From: Dave Hansen <dave.hansen@linux.intel.com>
Date: Thu, 2 Sep 2021 14:59:30 -0700
Subject: mm/vmscan: never demote for memcg reclaim
Git-commit: 3a235693d3930e1276c8d9cc0ca5807ef292cf0a
Patch-mainline: v5.15-rc1
References: jsc#PED-1247

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: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/vmscan.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -524,8 +524,13 @@ static long add_nr_deferred(long nr, str
 
 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;