When we call __kmem_cache_shrink on memory cgroup removal, we need to
synchronize kmem_cache->cpu_partial update with put_cpu_partial that
might be running on other cpus. Currently, we achieve that by using
kick_all_cpus_sync, which works as a system wide memory barrier. Though
fast it is, this method has a flow - it issues a lot of IPIs, which
might hurt high performance or real-time workloads.
To fix this, let's replace kick_all_cpus_sync with synchronize_sched.
Although the latter one may take much longer to finish, it shouldn't be
a problem in this particular case, because memory cgroups are destroyed
asynchronously from a workqueue so that no user visible effects should
be introduced. OTOH, it will save us from excessive IPIs when someone
removes a cgroup.
Anyway, even if using synchronize_sched turns out to take too long, we
can always introduce a kind of __kmem_cache_shrink batching so that this
method would only be called once per one cgroup destruction (not per
each per memcg kmem cache as it is now).
Reported-and-suggested-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Vladimir Davydov <vdavy...@virtuozzo.com>
---
mm/slub.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/slub.c b/mm/slub.c
index 279e773d80d3..03067f43dcf4 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3697,7 +3697,7 @@ int __kmem_cache_shrink(struct kmem_cache *s, bool
deactivate)
* s->cpu_partial is checked locklessly (see put_cpu_partial),
* so we have to make sure the change is visible.
*/
- kick_all_cpus_sync();
+ synchronize_sched();
}
flush_all(s);
--
2.1.4
