linux-kernel - Re: [PATCH 06/27] mm, vmscan: Begin reclaiming pages on a per-node basis

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Message-ID: <20160223185722.GF13816@cmpxchg.org>
Date:	Tue, 23 Feb 2016 10:57:22 -0800
From:	Johannes Weiner <hannes@...xchg.org>
To:	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...riel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/27] mm, vmscan: Begin reclaiming pages on a per-node
 basis

On Tue, Feb 23, 2016 at 03:04:29PM +0000, Mel Gorman wrote:
> @@ -2428,10 +2448,11 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
>  			reclaimed = sc->nr_reclaimed;
>  			scanned = sc->nr_scanned;
>  
> +			sc->reclaim_idx = reclaim_idx;
>  			shrink_zone_memcg(zone, memcg, sc, &lru_pages);
>  			zone_lru_pages += lru_pages;

The setting of sc->reclaim_idx is unexpected here. Why not set it in
the caller and eliminate the reclaim_idx parameter?

> @@ -2558,16 +2579,12 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  		sc->gfp_mask |= __GFP_HIGHMEM;
>  
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
> -					requested_highidx, sc->nodemask) {

It's unfortunate that we start with the lowest zone here. For Normal
allocations, the most common allocations, this will always have two
full shrink_node() rounds that skip over everything >DMA in the first,
then over everything >DMA32 in the second, even though all pages on
the node are valid reclaim candidates for that allocation.