From: Tejun Heo <tj@kernel.org>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vladimir Davydov <vdavydov@tarantool.org>,
cl@linux.com, penberg@kernel.org, rientjes@google.com,
akpm@linux-foundation.org, jsvana@fb.com, hannes@cmpxchg.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
cgroups@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH 2/9] slab: remove synchronous rcu_barrier() call in memcg cache release path
Date: Tue, 17 Jan 2017 08:37:45 -0800 [thread overview]
Message-ID: <20170117163745.GA8352@mtj.duckdns.org> (raw)
In-Reply-To: <20170117000754.GA25218@js1304-P5Q-DELUXE>
Hello, Joonsoo.
On Tue, Jan 17, 2017 at 09:07:54AM +0900, Joonsoo Kim wrote:
> Long time no see! :)
Yeah, happy new year!
> IIUC, rcu_barrier() here prevents to destruct the kmem_cache until all
> slab pages in it are freed. These slab pages are freed through call_rcu().
Hmm... why do we need that tho? SLAB_DESTROY_BY_RCU only needs to
protect the slab pages, not kmem cache struct. I thought that this
was because kmem cache destruction is allowed to release pages w/o RCU
delaying it.
> Your patch changes it to another call_rcu() and, I think, if sequence of
> executing rcu callbacks is the same with sequence of adding rcu
> callbacks, it would work. However, I'm not sure that it is
> guaranteed by RCU API. Am I missing something?
The call sequence doesn't matter. Whether you're using call_rcu() or
rcu_barrier(), you're just waiting for a grace period to pass before
continuing. It doens't give any other ordering guarantees, so the new
code should be equivalent to the old one except for being asynchronous.
Thanks.
--
tejun
next prev parent reply other threads:[~2017-01-17 16:37 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-14 5:54 [PATCHSET] slab: make memcg slab destruction scalable Tejun Heo
2017-01-14 5:54 ` [PATCH 1/9] Revert "slub: move synchronize_sched out of slab_mutex on shrink" Tejun Heo
2017-01-14 5:54 ` [PATCH 2/9] slab: remove synchronous rcu_barrier() call in memcg cache release path Tejun Heo
2017-01-14 13:19 ` Vladimir Davydov
2017-01-14 15:19 ` Tejun Heo
[not found] ` <20170114151921.GA32693-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org>
2017-01-17 0:07 ` Joonsoo Kim
2017-01-17 16:37 ` Tejun Heo [this message]
2017-01-17 17:02 ` Tejun Heo
2017-01-14 5:54 ` [PATCH 3/9] slab: simplify shutdown_memcg_caches() Tejun Heo
2017-01-14 13:27 ` Vladimir Davydov
2017-01-14 15:38 ` Tejun Heo
2017-01-14 15:53 ` Tejun Heo
2017-01-14 5:54 ` [PATCH 4/9] slab: reorganize memcg_cache_params Tejun Heo
2017-01-14 13:30 ` Vladimir Davydov
2017-01-14 5:54 ` [PATCH 5/9] slab: link memcg kmem_caches on their associated memory cgroup Tejun Heo
2017-01-14 13:33 ` Vladimir Davydov
2017-01-14 5:54 ` [PATCH 6/9] slab: don't put memcg caches on slab_caches list Tejun Heo
2017-01-14 13:39 ` Vladimir Davydov
2017-01-14 15:39 ` Tejun Heo
2017-01-14 5:54 ` [PATCH 7/9] slab: introduce __kmemcg_cache_deactivate() Tejun Heo
2017-01-14 13:42 ` Vladimir Davydov
2017-01-14 15:39 ` Tejun Heo
2017-01-14 5:54 ` [PATCH 8/9] slab: remove synchronous synchronize_sched() from memcg cache deactivation path Tejun Heo
[not found] ` <20170114055449.11044-9-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2017-01-14 13:57 ` Vladimir Davydov
2017-01-14 5:54 ` [PATCH 9/9] slab: remove slub sysfs interface files early for empty memcg caches Tejun Heo
2017-01-14 14:00 ` Vladimir Davydov
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