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

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Message-Id: <1158277364.6357.33.camel@linuxchandra>
Date:	Thu, 14 Sep 2006 16:42:44 -0700
From:	Chandra Seetharaman <sekharan@...ibm.com>
To:	Pavel Emelianov <xemul@...nvz.org>
Cc:	balbir@...ibm.com, Srivatsa <vatsa@...ibm.com>,
	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>,
	Kirill Korotaev <dev@...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 11:53 +0400, Pavel Emelianov wrote:

<snip>

> > What if I have 40 containers each with 2% guarantee ? what do we do
> > then ? and many other different combinations (what I gave was not the
> > _only_ scenario).
> >   
> Then you need to solve a set of 40 equations. This sounds weird, but
> don't afraid - sets like these are solved lightly.

extrapolate that to a varying # of permutations and real time changes in
the system workload. Won't it be complex ?

Wouldn't it be a lot simpler if we have the guarantee support instead ?
Why you do not like guarantee ? :)

<snip>

> >> Then how do you make sure that memory WILL be available when the group needs
> >> it without limiting the others in a proper way?
> >>     
> >
> > You could limit others only if you _know_ somebody is not getting what
> > they are supposed to get (based on guarantee).
> >   
> I don't understand your idea. Limit does _not_ imply anything - it's
> just a limit.

I didn't mean "limit" as defined in BC. I meant it in the generic sense.
IOW, if we have to provide guarantees then it would limit other RGs from
getting that (amount of guaranteed) resource.
 
> You may limit anything to anyone w/o bothering the consequences.
> Guarantee implies that the resource you guarantee will be available and
> this "will be" is something not that easy.
> 
> So I repeat my question - how can you be sure that these X megabytes you
> guarantee to some group won't be used by others so that you won't be able
> to reclaim them?

It depends on how the memory controller is implemented. It could be
implemented in different ways:
 - reclamation path will _not_ free pages belonging to a RG that is 
   below its guarantee.
 - allocation from a "over guarantee" RG can succeed iff there is
   memory after satisfying all guarantees (or will free pages from the
   requesting RG before it will succeed).
 - ...

BTW, my point is to have guarantees for _all_ resources not just memory.

> 
> 
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-- 

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


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