[libvirt] Virtio Ballon driver problem

Eric Blake eblake at redhat.com
Fri Dec 9 15:28:33 UTC 2011

On 12/09/2011 02:39 AM, Pankaj Rawat wrote:
> Hi .well I am trying to use virtioballon driver on my KVM host . I have
> assigned 400 MB current memory to my guest
> The ballon size is 600MB but when I used all the 400MB of guest the RAM
> of guest is not increasing.
> I watch the ram usage by running following command
> #free -m

Is that in the host or in the guest?

> But the guest is only using memory upto 400MB after that the process is
> killed .

Which process?  The guest process trying to use memory, or the host qemu
process running the guest?  Can you show actual transcripts of your
testing?  Assigning 400MiB current memory to the guest implies that the
balloon driver in the guest will prevent the guest from using more than
400MiB, even if the max allocation is higher.  The balloon driver in the
guest does not have the ability to dynamically request more memory from
the host, rather, balloon expansion or contraction is controlled by host

> I don't see the ballon driver coming into picture. It is not doing
> anything

On the host, did you use the 'virsh setmem' command (or other language
binding to access the virDomainSetMemory API), which is the documented
way to have the host request the guest to change the allocation consumed
by the guest's balloon driver?

> The ballon driver is loaded in host as well as guest

The balloon driver only matters in the guest; it is a guest device
designed for cooperation with host control.

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Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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