Re: [PATCH] [Regression, v5.0] mm: boosted kswapd reclaim b0rks system cache balance

Dave Chinner
2019-08-08T05:52:36Z

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