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

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Date:	Fri, 13 Apr 2012 14:33:49 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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.

On 04/09/2012 11:37 PM, KAMEZAWA Hiroyuki wrote:
> (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.
> 

Kame,

Let me know what you think of the attached fix.
I still need to compile test it in other configs to be sure it doesn't
break, etc. But let's agree on it first.

View attachment "0001-decrement-static-keys-on-real-destroy-time.patch" of type "text/x-patch" (5325 bytes)