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Date:   Sun, 29 Jul 2018 22:26:21 +0300
From:   Vladimir Davydov <vdavydov.dev@gmail.com>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Kirill Tkhai <ktkhai@virtuozzo.com>, cgroups@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on
 mem_cgroup_css_alloc() failure
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On Fri, Jul 27, 2018 at 03:31:34PM -0400, Johannes Weiner wrote:
> That said, the lifetime of the root reference on the ID is the online
> state, we put that in css_offline. Is there a reason we need to have
> the ID ready and the memcg in the IDR before onlining it?

I fail to see any reason for this in the code.

> Can we do something like this and not mess with the alloc/free
> sequence at all?

I guess so, and this definitely looks better to me.