Re: [PATCH 2/9] slab: remove synchronous rcu_barrier() call in memcg cache release path

Vladimir Davydov
2017-01-14T13:19:39Z

Hello Tejun,

Thanks a lot for looking into this issue as it seems to affect a lot of
users!

On Sat, Jan 14, 2017 at 12:54:42AM -0500, Tejun Heo wrote:
> This patch updates the cache release path so that it simply uses
> call_rcu() instead of the synchronous rcu_barrier() + custom batching.
> This doesn't cost more while being logically simpler and way more
> scalable.

The point of rcu_barrier() is to wait until all rcu calls freeing slabs
from the cache being destroyed are over (rcu_free_slab, kmem_rcu_free).
I'm not sure if call_rcu() guarantees that for all rcu implementations
too. If it did, why would we need rcu_barrier() at all?