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Date: Thu, 8 Aug 2019 15:51:25 +1000
From: Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH] [Regression, v5.0] mm: boosted kswapd reclaim b0rks
 system cache balance
Message-ID: <20190808055125.GV7777@dread.disaster.area>
References: <20190807091858.2857-1-david@fromorbit.com>
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To: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org, linux-xfs@vger.kernel.org, Vlastimil Babka <vbabka@suse.cz>

On Thu, Aug 08, 2019 at 10:30:25AM +1000, Dave Chinner wrote:
> On Thu, Aug 08, 2019 at 12:55:34AM +0100, Mel Gorman wrote:
> > On Thu, Aug 08, 2019 at 08:08:17AM +1000, Dave Chinner wrote:
> > > On Wed, Aug 07, 2019 at 04:03:16PM +0100, Mel Gorman wrote:
> > > > On Wed, Aug 07, 2019 at 11:30:56AM +0200, Michal Hocko wrote:
> > > > The boosting was not intended to target THP specifically -- it was meant
> > > > to help recover early from any fragmentation-related event for any user
> > > > that might need it. Hence, it's not tied to THP but even with THP
> > > > disabled, the boosting will still take effect.
> > > > 
> > > > One band-aid would be to disable watermark boosting entirely when THP is
> > > > disabled but that feels wrong. However, I would be interested in hearing
> > > > if sysctl vm.watermark_boost_factor=0 has the same effect as your patch.
> > > 
> > > <runs test>
> > > 
> > > Ok, it still runs it out of page cache, but it doesn't drive page
> > > cache reclaim as hard once there's none left. The IO patterns are
> > > less peaky, context switch rates are increased from ~3k/s to 15k/s
> > > but remain pretty steady.
> > > 
> > > Test ran 5s faster and  file rate improved by ~2%. So it's better
> > > once the page cache is largerly fully reclaimed, but it doesn't
> > > prevent the page cache from being reclaimed instead of inodes....
> > > 
> > 
> > Ok. Ideally you would also confirm the patch itself works as you want.
> > It *should* but an actual confirmation would be nice.
> 
> Yup, I'll get to that later today.

Looks good, does what it says on the tin.

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com