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

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Message-Id: <20120401.234113.1505269982606203786.davem@davemloft.net>
Date:	Sun, 01 Apr 2012 23:41:13 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	glommer@...allels.com
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

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.


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