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Date: Thu, 10 Aug 2017 12:34:06 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: memcg Can't context between v1 and v2 because css->refcnt not
 released
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To: wang Yu <yuwang668899@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>, cgroups@vger.kernel.org, linux-mm@kvack.org

[restoring the CC list]

On Thu 10-08-17 17:57:38, wang Yu wrote:
> 2017-08-10 17:28 GMT+08:00 wang Yu <yuwang668899@gmail.com>:
[...]
> > after drop caches, memory.stat  shows not pages belong the group, but
> > memory.usage_in_bytes not zero, so maybe other pages
> > has wrong to belong this group
>
> after drop cache, there maybe have kmem pages ,e.g. slab
> it can't free both drop cache or tasks free,
> so back this problem, without mem_cgroup_reparent_charges,
> cgroup v1 can't umount , and cgroup v2 can't mount

Ohh, right. It is true that there is no explicit control over kmem page
life time. I am afraid this is something non-trivial to address though.
I am not sure swithing between cgroup versions is a strong enough use
case to implement something like that but you can definitely try to do
that.
-- 
Michal Hocko
SUSE Labs

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