virt-manager GUI fails to allocate more than 32GB memory to VM

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6 + earlier virt-manager-0.8.6-4.el6
  • Virt-Manager
  • KVM and XEN

Issue

  • Why virt-manager GUI fails to allocate memory above 32GB for VM based on kvm?
  • How much memory can be allocated to KVM guest through virt-manager?
  • Virtualization limits page says KVM guest supports up to 512 GB of memory but virt-manager failed to allocate more than 32G memory to fully virtualized KVM guest.

Resolution

For KVM

  • Add/extend the guest memory manually by editing guest XML config file.
  • Stop the Virtual Machine
  • Run the following command to edit the XML definitions of VM

#virsh edit

  • For example (here, <memory> is the "setmaxmem" value and <currentMemory> is the "setmem" value):
virsh # edit <domain-name>
<domain type='kvm'>
 ...
<memory>514144</memory>
<currentMemory>262144</currentMemory>
...
</domain>
  • Change the memory value as per your requirement and save the configuration.
  • Restart the libvirtd service

For XEN

  • Edit the guest file xml located under /etc/xen/

  • example:

            maxmem = 512   <-- These are the parameters which need to be modified. It is mentioned in MB
        memory = 512    <-- So for 32 GB mention 32000

    Restart the libvirtd service

  • This issue is fixed in Red Hat Enterprise Linux 6 with virt-manager-0.8.6-4.el6 (Bugzilla 640781)

Root Cause

  • Virt-manager has some limitation of maximum memory configuration in GUI.
  • It is not possible to allocate more then 32GB memory to VM through virt-manager in RHEL 5.

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