linux-kernel - Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css

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Message-ID: <20180801161626.j2575eru2x3lukfj@esperanza>
Date:   Wed, 1 Aug 2018 19:16:26 +0300
From:   Vladimir Davydov <vdavydov.dev@...il.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on
 mem_cgroup_css_alloc() failure

On Mon, Jul 30, 2018 at 11:31:13AM -0400, Johannes Weiner wrote:
> On Sun, Jul 29, 2018 at 10:26:21PM +0300, Vladimir Davydov wrote:
> > 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.
> 
> Me neither, thanks for double checking.
> 
> The patch also survives stress testing cgroup creation and destruction
> with the script from 73f576c04b94 ("mm: memcontrol: fix cgroup
> creation failure after many small jobs").
> 
> > > 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.
> 
> Cool, then I think we should merge Kirill's patch as the fix and mine
> as a follow-up cleanup.
> 
> ---
> 
> From b4106ea1f163479da805eceada60c942bd66e524 Mon Sep 17 00:00:00 2001
> From: Johannes Weiner <hannes@...xchg.org>
> Date: Mon, 30 Jul 2018 11:03:55 -0400
> Subject: [PATCH] mm: memcontrol: simplify memcg idr allocation and error
>  unwinding
> 
> The memcg ID is allocated early in the multi-step memcg creation
> process, which needs 2-step ID allocation and IDR publishing, as well
> as two separate IDR cleanup/unwind sites on error.
> 
> Defer the IDR allocation until the last second during onlining to
> eliminate all this complexity. There is no requirement to have the ID
> and IDR entry earlier than that. And the root reference to the ID is
> put in the offline path, so this matches nicely.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Vladimir Davydov <vdavydov.dev@...il.com>