memcg: always create memsw files if CONFIG_CGROUP_MEM_RES_CTLR_SWAP

Instead of conditioning creation of memsw files on do_swap_account,
always create the files if compiled-in and fail read/write attempts
with -EOPNOTSUPP if !do_swap_account.

This is suggested by KAMEZAWA to simplify memcg file creation so that
it can use cgroup->subsys_cftypes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 31 insertions, 34 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7d698df4a067..97a45b392f77 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3879,14 +3879,21 @@ static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
         return val << PAGE_SHIFT;
 }
 
-static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
+static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
+                               struct file *file, char __user *buf,
+                               size_t nbytes, loff_t *ppos)
 {
         struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
+        char str[64];
         u64 val;
-        int type, name;
+        int type, name, len;
 
         type = MEMFILE_TYPE(cft->private);
         name = MEMFILE_ATTR(cft->private);
+
+        if (!do_swap_account && type == _MEMSWAP)
+                return -EOPNOTSUPP;
+
         switch (type) {
         case _MEM:
                 if (name == RES_USAGE)
@@ -3903,7 +3910,9 @@ static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
         default:
                 BUG();
         }
-        return val;
+
+        len = scnprintf(str, sizeof(str), "%llu\n", (unsigned long long)val);
+        return simple_read_from_buffer(buf, nbytes, ppos, str, len);
 }
 /*
  * The user of this function is...
@@ -3919,6 +3928,10 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
 
         type = MEMFILE_TYPE(cft->private);
         name = MEMFILE_ATTR(cft->private);
+
+        if (!do_swap_account && type == _MEMSWAP)
+                return -EOPNOTSUPP;
+
         switch (name) {
         case RES_LIMIT:
                 if (mem_cgroup_is_root(memcg)) { /* Can't set limit on root */
@@ -3984,12 +3997,15 @@ out:
 
 static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
 {
-        struct mem_cgroup *memcg;
+        struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
         int type, name;
 
-        memcg = mem_cgroup_from_cont(cont);
         type = MEMFILE_TYPE(event);
         name = MEMFILE_ATTR(event);
+
+        if (!do_swap_account && type == _MEMSWAP)
+                return -EOPNOTSUPP;
+
         switch (name) {
         case RES_MAX_USAGE:
                 if (type == _MEM)
@@ -4655,7 +4671,7 @@ static struct cftype mem_cgroup_files[] = {
         {
                 .name = "usage_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEM, RES_USAGE),
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
                 .register_event = mem_cgroup_usage_register_event,
                 .unregister_event = mem_cgroup_usage_unregister_event,
         },
@@ -4663,25 +4679,25 @@ static struct cftype mem_cgroup_files[] = {
                 .name = "max_usage_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEM, RES_MAX_USAGE),
                 .trigger = mem_cgroup_reset,
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
         },
         {
                 .name = "limit_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEM, RES_LIMIT),
                 .write_string = mem_cgroup_write,
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
         },
         {
                 .name = "soft_limit_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
                 .write_string = mem_cgroup_write,
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
         },
         {
                 .name = "failcnt",
                 .private = MEMFILE_PRIVATE(_MEM, RES_FAILCNT),
                 .trigger = mem_cgroup_reset,
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
         },
         {
                 .name = "stat",
@@ -4721,14 +4737,11 @@ static struct cftype mem_cgroup_files[] = {
                 .mode = S_IRUGO,
         },
 #endif
-};
-
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
-static struct cftype memsw_cgroup_files[] = {
         {
                 .name = "memsw.usage_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEMSWAP, RES_USAGE),
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
                 .register_event = mem_cgroup_usage_register_event,
                 .unregister_event = mem_cgroup_usage_unregister_event,
         },
@@ -4736,35 +4749,22 @@ static struct cftype memsw_cgroup_files[] = {
                 .name = "memsw.max_usage_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEMSWAP, RES_MAX_USAGE),
                 .trigger = mem_cgroup_reset,
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
         },
         {
                 .name = "memsw.limit_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEMSWAP, RES_LIMIT),
                 .write_string = mem_cgroup_write,
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
         },
         {
                 .name = "memsw.failcnt",
                 .private = MEMFILE_PRIVATE(_MEMSWAP, RES_FAILCNT),
                 .trigger = mem_cgroup_reset,
-                .read_u64 = mem_cgroup_read,
+                .read = mem_cgroup_read,
         },
-};
-
-static int register_memsw_files(struct cgroup *cont, struct cgroup_subsys *ss)
-{
-        if (!do_swap_account)
-                return 0;
-        return cgroup_add_files(cont, ss, memsw_cgroup_files,
-                                ARRAY_SIZE(memsw_cgroup_files));
-};
-#else
-static int register_memsw_files(struct cgroup *cont, struct cgroup_subsys *ss)
-{
-        return 0;
-}
 #endif
+};
 
 static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
 {
@@ -5047,9 +5047,6 @@ static int mem_cgroup_populate(struct cgroup_subsys *ss,
                                 ARRAY_SIZE(mem_cgroup_files));
 
         if (!ret)
-                ret = register_memsw_files(cont, ss);
-
-        if (!ret)
                 ret = register_kmem_files(cont, ss);
 
         return ret;