memcg: add mem_cgroup_from_css() helper

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.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Gavin Shan <shangw@linux.vnet.ibm.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2ac431620051f2f97fb8600219d254362fa39402..3fdd00a2d73126f5f5cc482eae014388eed44dcd 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -411,6 +411,12 @@ static void mem_cgroup_put(struct mem_cgroup *memcg);
 #include <net/sock.h>
 #include <net/ip.h>
 
+static inline
+struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
+{
+       return container_of(s, struct mem_cgroup, css);
+}
+
 static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
 void sock_update_memcg(struct sock *sk)
 {
@@ -863,7 +869,7 @@ 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,
+       return mem_cgroup_from_css(cgroup_subsys_state(cont,
                                mem_cgroup_subsys_id), struct mem_cgroup,
                                css);
 }
@@ -878,7 +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),
+       return mem_cgroup_from_css(task_subsys_state(p, mem_cgroup_subsys_id),
                                struct mem_cgroup, css);
 }
 
@@ -965,7 +971,7 @@ 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,
+                               memcg = mem_cgroup_from_css(css,
                                                     struct mem_cgroup, css);
                } else
                        id = 0;
@@ -2495,7 +2501,7 @@ 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, css);
 }
 
 struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)