Re: [Xen-users] "dynamic memory allocation" for windows guests?

[Mike McClurg <mike.mcclurg@xxxxxxxxxx>]

On 10/02/13 13:44, Peter Gansterer wrote:
> On 2013-02-10 13:13:51 Mike McClurg wrote:
> > On 10/02/13 11:20, Peter Gansterer wrote:
> > > Hi again,
> > >
> > > Are there really no hints about this topic?
> > >
> > > It would also be useful to definitely know there is no solution
> > > for what we are looking for - or even input as to why this wouldn't work.
> > > Otherwise we'd think about trying it on our own.
> > You should look into the Xen Cloud Platform (XCP) [1], which has a
> > feature called Dynamic Memory Control, or memory ballooning [2]. It
> > requires you to install special PV drivers in your Windows guest. One of
> > these drivers is a ballooning daemon, which allocates a range of memory
> > from the guest OS, and then gives that memory back to Xen, which gives
> > the physical memory backed by that memory region to other guests. See
> > [2], "How do balloon drivers work and what is a memory balloon" for more
> > details.
> >
> > Mike
> >
> > [1] http://wiki.xen.org/wiki/XCP_Overview
> > [2] http://wiki.xen.org/wiki/Dynamic_Memory_Control
> Thx for the hint.
> I had a look at the docs; but from there it seems this is just an automatic way 
> to distribute memory targets when starting or stopping guests. As long as 
> guests don't change, memory config stays static.
> There is no hint, that memory targets are chosen according to the guests actual 
> requirements.
>
> I don't like the idea of seting up an XCP system just to confirm that this is 
> not what we're looking for.
>
> Maybe there is an XCP user on the list, who can tell me if DMC dynamically 
> changes memory targets according to requirements in the domU (even if no 
> machines are started or stopped)?
DMC allows you to change the memory targets of the guest while the guest 
is running, not just before the guest boots. It allows you to 
"overprovision" your system, so that the maximum amount of memory 
allocated to guests is greater than the total amount of physical memory 
on the system.
It does not dynamically change memory targets based on memory pressure 
in the guest (as mentioned in the DMC FAQ I referenced above). You'll 
probably have to roll your own custom solution for this.
If you would like to demo XCP without committing a physical box, you can 
run XCP inside a VM (it works on VirtualBox, Xen, and VMWare Player). 
Unfortunately, you can't run HVM guests inside a virtual XCP like this, 
only PV guests, so you won't be able to boot Windows guests inside your 
nested XCP system.
Mike


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