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

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Message-ID: <20170117170215.GC28948@mtj.duckdns.org>
Date:   Tue, 17 Jan 2017 09:02:15 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Vladimir Davydov <vdavydov@...antool.org>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, akpm@...ux-foundation.org,
        jsvana@...com, hannes@...xchg.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, cgroups@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 2/9] slab: remove synchronous rcu_barrier() call in memcg
 cache release path

On Tue, Jan 17, 2017 at 08:37:45AM -0800, Tejun Heo wrote:
> 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.

Oh I was confusing synchronize_rcu() with rcu_barrier(), so you're
right, kmem_cache struct needs to stay around for the slab pages to be
freed after RCU grace period.  Will revise the patch accordingly,
thanks.

Thanks.

-- 
tejun