Re: [Xen-users] Xen live migration dom0 memory

[Alexander Hämmerle <Alexander.Haemmerle@xxxxxxxxxxxx>]

On 07/01/2015 04:30 PM, Ian Campbell wrote:
> On Wed, 2015-07-01 at 16:20 +0200, Epiontis IT wrote:
> > Hello,
> >
> > I'm new to XEN live migration. I have a question regarding XEN memory
> > management while doing a vm live migration. I observed that migrating a
> > vm on XEN 4.5.1 and Linux Kernel 4.1.0 requires the dom0 on the target
> > machine to have memory available that is the size of the memory
> > allocated to the vm (2G). Since I follow "XEN best practices" and set
> > dom0_mem to 512M the target machine begins swapping out 2G to disk which
> > makes everything nearly unresponsive. Is this requirement for the dom0
> > memory size intended or might there be an issue with my setup?
> I don't think you should need 2G dom0 memory, you should need 2G of free
> host memory.
>
> Perhaps something on your destination host is thinking it wants to
> balloon dom0 down in order to make that free host memory available?
>
> Ian.
I started out with only one vm running on the sending host, none on the 
destination host. Both hosts have dom_0=512M and 32GB free memory for 
the vms, autoballooning=0 is set in xl.conf. As soon as I do a "xl 
migrate" the destination host begins swapping out 2GB to disk. In an 
earlier setup I had XEN 4.4.1 and Linux 3.18 running and never observed 
any swapping as far as I could tell. So from your comment I conclude 
that there is some problem with my setup and dom0 doesn't need the vm 
memory size available for doing the migration.
Thanks,
Alexander

--
Alexander Hämmerle

Epiontis GmbH
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