[v2 PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG

[Yang Shi <yang.shi@linux.alibaba.com>]

Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker:
make shrinker not depend on memcg kmem"), shrinkers' idr is protected by
CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to
protect shrinker idr replace with CONFIG_MEMCG_KMEM.

And, in CONFIG_MEMCG && CONFIG_SLOB case, shrinker_idr contains only
shrinker, and it is deferred_split_shrinker.  But it is never actually
called, since idr_replace() is never compiled due to the wrong #ifdef.
The deferred_split_shrinker all the time is staying in half-registered
state, and it's never called for subordinate mem cgroups.

Fixes: 0a432dcbeb32 ("mm: shrinker: make shrinker not depend on memcg kmem")
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: <stable@vger.kernel.org> 5.4+
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ee4eecc..e7f10c4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
 {
 	down_write(&shrinker_rwsem);
 	list_add_tail(&shrinker->list, &shrinker_list);
-#ifdef CONFIG_MEMCG_KMEM
+#ifdef CONFIG_MEMCG
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
 		idr_replace(&shrinker_idr, shrinker, shrinker->id);
 #endif
-- 
1.8.3.1