linux-kernel - Re: [PATCH 09/31] mm, vmscan: by default have direct reclaim only shrink once per node

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Date:	Thu, 7 Jul 2016 11:27:26 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...riel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/31] mm, vmscan: by default have direct reclaim only
 shrink once per node

On Thu, Jul 07, 2016 at 10:43:22AM +0900, Joonsoo Kim wrote:
> > @@ -2600,6 +2593,16 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> >  			classzone_idx--;
> >  
> >  		/*
> > +		 * Shrink each node in the zonelist once. If the zonelist is
> > +		 * ordered by zone (not the default) then a node may be
> > +		 * shrunk multiple times but in that case the user prefers
> > +		 * lower zones being preserved
> > +		 */
> > +		if (zone->zone_pgdat == last_pgdat)
> > +			continue;
> > +		last_pgdat = zone->zone_pgdat;
> > +
> > +		/*
> 
> After this change, compaction_ready() which uses zone information
> would be called with highest zone in node. So, if some lower zone in
> that node is compaction-ready, we cannot stop the reclaim.
> 

Yes. It only impacts direct reclaim but potentially it's an issue. I'll
fix it.

-- 
Mel Gorman
SUSE Labs