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

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Message-ID: <20190131013403.GI4205@dastard>
Date:   Thu, 31 Jan 2019 12:34:03 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Chris Mason <clm@...com>
Cc:     "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>,
        Roman Gushchin <guro@...com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mhocko@...nel.org" <mhocko@...nel.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 Wed, Jan 30, 2019 at 12:21:07PM +0000, Chris Mason wrote:
> 
> 
> On 29 Jan 2019, at 23:17, Dave Chinner wrote:
> 
> > From: Dave Chinner <dchinner@...hat.com>
> >
> > This reverts commit a76cf1a474d7dbcd9336b5f5afb0162baa142cf0.
> >
> > This change causes serious changes to page cache and inode cache
> > behaviour and balance, resulting in major performance regressions
> > when combining worklaods such as large file copies and kernel
> > compiles.
> >
> > https://bugzilla.kernel.org/show_bug.cgi?id=202441
> 
> I'm a little confused by the latest comment in the bz:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=202441#c24

Which says the first patch that changed the shrinker behaviour is
the underlying cause of the regression.

> Are these reverts sufficient?

I think so.

> Roman beat me to suggesting Rik's followup.  We hit a different problem 
> in prod with small slabs, and have a lot of instrumentation on Rik's 
> code helping.

I think that's just another nasty, expedient hack that doesn't solve
the underlying problem. Solving the underlying problem does not
require changing core reclaim algorithms and upsetting a page
reclaim/shrinker balance that has been stable and worked well for
just about everyone for years.

Cheers,

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