linux-kernel - Re: [PATCH 1/2] Revert "mm: don't reclaim inodes with many attached pages"

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Date:   Mon, 11 Feb 2019 16:34:34 +0100
From:   Wolfgang Walter <linux@...m.de>
To:     Jan Kara <jack@...e.cz>
Cc:     Dave Chinner <david@...morbit.com>, Roman Gushchin <guro@...com>,
        Michal Hocko <mhocko@...nel.org>, Chris Mason <clm@...com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        akpm@...ux-foundation.org, vdavydov.dev@...il.com
Subject: Re: [PATCH 1/2] Revert "mm: don't reclaim inodes with many attached pages"

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 small
> > caches that lower pressure but are equally important for
> > performance.
> > 
> > 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, but
> > on slower machines and storage, it will have a major impact.
> 
> Just as a data point, our performance testing infrastructure has bisected
> 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 (starting 
with 4.19.3) down to

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

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

We also see a performance regression compared to 4.14 even with this patch 
reverted, but much less dramatic.

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

172b06c32b949759fe6313abec514bc4f15014f4

and see if this helps.

Regards,
-- 
Wolfgang Walter
Studentenwerk München
Anstalt des öffentlichen Rechts