Re: [Xen-users] How does live relocation work in xen 3.1?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> As key features of xen 3.1,live relocation and dynamic memory control
> enables dynamic resource scheduling and "no-downtime maintenance" of
> Microsoft Windows-based virtual infrastructures.
> I'm interested in how it works. I try to use the commands "xm mem-set" ,"xm
> list" and "xm top",but it seems of no use. The fullvirtualized windows
> guest still maintains the initial maximum memory.

Full virt guests can't communicate with Xen (unless you install Xen-aware 
drivers in them... see below), so they won't adjust their memory footprint in 
response to xm mem-set.

Since Xen 3.1 it has been possible, in principle, for a HVM guest to support 
memory ballooning.  However, the Windows drivers for this (if they're 
available yet) will be part of the various flavours of XenEnterprise (or 
similar drivers may be available in Novell's Windows Xen drivers).

> However,those commands 
> take effect in domain 0.So I think it will also take effect in
> paravirtualized guests.Am I right?

Yes, well deduced.  If you want to reduce a domain and force it to *stay* 
reduced you should use xm mem-max after mem-set to change the maximum memory 
footprint the domain may have.

Remember that to enlarge a guest beyond it's initial allocation you first need 
to use xm mem-max to make sure that Xen will allow it to grow.  And guests 
won't be able to enlarge their allocation unless they build a large enough 
memory map at bootup, so you want to tell them how big it should be on the 
kernel command line.  I think the parameter is "mem=" so "mem=4G" creates a 
guest that is able to grow up to 4G in total size, if you request it.

> Is there anyone who can tell me how the features work in fullvirtualized
> windows guest? Many thanks.

You might be able to get this stuff working in an HVM Linux guest right now 
using the paravirtualised drivers available.  However, you won't be able to 
do the same in Windows unless you use a solution that supports PV drivers 
under Windows.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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