[PATCH v2] mm/memcg: bail out early when !memcg in mem_cgroup_lruvec

[Alex Shi]

Sometime, we use NULL memcg in mem_cgroup_lruvec(memcg, pgdat)
so we could get out early in the situation to avoid useless checking.

Polished as Andrew Morton's suggestion.

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Cc: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 include/linux/memcontrol.h | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 3e6a1df3bdb9..4ff2ffe2b73d 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -610,20 +610,17 @@ mem_cgroup_nodeinfo(struct mem_cgroup *memcg, int nid)
 static inline struct lruvec *mem_cgroup_lruvec(struct mem_cgroup *memcg,
 					       struct pglist_data *pgdat)
 {
-	struct mem_cgroup_per_node *mz;
 	struct lruvec *lruvec;
 
-	if (mem_cgroup_disabled()) {
+	if (mem_cgroup_disabled() || !memcg) {
 		lruvec = &pgdat->__lruvec;
-		goto out;
-	}
+	} else {
+		struct mem_cgroup_per_node *mz;
 
-	if (!memcg)
-		memcg = root_mem_cgroup;
+		mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
+		lruvec = &mz->lruvec;
+	}
 
-	mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
-	lruvec = &mz->lruvec;
-out:
 	/*
 	 * Since a node can be onlined after the mem_cgroup was created,
 	 * we have to be prepared to initialize lruvec->pgdat here;
-- 
2.29.GIT