Commit 86c79f6b authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

mm: vmscan: do not reclaim from kswapd if there is any eligible zone 

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.

[hillf.zj@alibaba-inc.com: Force kswapd reclaim no more than needed]
Link: http://lkml.kernel.org/r/1466518566-30034-12-git-send-email-mgorman@techsingularity.net
Link: http://lkml.kernel.org/r/1467970510-21195-13-git-send-email-mgorman@techsingularity.net


Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarHillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6256c6b4

mm/vmscan.c

+27 −32
Original line number Diff line number Diff line
@@ -3144,31 +3144,39 @@ 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 */

		for (i = classzone_idx; i >= 0; i--) {

		/*

		 * If the number of buffer_heads in the machine exceeds the

		 * maximum allowed level then reclaim from all zones. This is

		 * not specific to highmem as highmem may not exist but it is

		 * it is expected that buffer_heads are stripped in writeback.

		 */

		if (buffer_heads_over_limit) {

			for (i = MAX_NR_ZONES - 1; 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)) {

				classzone_idx = i;

				break;

			}

		}



		if (i < 0)

		/*

		 * Only reclaim if there are no eligible zones. Check from

		 * high to low zone as allocations prefer higher zones.

		 * Scanning from low to high zone would allow congestion to be

		 * cleared during a very small window when a small low

		 * zone was balanced even under extreme pressure when the

		 * overall node may be congested.

		 */

		for (i = classzone_idx; i >= 0; i--) {

			zone = pgdat->node_zones + i;

			if (!populated_zone(zone))

				continue;



			if (zone_balanced(zone, sc.order, classzone_idx))

				goto out;

		}



		/*

		 * Do some background aging of the anon list, to give
@@ -3213,19 +3221,6 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) 
		if (try_to_freeze() || kthread_should_stop())

			break;



		/*

		 * Stop reclaiming if any eligible zone is balanced and clear

		 * node writeback or congested.

		 */

		for (i = 0; i <= classzone_idx; i++) {

			zone = pgdat->node_zones + i;

			if (!populated_zone(zone))

				continue;



			if (zone_balanced(zone, sc.order, classzone_idx))

				goto out;

		}



		/*

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

		 * progress in reclaiming pages

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