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

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Date:	Fri, 15 Sep 2006 11:21:39 +0400
From:	Pavel Emelianov <xemul@...nvz.org>
To:	sekharan@...ibm.com
CC:	balbir@...ibm.com, Srivatsa <vatsa@...ibm.com>,
	Kirill Korotaev <dev@...ru>, Rik van Riel <riel@...hat.com>,
	CKRM-Tech <ckrm-tech@...ts.sourceforge.net>,
	Dave Hansen <haveblue@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>, Christoph Hellwig <hch@...radead.org>,
	Andrey Savochkin <saw@...ru>, devel@...nvz.org,
	Matt Helsley <matthltc@...ibm.com>,
	Hugh Dickins <hugh@...itas.com>,
	Alexey Dobriyan <adobriyan@...l.ru>,
	Oleg Nesterov <oleg@...sign.ru>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [ckrm-tech] [PATCH] BC: resource beancounters (v4) (added	user
 memory)

Chandra Seetharaman wrote:
> On Thu, 2006-09-14 at 17:02 +0400, Pavel Emelianov wrote:
>
> <snip>
>   
>> Reserving in advance means that sometimes you won't be able to start a
>> new group without taking back some of reserved pages. This is ... strange.
>>     
>
> I do not see it strange. At the time of creation, user sees the failure
> (that there isn't enough resource to provide the required/requested
> guarantee) and can act accordingly.
>
> BTW, VMware does it this way.
>   
And VPS density in VMware is MUCH lower than in
OpenVZ with beancounters :)
>   
>> I think that a satisfactory solution now would be:
>>  - limit unreclaimable memory during mmap() against soft limit to prevent
>>    potential rejects during page faults;
>>     
>
> we can have guarantee and still handle it this way.
>   
>>  - reclaim memory in case of hitting hard limit;
>>  - guarantees are done via setting soft and hard limits as I've shown
>> before.
>>     
>
> complexity is high in doing that.
>   
Nope. I've already said in another letter that a program of 60 lines
does this in a single loop.
>> The question still open is wether or not to account fractions.
>> I propose to skip fractions for a while and try to charge the page to
>> it's first user.
>>     
>
> sounds fine
>
>   
>> So final BC design is:
>> 1. three resources:
>>        - kernel memory
>>        - user unreclaimable memory
>>        - user reclaimable memory
>>     
>
> should be able to get other controllers also under this framework.
>   
OK. But note, that it's easy to add new resource to current BC code.
The most difficult thing is placing 'charge/uncharge' calls over the kernel.
>   
>> 2. unreclaimable memory is charged "in advance", reclaimable
>>    is charged "on demand" with reclamation if needed
>> 3. each object (kernel one or user page) is charged to the
>>    first user
>> 4. each resource controller declares it's own
>>        - meaning of "limit" parameter (percent/size/bandwidth/etc)
>>        - behaviour on changing limit (e.g. reclamation)
>>        - behaviour on hitting the limit (e.g. reclamation)
>> 5. BC can be assigned to any task by pid (not just current)
>>    without recharging currently charged resources.
>>     
>
> Please see the emails i sent earlier in this context:
> http://marc.theaimsgroup.com/?l=ckrm-tech&m=115593001810616&w=2
>
> We would need at least:
>  - BC should be created/deleted explicitly by the user
>  - cleaner interface for controller writers
>   
OK.
Next week we'll try to send a new set of patches.
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