linux-kernel - Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging kmem

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Date:	Thu, 13 Jun 2013 12:53:00 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Glauber Costa <glommer@...allels.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging
 kmem

On Thu, Jun 13, 2013 at 05:12:55PM +0800, Li Zefan wrote:
> Sorry for updating the patchset so late.
> 
> I've made some changes for the memory barrier thing, and I agree with
> Michal that there can be improvement but can be a separate patch.
> 
> If this version is ok for everyone, I'll send the whole patchset out
> to Andrew.

Can you please post an updated patch as reply to the original patch?
It's a bit difficult to follow things.

> =========================
> 
> Use css_get/put instead of mem_cgroup_get/put.
> 
> We can't do a simple replacement, because here mem_cgroup_put()
> is called during mem_cgroup_css_free(), while mem_cgroup_css_free()
> won't be called until css refcnt goes down to 0.
> 
> Instead we increment css refcnt in mem_cgroup_css_offline(), and
> then check if there's still kmem charges. If not, css refcnt will
> be decremented immediately, otherwise the refcnt won't be decremented
> when kmem charges goes down to 0.
> 
> v3:
> - changed wmb() to smp_smb(), and moved it to memcg_kmem_mark_dead(),
>   and added comment.
> 
> v2:
> - added wmb() in kmem_cgroup_css_offline(), pointed out by Michal
> - revised comments as suggested by Michal
> - fixed to check if kmem is activated in kmem_cgroup_css_offline()
> 
> Signed-off-by: Li Zefan <lizefan@...wei.com>
> Acked-by: Michal Hocko <mhocko@...e.cz>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Reviewed-by: Tejun Heo <tj@...nel.org>

But let's please remove the barrier dancing.

Thanks.

-- 
tejun
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