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

Tejun Heo
2013-06-13T19:53:09Z

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@huawei.com>
> Acked-by: Michal Hocko <mhocko@suse.cz>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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

But let's please remove the barrier dancing.

Thanks.

--
tejun