linux-kernel - Re: [PATCH cgroup/for-4.4-fixes 2/3] cgroup: fix handling of multi-destination migration from subtree

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Date:	Thu, 3 Dec 2015 10:16:32 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>,
	Daniel Wagner <daniel.wagner@...-carit.de>
Cc:	Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, Dave Jones <davej@...emonkey.org.uk>,
	kernel-team@...com, Aleksa Sarai <cyphar@...har.com>,
	Michal Hocko <mhocko@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH cgroup/for-4.4-fixes 2/3] cgroup: fix handling of
 multi-destination migration from subtree_control enabling

On Mon, Nov 30, 2015 at 05:44:31PM -0500, Tejun Heo wrote:
> From 0d7d444e260493252e30c70813c7657e9ede2f12 Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@...nel.org>
> Date: Mon, 30 Nov 2015 17:24:34 -0500
> 
> Consider the following v2 hierarchy.
> 
>   P0 (+memory) --- P1 (-memory) --- A
>                                  \- B
> 
> P0 has memory enabled in its subtree_control while P1 doesn't.  If
> both A and B contain processes, they would belong to the memory css of
> P1.  Now if memory is enabled on P1's subtree_control, memory csses
> should be created on both A and B and A's processes should be moved to
> the former and B's processes the latter.  IOW, enabling controllers
> can cause atomic migrations into different csses.
> 
> The core cgroup migration logic has been updated accordingly but the
> controller migration methods haven't and still assume that all tasks
> migrate to a single target css; furthermore, the methods were fed the
> css in which subtree_control was updated which is the parent of the
> target csses.  pids controller depends on the migration methods to
> move charges and this made the controller attribute charges to the
> wrong csses often triggering the following warning by driving a
> counter negative.

Applying 1-2 to libata/for-4.4-fixes.

Thanks.

-- 
tejun
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