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Message-ID: <a2be0855-c923-7338-ee37-941a6770f221@suse.cz>
Date: Thu, 16 Jun 2016 12:08:58 +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>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/27] mm: vmscan: Do not reclaim from kswapd if there is
any eligible zone
On 06/09/2016 08:04 PM, Mel Gorman wrote:
> kswapd scans from highest to lowest for a zone that requires balancing.
> This was necessary when reclaim was per-zone to fairly age pages on
> lower zones. Now that we are reclaiming on a per-node basis, any eligible
> zone can be used and pages will still be aged fairly. This patch avoids
> reclaiming excessively unless buffer_heads are over the limit and it's
> necessary to reclaim from a higher zone than requested by the waker of
> kswapd to relieve low memory pressure.
Looks like the code was even wrong before... if classzone_idx wasn't
already set to the highmem zone in the first place, it wouldn't look at it.
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
After fixing the bug below,
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> mm/vmscan.c | 32 +++++++++++++++++++-------------
> 1 file changed, 19 insertions(+), 13 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index e4f3e068b7a0..6663fc75c3bc 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3102,24 +3102,30 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
>
> sc.nr_reclaimed = 0;
>
> - /* Scan from the highest requested zone to dma */
> + /*
> + * If the number of buffer_heads in the machine exceeds the
> + * maximum allowed level and this node has a highmem zone,
> + * force kswapd to reclaim from it to relieve lowmem pressure.
> + */
> + if (buffer_heads_over_limit) {
> + for (i = MAX_NR_ZONES - 1; i >= 0; i++) {
i--
> + zone = pgdat->node_zones + i;
> + if (!populated_zone(zone))
> + continue;
> +
> + if (is_highmem_idx(i))
> + classzone_idx = i;
> + break;
> + }
> + }
> +
> + /* Only reclaim if there are no eligible zones */
> for (i = classzone_idx; i >= 0; i--) {
> zone = pgdat->node_zones + i;
> if (!populated_zone(zone))
> continue;
>
> - /*
> - * If the number of buffer_heads in the machine
> - * exceeds the maximum allowed level and this node
> - * has a highmem zone, force kswapd to reclaim from
> - * it to relieve lowmem pressure.
> - */
> - if (buffer_heads_over_limit && is_highmem_idx(i)) {
> - classzone_idx = i;
> - break;
> - }
> -
> - if (!zone_balanced(zone, order, 0)) {
> + if (!zone_balanced(zone, sc.order, classzone_idx)) {
> classzone_idx = i;
> break;
> }
>
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