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: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3734fd6..32e3b19 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -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;