commit a76cf1a474d7dbcd9336b5f5afb0162baa142cf0 upstream.

On other servers the filesystems sometimes seems to hang for 10 seconds=
 and=20
more.

We also see a performance regression compared to 4.14 even with this pa=
tch=20
reverted, but much less dramatic.

Now I saw this thread and I'll try to revert

172b06c32b949759fe6313abec514bc4f15014f4

and see if this helps.

Regards,
--=20
Wolfgang Walter
Studentenwerk M=FCnchen
Anstalt des =F6ffentlichen Rechts