Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 31 Jan 2019 12:34:03 +1100
From:   Dave Chinner <david@fromorbit.com>
To:     Chris Mason <clm@fb.com>
Cc:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
        Roman Gushchin <guro@fb.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "mhocko@kernel.org" <mhocko@kernel.org>,
        "vdavydov.dev@gmail.com" <vdavydov.dev@gmail.com>
Subject: Re: [PATCH 1/2] Revert "mm: don't reclaim inodes with many attached
 pages"
Message-ID: <20190131013403.GI4205@dastard>
References: <20190130041707.27750-1-david@fromorbit.com>
 <20190130041707.27750-2-david@fromorbit.com>
 <25EAF93D-BC63-4409-AF21-F45B2DDF5D66@fb.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <25EAF93D-BC63-4409-AF21-F45B2DDF5D66@fb.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@redhat.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@fromorbit.com