linux-kernel - Re: [ckrm-tech] [PATCH] BC: resource beancounters (v4) (added user memory)

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Message-ID: <45051C0A.1060302@in.ibm.com>
Date:	Mon, 11 Sep 2006 13:49:22 +0530
From:	Balbir Singh <balbir@...ibm.com>
To:	Pavel Emelianov <xemul@...nvz.org>
Cc:	Dave Hansen <haveblue@...ibm.com>, Rik van Riel <riel@...hat.com>,
	Srivatsa <vatsa@...ibm.com>, sekharan@...ibm.com,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	CKRM-Tech <ckrm-tech@...ts.sourceforge.net>,
	Andi Kleen <ak@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrey Savochkin <saw@...ru>,
	Matt Helsley <matthltc@...ibm.com>,
	Hugh Dickins <hugh@...itas.com>,
	Alexey Dobriyan <adobriyan@...l.ru>,
	Kirill Korotaev <dev@...ru>, Oleg Nesterov <oleg@...sign.ru>,
	devel@...nvz.org
Subject: Re: [ckrm-tech] [PATCH] BC: resource beancounters (v4) (added	user
 memory)

Pavel Emelianov wrote:
> Balbir Singh wrote:
>> Pavel Emelianov wrote:
>>> Balbir Singh wrote:
>>>> Dave Hansen wrote:
>>>>> On Fri, 2006-09-08 at 11:33 +0400, Pavel Emelianov wrote:
>>>>>> I'm afraid we have different understandings of what a "guarantee" is.
>>>>> It appears so.
>>>>>
>>>>>> Don't we?
>>>>>> Guarantee may be one of
>>>>>>
>>>>>>   1. container will be able to touch that number of pages
>>>>>>   2. container will be able to sys_mmap() that number of pages
>>>>>>   3. container will not be killed unless it touches that number of
>>>>>> pages
>>>>> A "death sentence" guarantee?  I like it. :)
>>>>>
>>>>>>   4. anything else
>>>>>>
>>>>>> Let's decide what kind of a guarantee we want.
>>>> I think of guarantees w.r.t resources as the lower limit on the
>>>> resource.
>>>> Guarantees and limits can be thought of as the range (guarantee, limit]
>>>> for the usage of the resource.
>>>>
>>>>> I think of it as: "I will be allowed to use this many total pages, and
>>>>> they are guaranteed not to fail."  (1), I think.  The sum of all of
>>>>> the
>>>>> system's guarantees must be less than or equal to the amount of free
>>>>> memory on the machine. 
>>>> Yes, totally agree.
>>> Such a guarantee is really a limit and this limit is even harder than
>>> BC's one :)
>>>
>>> E.g. I have a node with 1Gb of ram and 10 containers with 100Mb
>>> guarantee each.
>>> I want to start one more. What shall I do not to break guarantees?
>> Don't start the new container or change the guarantees of the existing
>> ones
>> to accommodate this one :) The QoS design (done by the administrator)
>> should
>> take care of such use-cases. It would be perfectly ok to have a container
>> that does not care about guarantees to set their guarantee to 0 and set
>> their limit to the desired value. As Chandra has been stating we need two
>> parameters (guarantee, limit), either can be optional, but not both.
> If I set up 9 groups to have 100Mb limit then I have 100Mb assured (on
> 1Gb node)
> for the 10th one exactly. And I do not have to set up any guarantee as
> it won't affect
> anything. So what a guarantee parameter is needed for?

This use case works well for providing guarantee to one container. What if
I want guarantees of 100Mb and 200Mb for two containers? How do I setup
the system using limits?

Even I restrict everyone else to 700Mb. With this I cannot be sure that
the remaining 300Mb will be distributed as 100Mb and 200Mb.


-- 

	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs
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