[PATCH 2/4] mm/memcontrol.c: use accessor to get id from css

[Jianyu Zhan]

This is a prepared patch for converting from per-cgroup id to
per-subsystem id.

We should not access per-cgroup id directly, since this is implemetation
detail. Use the accessor css_from_id() instead.

This patch has no functional change.

Signed-off-by: Jianyu Zhan <nasa4836@xxxxxxxxx>
---
 mm/memcontrol.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 80d9e38..46333cb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -528,10 +528,10 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
 static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
 {
 	/*
-	 * The ID of the root cgroup is 0, but memcg treat 0 as an
-	 * invalid ID, so we return (cgroup_id + 1).
+	 * The ID of css for the root cgroup is 0, but memcg treat 0 as an
+	 * invalid ID, so we return (id + 1).
 	 */
-	return memcg->css.cgroup->id + 1;
+	return css_to_id(&memcg->css) + 1;
 }
 
 static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
@@ -6407,7 +6407,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 	struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(css));
 
-	if (css->cgroup->id > MEM_CGROUP_ID_MAX)
+	if (css_to_id(css) > MEM_CGROUP_ID_MAX)
 		return -ENOSPC;
 
 	if (!parent)
-- 
2.0.0-rc0

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