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Commit 4ef461e8 authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
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memcg: remove mem_cgroup_reclaimable check from soft reclaim 



mem_cgroup_reclaimable() checks whether a cgroup has reclaimable pages on
*any* NUMA node.  However, the only place where it's called is
mem_cgroup_soft_reclaim(), which tries to reclaim memory from a *specific*
zone.  So the way it is used is incorrect - it will return true even if
the cgroup doesn't have pages on the zone we're scanning.

I think we can get rid of this check completely, because
mem_cgroup_shrink_node_zone(), which is called by
mem_cgroup_soft_reclaim() if mem_cgroup_reclaimable() returns true, is
equivalent to shrink_lruvec(), which exits almost immediately if the
lruvec passed to it is empty.  So there's no need to optimize anything
here.  Besides, we don't have such a check in the general scan path
(shrink_zone) either.

Signed-off-by: default avatarVladimir Davydov <vdavydov@parallels.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 97ad2be1

mm/memcontrol.c

+0 −43
Original line number Diff line number Diff line
@@ -1743,52 +1743,11 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg) 
	memcg->last_scanned_node = node;

	return node;

}



/*

 * Check all nodes whether it contains reclaimable pages or not.

 * For quick scan, we make use of scan_nodes. This will allow us to skip

 * unused nodes. But scan_nodes is lazily updated and may not cotain

 * enough new information. We need to do double check.

 */

static bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap)

{

	int nid;



	/*

	 * quick check...making use of scan_node.

	 * We can skip unused nodes.

	 */

	if (!nodes_empty(memcg->scan_nodes)) {

		for (nid = first_node(memcg->scan_nodes);

		     nid < MAX_NUMNODES;

		     nid = next_node(nid, memcg->scan_nodes)) {



			if (test_mem_cgroup_node_reclaimable(memcg, nid, noswap))

				return true;

		}

	}

	/*

	 * Check rest of nodes.

	 */

	for_each_node_state(nid, N_MEMORY) {

		if (node_isset(nid, memcg->scan_nodes))

			continue;

		if (test_mem_cgroup_node_reclaimable(memcg, nid, noswap))

			return true;

	}

	return false;

}



#else

int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)

{

	return 0;

}



static bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap)

{

	return test_mem_cgroup_node_reclaimable(memcg, 0, noswap);

}

#endif



static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
@@ -1832,8 +1791,6 @@ static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg, 
			}

			continue;

		}

		if (!mem_cgroup_reclaimable(victim, false))

			continue;

		total += mem_cgroup_shrink_node_zone(victim, gfp_mask, false,

						     zone, &nr_scanned);

		*total_scanned += nr_scanned;