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:

quoted

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
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