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

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Date:	Mon, 11 Sep 2006 12:42:05 -0700
From:	Chandra Seetharaman <sekharan@...ibm.com>
To:	rohitseth@...gle.com
Cc:	Rik van Riel <riel@...hat.com>, Srivatsa <vatsa@...ibm.com>,
	CKRM-Tech <ckrm-tech@...ts.sourceforge.net>, balbir@...ibm.com,
	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>,
	Pavel Emelianov <xemul@...nvz.org>
Subject: Re: [ckrm-tech] [PATCH] BC: resource beancounters (v4)
	(added	user	memory)

On Mon, 2006-09-11 at 12:10 -0700, Rohit Seth wrote:
> On Mon, 2006-09-11 at 11:25 -0700, Chandra Seetharaman wrote:
> > On Fri, 2006-09-08 at 14:43 -0700, Rohit Seth wrote:
> > <snip>
> > 
> > > > > 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
> > > > >   4. anything else
> > > > 
> > > > I would say (1) with slight modification
> > > >    "container will be able to touch _at least_ that number of pages"
> > > > 
> > > 
> > > Does this scheme support running of tasks outside of containers on the
> > > same platform where you have tasks running inside containers.  If so
> > > then how will you ensure processes running out side any container will
> > > not leave less than the total guaranteed memory to different containers.
> > > 
> > 
> > There could be a default container which doesn't have any guarantee or
> > limit. 
> 
> First, I think it is critical that we allow processes to run outside of
> any container (unless we know for sure that the penalty of running a
> process inside a container is very very minimal).

When I meant a default container I meant a default "resource group". In
case of container that would be the default environment. I do not see
any additional overhead associated with it, it is only associated with
how resource are allocated/accounted.

> 
> And anything running outside a container should be limited by default
> Linux settings.

note that the resource available to the default RG will be (total system
resource - allocated to RGs).
> 
> > When you create containers and assign guarantees to each of them
> > make sure that you leave some amount of resource unassigned. 
>                            ^^^^^ This will force the "default" container
> with limits (indirectly). IMO, the whole guarantee feature gets defeated

You _will_ have limits for the default RG even if we don't have
guarantees.

> the moment you bring in this fuzziness.

Not really. 
 - Each RG will have a guarantee and limit of each resource. 
 - default RG will have (system resource - sum of guarantees)
 - Every RG will be guaranteed some amount of resource to provide QoS
 - Every RG will be limited at "limit" to prevent DoS attacks.
 - Whoever doesn't care either of those set them to don't care values.

> 
> > That
> > unassigned resources can be used by the default container or can be used
> > by containers that want more than their guarantee (and less than their
> > limit). This is how CKRM/RG handles this issue.
> > 
> >  
> 
> It seems that a single notion of limit should suffice, and that limit
> should more be treated as something beyond which that resource
> consumption in the container will be throttled/not_allowed.

As I stated in an earlier email "Limit only" approach can prevent a
system from DoS attacks (and also fits the container model nicely),
whereas to provide QoS one would need guarantee.

Without guarantee, a RG that the admin cares about can starve if
all/most of the other RGs consume upto their limits.

> 
> -rohit
> 
> 
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-- 

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


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