Re: [Xen-devel] [PATCH 2/4] libxc: report how much memory a domain has on each NUMA node

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On mar, 2014-03-11 at 11:15 +0000, Ian Jackson wrote:
> Dario Faggioli writes ("Re: [Xen-devel] [PATCH 2/4] libxc: report how much 
> memory a domain has on each NUMA node"):
> > If something changed, then yes you're screwed, but the bottom line, I
> > think is, if you think you may need the information broken down in
> > nodes, use XEN_DOMCTL_domain_numainfo, which gives you that and,
> > indirectly, also the total size.
> 
> But it gives you for only one domain; whereas the domain list gives
> you all domains at once.
> 
Right. Not sure what you're after (see below), but yes, it's probably at
least a more accurate snapshot of the system... I'll try to move this in
dominfo.

> We have had problems before with toolstack memory balancing and
> managemetn algorithms needing information which wasn't properly
> available.  So I think I want to see an explanation how this would be
> used in an actual memory balancing/assignment algorith.
> 
I'm not sure why you're asking this. For now, this is not going to be
used in any algorithm, it's pure information reporting.

Of course, the system administrator, or a toolstack at an higher level
than libxl, can use the info for making some decisions, but then full
consistency is up to then, I guess... mostly because I don't think there
is much we can do.

In the current NUMA placement implementation, in libxl, what we need to
know is how much memory is free on each node, rather than how much
memory each domain occupies there.

So, what is it that I should try to show you?

Thanks and Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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