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

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Date:	Thu, 14 Sep 2006 17:02:21 -0700
From:	Chandra Seetharaman <sekharan@...ibm.com>
To:	Pavel Emelianov <xemul@...nvz.org>
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)

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.

> 
> 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.
> 
> 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.

> 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

-- 

----------------------------------------------------------------------
    Chandra Seetharaman               | Be careful what you choose....
              - sekharan@...ibm.com   |      .......you may get it.
----------------------------------------------------------------------


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