And helper of memcg_get_e_css() so that the consumer needn't to
call cgroup_get_e_css(cgroup, &memory_cgrp_subsys) directly, since
&memory_cgrp_subsys has to be used in case that MEMCG is enabled.

Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ming Lei <redacted>
---
 include/linux/memcontrol.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index bfe5c486f4ad..741852addbd7 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h

@@ -1101,6 +1101,11 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 						gfp_t gfp_mask,
 						unsigned long *total_scanned);
 
+static inline
+struct cgroup_subsys_state *memcg_get_e_css(struct cgroup_subsys_state *css)