Message-Id: <1158105253.4800.20.camel@linuxchandra>
Date:	Tue, 12 Sep 2006 16:54:13 -0700
From:	Chandra Seetharaman <sekharan@...ibm.com>
To:	rohitseth@...gle.com
Cc:	Rik van Riel <riel@...hat.com>, Srivatsa <vatsa@...ibm.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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>,
	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, Pavel Emelianov <xemul@...nvz.org>
Subject: Re: [ckrm-tech] [PATCH] BC: resource beancounters
	(v4)	(added	user	memory)

On Mon, 2006-09-11 at 16:58 -0700, Rohit Seth wrote:
> On Mon, 2006-09-11 at 12:42 -0700, Chandra Seetharaman wrote:
> > On Mon, 2006-09-11 at 12:10 -0700, Rohit Seth wrote:
> > > On Mon, 2006-09-11 at 11:25 -0700, Chandra Seetharaman wrote:
> 
> > > > 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.
> > 
> 
> There should be some cost when you do atomic inc/dec accounting and
> locks for add/remove resources from any container (including default
> resource group). No?

yes, it would be there, but is not heavy, IMO.
> 
> > > 
> > > 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).
> 
> I think it will be preferable to not change the existing behavior for
> applications that are running outside any container (in your case
> default resource group).

hmm, when you provide QoS for a set of apps, you will affect (the
resource availability of) other apps. I don't see any way around it. Any
ideas ?
 
> 
> > > 
> > > > 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.
> > 
> 
> For the cases that put this don't care, do you depend on existing
> reclaim algorithm (for memory) in kernel?

Yes.
> 
> > > 
> > > > 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.
> > 
> > > 
> 
> If the limits are set appropriately so that containers total memory
> consumption does not exceed the system memory then there shouldn't be
> any QoS issue (to whatever extent it is applicable for specific
> scenario).

Then you will not be work-conserving (IOW over-committing), which is one
of the main advantage of this type of feature.

> 
> -rohit
> 
> 
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-- 

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


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