netdev - Re: [PATCH] memcg/tcp: fix warning caused b res->usage go to negative.

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Date:	Tue, 10 Apr 2012 11:37:37 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
CC:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] memcg/tcp: fix warning caused b res->usage go to negative.

(2012/04/07 0:49), Glauber Costa wrote:

> On 03/30/2012 05:44 AM, KAMEZAWA Hiroyuki wrote:
>> Maybe what we can do before lsf/mm summit will be this (avoid warning.)
>> This patch is onto linus's git tree. Patch description is updated.
>>
>> Thanks.
>> -Kame
>> ==
>>  From 4ab80f84bbcb02a790342426c1de84aeb17fcbe9 Mon Sep 17 00:00:00 2001
>> From: KAMEZAWA Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
>> Date: Thu, 29 Mar 2012 14:59:04 +0900
>> Subject: [PATCH] memcg/tcp: fix warning caused b res->usage go to negative.
>>
>> tcp memcontrol starts accouting after res->limit is set. So, if a sockets
>> starts before setting res->limit, there are already used resource.
>> At setting res->limit, accounting starts. The resource will be uncharged
>> and make res_counter below 0 because they are not charged.
>> This causes warning.
>>
> 
> Kame,
> 
> Please test the following patch and see if it fixes your problems (I
> tested locally, and it triggers me no warnings running the test script
> you provided + an inbound scp -r copy of an iso directory from a remote
> machine)
> 
> When you are reviewing, keep in mind that we're likely to have the same
> problems with slab jump labels - since the slab pages will outlive the
> cgroup as well, and it might be worthy to keep this in mind, and provide
> a central point for the jump labels to be set of on cgroup destruction.
> 


Hm. What happens in following sequence ?

  1. a memcg is created
  2. put a task into the memcg, start tcp steam
  3. set tcp memory limit

The resource used between 2 and 3 will cause the problem finally.

Then, Dave's request
==
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.
==
are not satisfied. So, we need to have a state per sockets, it's accounted
or not. I'll look into this problem again, today.


Thanks,
-Kame









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