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Commit ac34a1a3 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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memcg: fix direct softlimit reclaim to be called in limit path 



Commit d149e3b2 ("memcg: add the soft_limit reclaim in global direct
reclaim") adds a softlimit hook to shrink_zones().  By this, soft limit
is called as

   try_to_free_pages()
       do_try_to_free_pages()
           shrink_zones()
               mem_cgroup_soft_limit_reclaim()

Then, direct reclaim is memcg softlimit hint aware, now.

But, the memory cgroup's "limit" path can call softlimit shrinker.

   try_to_free_mem_cgroup_pages()
       do_try_to_free_pages()
           shrink_zones()
               mem_cgroup_soft_limit_reclaim()

This will cause a global reclaim when a memcg hits limit.

This is bug. soft_limit_reclaim() should be called when
scanning_global_lru(sc) == true.

And the commit adds a variable "total_scanned" for counting softlimit
scanned pages....it's not "total".  This patch removes the variable and
update sc->nr_scanned instead of it.  This will affect shrink_slab()'s
scan condition but, global LRU is scanned by softlimit and I think this
change makes sense.

TODO: avoid too much scanning of a zone when softlimit did enough work.

Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Ying Han <yinghan@google.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 26c4caea

mm/vmscan.c

+15 −12
Original line number Diff line number Diff line
@@ -1995,14 +1995,13 @@ static void shrink_zone(int priority, struct zone *zone, 
 * If a zone is deemed to be full of pinned pages then just give it a light

 * scan then give up on it.

 */

static unsigned long shrink_zones(int priority, struct zonelist *zonelist,

static void shrink_zones(int priority, struct zonelist *zonelist,

					struct scan_control *sc)

{

	struct zoneref *z;

	struct zone *zone;

	unsigned long nr_soft_reclaimed;

	unsigned long nr_soft_scanned;

	unsigned long total_scanned = 0;



	for_each_zone_zonelist_nodemask(zone, z, zonelist,

					gfp_zone(sc->gfp_mask), sc->nodemask) {
@@ -2017,19 +2016,23 @@ static unsigned long shrink_zones(int priority, struct zonelist *zonelist, 
				continue;

			if (zone->all_unreclaimable && priority != DEF_PRIORITY)

				continue;	/* Let kswapd poll it */

		}



			/*

			 * This steals pages from memory cgroups over softlimit

			 * and returns the number of reclaimed pages and

			 * scanned pages. This works for global memory pressure

			 * and balancing, not for a memcg's limit.

			 */

			nr_soft_scanned = 0;

			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,

						sc->order, sc->gfp_mask,

						&nr_soft_scanned);

			sc->nr_reclaimed += nr_soft_reclaimed;

		total_scanned += nr_soft_scanned;

			sc->nr_scanned += nr_soft_scanned;

			/* need some check for avoid more shrink_zone() */

		}



		shrink_zone(priority, zone, sc);

	}



	return total_scanned;

}



static bool zone_reclaimable(struct zone *zone)
@@ -2094,7 +2097,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 
		sc->nr_scanned = 0;

		if (!priority)

			disable_swap_token(sc->mem_cgroup);

		total_scanned += shrink_zones(priority, zonelist, sc);

		shrink_zones(priority, zonelist, sc);

		/*

		 * Don't shrink slabs when reclaiming memory from

		 * over limit cgroups