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

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Message-ID: <4F823443.9070908@jp.fujitsu.com>
Date:	Mon, 09 Apr 2012 09:58:43 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [BUGFIX][PATCH 3/3] memcg/tcp: ignore tcp usage before accounting
 started

(2012/04/04 7:31), Glauber Costa wrote:

> 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.
> 

Could you do the fix ?

Thanks,
-Kame


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