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Commit 2ab44f43 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
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mm: vmscan: decide whether to compact the pgdat based on reclaim progress 



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: default avatarMel Gorman <mgorman@suse.de>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Tested-by: default avatarZlatko Calusic <zcalusic@bitsync.net>
Cc: dormando <dormando@rydia.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b8e83b94

mm/vmscan.c

+30 −29
Original line number Diff line number Diff line
@@ -2661,7 +2661,8 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining, 
 */

static bool kswapd_shrink_zone(struct zone *zone,

			       struct scan_control *sc,

			       unsigned long lru_pages)

			       unsigned long lru_pages,

			       unsigned long *nr_attempted)

{

	unsigned long nr_slab;

	struct reclaim_state *reclaim_state = current->reclaim_state;
@@ -2677,6 +2678,9 @@ static bool kswapd_shrink_zone(struct zone *zone, 
	nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);

	sc->nr_reclaimed += reclaim_state->reclaimed_slab;



	/* Account for the number of pages attempted to reclaim */

	*nr_attempted += sc->nr_to_reclaim;



	if (nr_slab == 0 && !zone_reclaimable(zone))

		zone->all_unreclaimable = 1;
@@ -2724,7 +2728,9 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, 


	do {

		unsigned long lru_pages = 0;

		unsigned long nr_attempted = 0;

		bool raise_priority = true;

		bool pgdat_needs_compaction = (order > 0);



		sc.nr_reclaimed = 0;
@@ -2774,7 +2780,21 @@ 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);



			/*

			 * If any zone is currently balanced then kswapd will

			 * not call compaction as it is expected that the

			 * necessary pages are already available.

			 */

			if (pgdat_needs_compaction &&

					zone_watermark_ok(zone, order,

						low_wmark_pages(zone),

						*classzone_idx, 0))

				pgdat_needs_compaction = false;

		}



		/*
@@ -2843,7 +2863,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, 
				 * already being scanned that high

				 * watermark would be met at 100% efficiency.

				 */

				if (kswapd_shrink_zone(zone, &sc, lru_pages))

				if (kswapd_shrink_zone(zone, &sc, lru_pages,

						       &nr_attempted))

					raise_priority = false;

			}
@@ -2895,6 +2916,13 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, 
		if (try_to_freeze() || kthread_should_stop())

			break;



		/*

		 * Compact if necessary and kswapd is reclaiming at least the

		 * high watermark number of pages as requsted

		 */

		if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)

			compact_pgdat(pgdat, order);



		/*

		 * Raise priority if scanning rate is too low or there was no

		 * progress in reclaiming pages
@@ -2904,33 +2932,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, 
	} 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()