[PATCH v2] memcg: add mem_cgroup_from_css() helper

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

Changelog v2:
* fix too many args to mem_cgroup_from_css() (spotted by Kirill A. Shutemov)
* fix kernel build failed (spotted by Fengguang)

Add a mem_cgroup_from_css() helper to replace open-coded invokations of
container_of().  To clarify the code and to add a little more type safety.

Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>

---
 mm/memcontrol.c |   19 +++++++++++--------
 1 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 883283d..f0c7639 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -407,6 +407,12 @@ enum charge_type {
 static void mem_cgroup_get(struct mem_cgroup *memcg);
 static void mem_cgroup_put(struct mem_cgroup *memcg);
 
+static inline 
+struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
+{
+	return container_of(s, struct mem_cgroup, css);
+}
+
 /* Writing them here to avoid exposing memcg's inner layout */
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
 #include <net/sock.h>
@@ -864,9 +870,8 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
 
 struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
 {
-	return container_of(cgroup_subsys_state(cont,
-				mem_cgroup_subsys_id), struct mem_cgroup,
-				css);
+	return mem_cgroup_from_css(cgroup_subsys_state(cont,
+				mem_cgroup_subsys_id));
 }
 
 struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
@@ -879,8 +884,7 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
 	if (unlikely(!p))
 		return NULL;
 
-	return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
-				struct mem_cgroup, css);
+	return mem_cgroup_from_css(task_subsys_state(p, mem_cgroup_subsys_id));
 }
 
 struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
@@ -966,8 +970,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 		css = css_get_next(&mem_cgroup_subsys, id + 1, &root->css, &id);
 		if (css) {
 			if (css == &root->css || css_tryget(css))
-				memcg = container_of(css,
-						     struct mem_cgroup, css);
+				memcg = mem_cgroup_from_css(css);
 		} else
 			id = 0;
 		rcu_read_unlock();
@@ -2429,7 +2432,7 @@ static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
 	css = css_lookup(&mem_cgroup_subsys, id);
 	if (!css)
 		return NULL;
-	return container_of(css, struct mem_cgroup, css);
+	return mem_cgroup_from_css(css);
 }
 
 struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
-- 
1.7.7.6

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