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20.19. Memory Balloon Device

A virtual memory balloon device is added to all Xen and KVM/QEMU guest virtual machines. It will be seen as <memballoon> element. It will be automatically added when appropriate, so there is no need to explicitly add this element in the guest virtual machine XML unless a specific PCI slot needs to be assigned. Note that if the memballoon device needs to be explicitly disabled, model='none' may be used.
The following example automatically added device with KVM 
  ...
  <devices>
    <memballoon model='virtio'/>
  </devices>
  ...
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Figure 20.67. Memory balloon device

Here is an example where the device is added manually with static PCI slot 2 requested 
  ...
  <devices>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </memballoon>
  </devices>
</domain>
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Figure 20.68. Memory balloon device added manually

The required model attribute specifies what type of balloon device is provided. Valid values are specific to the virtualization platform are: 'virtio' which is the default setting with the KVM hypervisor or 'xen' which is the default setting with the Xen hypervisor.
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