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

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Date:   Thu, 7 Feb 2019 11:27:50 +0100
From:   Jan Kara <jack@...e.cz>
To:     Dave Chinner <david@...morbit.com>
Cc:     Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        Chris Mason <clm@...com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "vdavydov.dev@...il.com" <vdavydov.dev@...il.com>
Subject: Re: [PATCH 1/2] Revert "mm: don't reclaim inodes with many attached
 pages"

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.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR