mm/vmscan: never demote for memcg reclaim

Global reclaim aims to reduce the amount of memory used on a given node or
set of nodes.  Migrating pages to another node serves this purpose.

memcg reclaim is different.  Its goal is to reduce the total memory
consumption of the entire memcg, across all nodes.  Migration does not
assist memcg reclaim because it just moves page contents between nodes
rather than actually reducing memory consumption.

Link: https://lkml.kernel.org/r/20210715055145.195411-9-ying.huang@intel.com
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Suggested-by: Yang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 219e4f4280ec61d01c051494e6bfc99fbb1cd6cd..ce8a27ece0bed7038d26d37e1cdbe91903cdc47a 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -524,8 +524,13 @@ static long add_nr_deferred(long nr, struct shrinker *shrinker,
 
 static bool can_demote(int nid, struct scan_control *sc)
 {
-       if (sc && sc->no_demotion)
-               return false;
+       if (sc) {
+               if (sc->no_demotion)
+                       return false;
+               /* It is pointless to do demotion in memcg reclaim */
+               if (cgroup_reclaim(sc))
+                       return false;
+       }
        if (next_demotion_node(nid) == NUMA_NO_NODE)
                return false;