linux-kernel - Re: [PATCH -mm v2 3/8] memcg: mark caches that belong to offline memcgs as dead

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Date:	Tue, 10 Jun 2014 14:06:31 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	<akpm@...ux-foundation.org>, <cl@...ux.com>, <rientjes@...gle.com>,
	<penberg@...nel.org>, <hannes@...xchg.org>, <mhocko@...e.cz>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH -mm v2 3/8] memcg: mark caches that belong to offline
 memcgs as dead

On Tue, Jun 10, 2014 at 04:48:40PM +0900, Joonsoo Kim wrote:
> On Fri, Jun 06, 2014 at 05:22:40PM +0400, Vladimir Davydov wrote:
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 886b5b414958..ed42fd1105a5 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -3294,6 +3294,7 @@ static void memcg_unregister_all_caches(struct mem_cgroup *memcg)
> >  	mutex_lock(&memcg_slab_mutex);
> >  	list_for_each_entry_safe(params, tmp, &memcg->memcg_slab_caches, list) {
> >  		cachep = memcg_params_to_cache(params);
> > +		cachep->memcg_params->dead = true;
> 
> I guess that this needs smp_wmb() and memcg_cache_dead() needs
> smp_rmb(), since we could call memcg_cache_dead() without holding any locks.

Good catch! Actually, I thought we always call on_each_cpu, which works
effectively as a full memory barrier, from kmem_cache_shrink, but that's
not always true for SLUB, so we do need the barriers here. Will fix in
the next iteration.

Thanks.
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