From: Wei Yang <richard.weiyang@gmail.com>
Subject: mm/memcg: set pos explicitly for reclaim and !reclaim

During mem_cgroup_iter, there are two ways to get iteration position:
reclaim vs non-reclaim mode.

Let's do it explicitly for reclaim vs non-reclaim mode.

Link: https://lkml.kernel.org/r/20220330234719.18340-3-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/mm/memcontrol.c~mm-memcg-set-pos-explicitly-for-reclaim-and-reclaim
+++ a/mm/memcontrol.c
@@ -1014,9 +1014,6 @@ struct mem_cgroup *mem_cgroup_iter(struc
 	if (!root)
 		root = root_mem_cgroup;
 
-	if (prev && !reclaim)
-		pos = prev;
-
 	rcu_read_lock();
 
 	if (reclaim) {
@@ -1042,6 +1039,8 @@ struct mem_cgroup *mem_cgroup_iter(struc
 			 */
 			(void)cmpxchg(&iter->position, pos, NULL);
 		}
+	} else if (prev) {
+		pos = prev;
 	}
 
 	if (pos)
_