linux-kernel - Re: [PATCH 25/34] mm, vmscan: avoid passing in classzone_idx unnecessarily to compaction

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Message-ID: <ac068319-a38d-4514-c075-a09b88d2d979@suse.cz>
Date:	Thu, 14 Jul 2016 14:12:28 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Mel Gorman <mgorman@...hsingularity.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>
Cc:	Rik van Riel <riel@...riel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 25/34] mm, vmscan: avoid passing in classzone_idx
 unnecessarily to compaction_ready

On 07/08/2016 11:35 AM, Mel Gorman wrote:
> The scan_control structure has enough information available for
> compaction_ready() to make a decision. The classzone_idx manipulations in
> shrink_zones() are no longer necessary as the highest populated zone is
> no longer used to determine if shrink_slab should be called or not.
>
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> @@ -2621,8 +2609,8 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  			 */
>  			if (IS_ENABLED(CONFIG_COMPACTION) &&
>  			    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
> -			    zonelist_zone_idx(z) <= classzone_idx &&
> -			    compaction_ready(zone, sc->order, classzone_idx)) {
> +			    zonelist_zone_idx(z) <= sc->reclaim_idx &&

Hm I notice that the condition on the line above should be always true 
as the same sc->reclaim_idx value is used to limit zone_idx in 
for_each_zone_zonelist_nodemask(). The implication was probably true 
even before this patch (classzone_idx would be <= sc->reclaim_idx), but 
now it stands out clearly.

> +			    compaction_ready(zone, sc)) {
>  				sc->compaction_ready = true;
>  				continue;
>  			}
>