[PATCH] mm/slab: fix kmemcg cache creation delayed issue

From: js1304
Date: Thu Oct 06 2016 - 02:21:03 EST

From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

There is a bug report that SLAB makes extreme load average due to
over 2000 kworker thread.


This issue is caused by kmemcg feature that try to create new set of
kmem_caches for each memcg. Recently, kmem_cache creation is slowed by
synchronize_sched() and futher kmem_cache creation is also delayed
since kmem_cache creation is synchronized by a global slab_mutex lock.
So, the number of kworker that try to create kmem_cache increases quitely.
synchronize_sched() is for lockless access to node's shared array but
it's not needed when a new kmem_cache is created. So, this patch
rules out that case.

Fixes: 801faf0db894 ("mm/slab: lockless decision to grow cache")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Doug Smythies <dsmythies@xxxxxxxxx>
Tested-by: Doug Smythies <dsmythies@xxxxxxxxx>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
mm/slab.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index 6508b4d..3c83c29 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -961,7 +961,7 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep,
* guaranteed to be valid until irq is re-enabled, because it will be
* freed after synchronize_sched().
- if (force_change)
+ if (old_shared && force_change)