Commit a2d7f8e4 authored May 03, 2017 by Johannes Weiner Committed by Linus Torvalds May 03, 2017

mm: don't avoid high-priority reclaim on unreclaimable nodes

Commit 246e87a9 ("memcg: fix get_scan_count() for small targets")
sought to avoid high reclaim priorities for kswapd by forcing it to scan
a minimum amount of pages when lru_pages >> priority yielded nothing.

Commit b95a2f2d ("mm: vmscan: convert global reclaim to per-memcg
LRU lists"), due to switching global reclaim to a round-robin scheme
over all cgroups, had to restrict this forceful behavior to
unreclaimable zones in order to prevent massive overreclaim with many
cgroups.

The latter patch effectively neutered the behavior completely for all
but extreme memory pressure.  But in those situations we might as well
drop the reclaimers to lower priority levels.  Remove the check.

Link: http://lkml.kernel.org/r/20170228214007.5621-6-hannes@cmpxchg.org


Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Jia He <hejianet@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 15038d0d

mm/vmscan.c

+5 −14

Original line number	Diff line number	Diff line
		@@ -2130,22 +2130,13 @@ static void get_scan_count(struct lruvec lruvec, struct mem_cgroup memcg,
		int pass;

		/*
		* If the zone or memcg is small, nr[l] can be 0. This
		* results in no scanning on this priority and a potential
		* priority drop. Global direct reclaim can go to the next
		* zone and tends to have no problems. Global kswapd is for
		* zone balancing and it needs to scan a minimum amount. When
		* If the zone or memcg is small, nr[l] can be 0. When
		* reclaiming for a memcg, a priority drop can cause high
		* latencies, so it's better to scan a minimum amount there as
		* well.
		* latencies, so it's better to scan a minimum amount. When a
		* cgroup has already been deleted, scrape out the remaining
		* cache forcefully to get rid of the lingering state.
		*/
		if (current_is_kswapd()) {
		if (!pgdat_reclaimable(pgdat))
		force_scan = true;
		if (!mem_cgroup_online(memcg))
		force_scan = true;
		}
		if (!global_reclaim(sc))
		if (!global_reclaim(sc) \|\| !mem_cgroup_online(memcg))
		force_scan = true;

		/* If we have no swap space, do not bother scanning anon pages. */

Admin message