netdev - Re: [BUGFIX][PATCH 3/3] memcg/tcp: ignore tcp usage before accounting started

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Date:	Wed, 4 Apr 2012 02:31:48 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	David Miller <davem@...emloft.net>
CC:	<kamezawa.hiroyu@...fujitsu.com>, <netdev@...r.kernel.org>,
	<akpm@...ux-foundation.org>
Subject: Re: [BUGFIX][PATCH 3/3] memcg/tcp: ignore tcp usage before accounting
 started

On 04/02/2012 07:41 AM, David Miller wrote:
> From: Glauber Costa<glommer@...allels.com>
> Date: Thu, 29 Mar 2012 11:21:07 +0200
>
>> On 03/29/2012 09:10 AM, KAMEZAWA Hiroyuki wrote:
>>> tcp memcontrol starts accouting after res->limit is set. So, if a sockets
>>> starts before setting res->limit, there are already used resource.
>>> After setting res->limit, the resource (already used) will be uncharged and
>>> make res_counter below 0 because they are not charged. This causes warning.
>>>
>>> This patch fixes that by adding res_counter_uncharge_nowarn().
>>> (*) We cannot avoid this while we have 'account start' switch.
>>>
>>> Signed-off-by: KAMEZAWA Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
>>
>> Fine by me.
>>
>> Acked-by: Glauber Costa<glommer@...allels.com>
>
> I'm not applying patches that simply ignore accounting counter
> underflows.
>
> You must either:
>
> 1) Integrate the socket's existing usage when the limit is set.
>
> 2) Avoid accounting completely for a socket that started before
>     the limit was set.
>
> No half-way solutions, please.  Otherwise it is impossible to design
> validations of the resource usage for a particular socket or group of
> sockets, because they can always be potentially "wrong" and over the
> limit.  That's a design for a buggy system.
>
>
Kame,

I agree with Dave FWIW.

We should be able to do this by dropping the reference count when the 
cgroup is finally destroyed, instead of from the remove callback. At 
that point, no more pending sockets should be attached to it.

Prior to increasing the static key, they are all assigned to the global 
cgroup, so we shouldn't care about them.
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