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

From	Tejun Heo <tj@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/9] slab: remove synchronous rcu_barrier() call in memcg cache release path
Date	2017-01-14 16:20 +0100
Message-ID	<sZyhz-7vW-3@gated-at.bofh.it> (permalink)
References	<sZpxE-2ag-3@gated-at.bofh.it> <sZpxE-2ag-13@gated-at.bofh.it> <sZwz8-6t0-13@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

Hello, Vladimir.

On Sat, Jan 14, 2017 at 04:19:39PM +0300, Vladimir Davydov wrote:
> 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?

Yeah, I had a similar question and scanned its users briefly.  Looks
like it's used in combination with ctors so that its users can
opportunistically dereference objects and e.g. check ids / state /
whatever without worrying about the objects' lifetimes.

Thanks.

-- 
tejun

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH 2/9] slab: remove synchronous rcu_barrier() call in memcg cache release path Tejun Heo <tj@kernel.org> - 2017-01-14 07:00 +0100
  Re: [PATCH 2/9] slab: remove synchronous rcu_barrier() call in memcg  cache release path Vladimir Davydov <vdavydov@tarantool.org> - 2017-01-14 14:30 +0100
    Re: [PATCH 2/9] slab: remove synchronous rcu_barrier() call in memcg  cache release path Tejun Heo <tj@kernel.org> - 2017-01-14 16:20 +0100

csiph-web