mm: memcg: convert numa stat to read_seq_string interface

Instead of using the raw seq_file file interface, switch over to the
read_seq_string cftype callback and let cgroup core code set up the
seq_file.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Ying Han <yinghan@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -4128,12 +4128,12 @@ mem_cgroup_get_total_stat(struct mem_cgroup *memcg, struct mcs_total_stat *s)
 }
 
 #ifdef CONFIG_NUMA
-static int mem_control_numa_stat_show(struct seq_file *m, void *arg)
+static int mem_control_numa_stat_show(struct cgroup *cont, struct cftype *cft,
+				      struct seq_file *m)
 {
 	int nid;
 	unsigned long total_nr, file_nr, anon_nr, unevictable_nr;
 	unsigned long node_nr;
-	struct cgroup *cont = m->private;
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
 
 	total_nr = mem_cgroup_nr_lru_pages(memcg, LRU_ALL);
@@ -4608,22 +4608,6 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
 	return 0;
 }
 
-#ifdef CONFIG_NUMA
-static const struct file_operations mem_control_numa_stat_file_operations = {
-	.read = seq_read,
-	.llseek = seq_lseek,
-	.release = single_release,
-};
-
-static int mem_control_numa_stat_open(struct inode *unused, struct file *file)
-{
-	struct cgroup *cont = file->f_dentry->d_parent->d_fsdata;
-
-	file->f_op = &mem_control_numa_stat_file_operations;
-	return single_open(file, mem_control_numa_stat_show, cont);
-}
-#endif /* CONFIG_NUMA */
-
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
 static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
 {
@@ -4711,8 +4695,7 @@ static struct cftype mem_cgroup_files[] = {
 #ifdef CONFIG_NUMA
 	{
 		.name = "numa_stat",
-		.open = mem_control_numa_stat_open,
-		.mode = S_IRUGO,
+		.read_seq_string = mem_control_numa_stat_show,
 	},
 #endif
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP