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Date: Thu, 23 Jun 2016 12:07:28 +0100
From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>, Linux-MM <linux-mm@kvack.org>,
        Rik van Riel <riel@surriel.com>, Johannes Weiner <hannes@cmpxchg.org>,
        LKML <linux-kernel@vger.kernel.org>, Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 04/27] mm, vmscan: Begin reclaiming pages on a per-node
 basis
Message-ID: <20160623110728.GT1868@techsingularity.net>
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On Wed, Jun 22, 2016 at 06:00:12PM +0200, Vlastimil Babka wrote:
> >>-		enum zone_type classzone_idx;
> >>-
> >> 		if (!populated_zone(zone))
> >> 			continue;
> >>
> >>-		classzone_idx = requested_highidx;
> >>+		/*
> >>+		 * Note that reclaim_idx does not change as it is the highest
> >>+		 * zone reclaimed from which for empty zones is a no-op but
> >>+		 * classzone_idx is used by shrink_node to test if the slabs
> >>+		 * should be shrunk on a given node.
> >>+		 */
> >> 		while (!populated_zone(zone->zone_pgdat->node_zones +
> >>-							classzone_idx))
> >>+							classzone_idx)) {
> >> 			classzone_idx--;
> >>+			continue;
> 
> Oh and Michal's comment on Patch 20 made me realize that my objection to v6
> about possible underflow of sc->reclaim_idx and classzone_idx seems to still
> apply here for classzone_idx?

Potentially. The relevant code now looks like this

                classzone_idx = sc->reclaim_idx;
                while (!populated_zone(zone->zone_pgdat->node_zones +
                                                        classzone_idx))
                        classzone_idx--;

-- 
Mel Gorman
SUSE Labs