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Date:   Sat, 2 Feb 2019 10:39:05 +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: <20190201233905.GW6173@dastard>
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On Thu, Jan 31, 2019 at 03:48:11PM +0000, Chris Mason wrote:
> On 30 Jan 2019, at 20:34, Dave Chinner wrote:
> 
> > 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.
> 
> Based on the latest comment:
> 
> "If I had been less strict in my testing I probably would have 
> discovered that the problem was present earlier than 4.19.3. Mr Gushins 
> commit made it more visible.
> I'm going back to work after two days off, so I might not be able to 
> respond inside your working hours, but I'll keep checking in on this as 
> I get a chance."
> 
> I don't think the reverts are sufficient.

Roger has tested the two reverts more heavily against 5.0.0-rc3.
Without the reverts, the machine locks up hard. With the two reverts
applied, it runs along smoothly under extremely heavy load.

https://bugzilla.kernel.org/show_bug.cgi?id=202441#c26

So, yes, these changes need to be reverted.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com