Messages in this thread | | | Subject | Re: [ckrm-tech] [PATCH] BC: resource beancounters (v4) (added user memory) | From | Rohit Seth <> | Date | Tue, 12 Sep 2006 17:39:08 -0700 |
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On Tue, 2006-09-12 at 16:54 -0700, Chandra Seetharaman wrote: > 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.
I think anything greater than 1% could be a concern for people who are not very interested in containers but would be forced to live with them.
> > > > > > > > > > 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 I say, existing behavior, I mean not getting impacted by some artificial limits that are imposed by container subsystem. IOW, if a sysadmin is okay to have certain apps running outside of container then he is basically forgoing any QoS for any container on that system.
> > > > > > > > > > > > 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.
So one container with these don't care condition(s) can turn the whole guarantee thing bad. Because existing kernel reclaimer does not know about memory commitments to other containers. Right?
> > > > > > > > > > > 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. >
If for the systems where QoS is important, not over-committing will be fine (at least to start with).
-rohit
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