From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Tejun Heo <tj@kernel.org>
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 09:07:54 +0900 [thread overview]
Message-ID: <20170117000754.GA25218@js1304-P5Q-DELUXE> (raw)
In-Reply-To: <20170114151921.GA32693@mtj.duckdns.org>
On Sat, Jan 14, 2017 at 10:19:21AM -0500, Tejun Heo wrote:
> 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.
Hello, Tejun.
Long time no see! :)
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().
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?
Thanks.
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next prev parent reply other threads:[~2017-01-17 0:02 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
2017-01-17 0:07 ` Joonsoo Kim [this message]
2017-01-17 16:37 ` Tejun Heo
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
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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