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Date: Mon, 18 Mar 2013 19:35:04 +0800
From: Hillf Danton <dhillf@...il.com>
To: Mel Gorman <mgorman@...e.de>
Cc: Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>,
Valdis Kletnieks <Valdis.Kletnieks@...edu>,
Rik van Riel <riel@...hat.com>,
Zlatko Calusic <zcalusic@...sync.net>,
Johannes Weiner <hannes@...xchg.org>,
dormando <dormando@...ia.net>,
Satoru Moriya <satoru.moriya@....com>, Mi@...per.es,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] mm: vmscan: Decide whether to compact the pgdat
based on reclaim progress
On Sun, Mar 17, 2013 at 9:04 PM, Mel Gorman <mgorman@...e.de> wrote:
> In the past, kswapd makes a decision on whether to compact memory after the
> pgdat was considered balanced. This more or less worked but it is late to
> make such a decision and does not fit well now that kswapd makes a decision
> whether to exit the zone scanning loop depending on reclaim progress.
>
> This patch will compact a pgdat if at least the requested number of pages
> were reclaimed from unbalanced zones for a given priority. If any zone is
> currently balanced, kswapd will not call compaction as it is expected the
> necessary pages are already available.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
> mm/vmscan.c | 52 +++++++++++++++++++++-------------------------------
> 1 file changed, 21 insertions(+), 31 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 279d0c2..7513bd1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2694,8 +2694,11 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>
> do {
> unsigned long lru_pages = 0;
> + unsigned long nr_to_reclaim = 0;
> unsigned long nr_reclaimed = sc.nr_reclaimed;
> + unsigned long this_reclaimed;
> bool raise_priority = true;
> + bool pgdat_needs_compaction = true;
To show that compaction is needed iff non order-o reclaim,
bool do_compaction = !!order;
>
> /*
> * Scan in the highmem->dma direction for the highest
> @@ -2743,7 +2746,17 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> for (i = 0; i <= end_zone; i++) {
> struct zone *zone = pgdat->node_zones + i;
>
> + if (!populated_zone(zone))
> + continue;
> +
> lru_pages += zone_reclaimable_pages(zone);
> +
> + /* Check if the memory needs to be defragmented */
Enrich the comment with, say,
/*If any zone is
currently balanced, kswapd will not call compaction as it is expected the
necessary pages are already available.*/
please since a big one is deleted below.
> + if (order && pgdat_needs_compaction &&
> + zone_watermark_ok(zone, order,
> + low_wmark_pages(zone),
> + *classzone_idx, 0))
> + pgdat_needs_compaction = false;
> }
>
> /*
> @@ -2814,6 +2827,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> */
> if (kswapd_shrink_zone(zone, &sc, lru_pages))
> raise_priority = false;
> +
> + nr_to_reclaim += sc.nr_to_reclaim;
> }
>
> /*
> @@ -2864,46 +2879,21 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> if (try_to_freeze() || kthread_should_stop())
> break;
>
> - /* If no reclaim progress then increase scanning priority */
> - if (sc.nr_reclaimed - nr_reclaimed == 0)
> - raise_priority = true;
> + /* Compact if necessary and kswapd is reclaiming efficiently */
> + this_reclaimed = sc.nr_reclaimed - nr_reclaimed;
> + if (order && pgdat_needs_compaction &&
> + this_reclaimed > nr_to_reclaim)
> + compact_pgdat(pgdat, order);
>
> /*
> * Raise priority if scanning rate is too low or there was no
> * progress in reclaiming pages
> */
> - if (raise_priority || sc.nr_reclaimed - nr_reclaimed == 0)
> + if (raise_priority || !this_reclaimed)
> sc.priority--;
> } while (sc.priority >= 0 &&
> !pgdat_balanced(pgdat, order, *classzone_idx));
>
> - /*
> - * If kswapd was reclaiming at a higher order, it has the option of
> - * sleeping without all zones being balanced. Before it does, it must
> - * ensure that the watermarks for order-0 on *all* zones are met and
> - * that the congestion flags are cleared. The congestion flag must
> - * be cleared as kswapd is the only mechanism that clears the flag
> - * and it is potentially going to sleep here.
> - */
> - if (order) {
> - int zones_need_compaction = 1;
> -
> - for (i = 0; i <= end_zone; i++) {
> - struct zone *zone = pgdat->node_zones + i;
> -
> - if (!populated_zone(zone))
> - continue;
> -
> - /* Check if the memory needs to be defragmented. */
> - if (zone_watermark_ok(zone, order,
> - low_wmark_pages(zone), *classzone_idx, 0))
> - zones_need_compaction = 0;
> - }
> -
> - if (zones_need_compaction)
> - compact_pgdat(pgdat, order);
> - }
> -
> out:
> /*
> * Return the order we were reclaiming at so prepare_kswapd_sleep()
> --
> 1.8.1.4
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