memcg: use css_get/put for swap memcg

Use css_get/put instead of mem_cgroup_get/put.  A simple replacement
will do.

The historical reason that memcg has its own refcnt instead of always
using css_get/put, is that cgroup couldn't be removed if there're still
css refs, so css refs can't be used as long-lived reference.  The
situation has changed so that rmdir a cgroup will succeed regardless css
refs, but won't be freed until css refs goes down to 0.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Glauber Costa <glommer@openvz.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 10 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bdc9582585af..76c0c99b002f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4231,12 +4231,12 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
         unlock_page_cgroup(pc);
         /*
          * even after unlock, we have memcg->res.usage here and this memcg
-         * will never be freed.
+         * will never be freed, so it's safe to call css_get().
          */
         memcg_check_events(memcg, page);
         if (do_swap_account && ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT) {
                 mem_cgroup_swap_statistics(memcg, true);
-                mem_cgroup_get(memcg);
+                css_get(&memcg->css);
         }
         /*
          * Migration does not charge the res_counter for the
@@ -4348,7 +4348,7 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
 
         /*
          * record memcg information,  if swapout && memcg != NULL,
-         * mem_cgroup_get() was called in uncharge().
+         * css_get() was called in uncharge().
          */
         if (do_swap_account && swapout && memcg)
                 swap_cgroup_record(ent, css_id(&memcg->css));
@@ -4379,7 +4379,7 @@ void mem_cgroup_uncharge_swap(swp_entry_t ent)
                 if (!mem_cgroup_is_root(memcg))
                         res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
                 mem_cgroup_swap_statistics(memcg, false);
-                mem_cgroup_put(memcg);
+                css_put(&memcg->css);
         }
         rcu_read_unlock();
 }
@@ -4413,11 +4413,14 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
                  * This function is only called from task migration context now.
                  * It postpones res_counter and refcount handling till the end
                  * of task migration(mem_cgroup_clear_mc()) for performance
-                 * improvement. But we cannot postpone mem_cgroup_get(to)
-                 * because if the process that has been moved to @to does
-                 * swap-in, the refcount of @to might be decreased to 0.
+                 * improvement. But we cannot postpone css_get(to)  because if
+                 * the process that has been moved to @to does swap-in, the
+                 * refcount of @to might be decreased to 0.
+                 *
+                 * We are in attach() phase, so the cgroup is guaranteed to be
+                 * alive, so we can just call css_get().
                  */
-                mem_cgroup_get(to);
+                css_get(&to->css);
                 return 0;
         }
         return -EINVAL;
@@ -6718,6 +6721,7 @@ static void __mem_cgroup_clear_mc(void)
 {
         struct mem_cgroup *from = mc.from;
         struct mem_cgroup *to = mc.to;
+        int i;
 
         /* we must uncharge all the leftover precharges from mc.to */
         if (mc.precharge) {
@@ -6738,7 +6742,9 @@ static void __mem_cgroup_clear_mc(void)
                 if (!mem_cgroup_is_root(mc.from))
                         res_counter_uncharge(&mc.from->memsw,
                                                 PAGE_SIZE * mc.moved_swap);
-                __mem_cgroup_put(mc.from, mc.moved_swap);
+
+                for (i = 0; i < mc.moved_swap; i++)
+                        css_put(&mc.from->css);
 
                 if (!mem_cgroup_is_root(mc.to)) {
                         /*
@@ -6748,7 +6754,7 @@ static void __mem_cgroup_clear_mc(void)
                         res_counter_uncharge(&mc.to->res,
                                                 PAGE_SIZE * mc.moved_swap);
                 }
-                /* we've already done mem_cgroup_get(mc.to) */
+                /* we've already done css_get(mc.to) */
                 mc.moved_swap = 0;
         }
         memcg_oom_recover(from);