linux-kernel - Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaims at each priority

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Message-ID: <20130321125939.GK6094@dhcp22.suse.cz>
Date:	Thu, 21 Mar 2013 13:59:39 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd
 reclaims at each priority

On Thu 21-03-13 09:47:13, Mel Gorman wrote:
> On Wed, Mar 20, 2013 at 05:18:47PM +0100, Michal Hocko wrote:
> > On Sun 17-03-13 13:04:07, Mel Gorman wrote:
> > [...]
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index 88c5fed..4835a7a 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -2593,6 +2593,32 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
> > >  }
> > >  
> > >  /*
> > > + * kswapd shrinks the zone by the number of pages required to reach
> > > + * the high watermark.
> > > + */
> > > +static void kswapd_shrink_zone(struct zone *zone,
> > > +			       struct scan_control *sc,
> > > +			       unsigned long lru_pages)
> > > +{
> > > +	unsigned long nr_slab;
> > > +	struct reclaim_state *reclaim_state = current->reclaim_state;
> > > +	struct shrink_control shrink = {
> > > +		.gfp_mask = sc->gfp_mask,
> > > +	};
> > > +
> > > +	/* Reclaim above the high watermark. */
> > > +	sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
> > 
> > OK, so the cap is at high watermark which sounds OK to me, although I
> > would expect balance_gap being considered here. Is it not used
> > intentionally or you just wanted to have a reasonable upper bound?
> > 
> 
> It's intentional. The balance_gap is taken into account before the
> decision to shrink but not afterwards. As the watermark check after
> shrinking is based on just the high watermark, I decided to have
> shrink_zone reclaim on that basis.

OK, it makes sense. Thanks both you and Rik for clarification.

-- 
Michal Hocko
SUSE Labs
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