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SubjectRe: [PATCH 1/2] Revert "mm: don't reclaim inodes with many attached pages"
Date
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

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