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

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Message-ID: <20190208212531.GN14116@dastard>
Date:   Sat, 9 Feb 2019 08:25:31 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jan Kara <jack@...e.cz>, 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>,
        "vdavydov.dev@...il.com" <vdavydov.dev@...il.com>
Subject: Re: [PATCH 1/2] Revert "mm: don't reclaim inodes with many attached
 pages"

On Thu, Feb 07, 2019 at 09:37:27PM -0800, Andrew Morton wrote:
> On Thu, 7 Feb 2019 11:27:50 +0100 Jan Kara <jack@...e.cz> wrote:
> 
> > 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.
> > 
> 
> Has anyone done significant testing with Rik's maybe-fix?

Apart from pointing out all the bugs and incorrect algorithmic
assumptions it makes, no.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com