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1.) All VMs should have a ballon driver installed in them. The hypervisor communicates with the ballon driver to free up and make the memory available to a guest. So in case of
XenSever.
The ballon driver can be found as a part of xen pv or PVHVM drivers. The xen pvhvm drivers are included in upstream linux kernels 2.6.36+.

The DMC (Dynamic Memory Control)capability of the hypervisor should be enabled. only xenserver Advanced and above versions have this feature. In case of xenserver we cannot support an overcommit factor greater than 4. This is because of a hypervisor constraint.

VMware.
In case of VMware the ballon deiver driver can be found as a part of the vmware tools. All the guests that are deployed in a overcommit cluster should have the vmware tools installed.

The memory ballooning is supported by default.

KVM
All the guest are required to support the virtio drivers. All the linux kernels>= 2.6.25 have them installed. Admin needs to activate it. It can be done by setting CONFIG_VIRTIO_BALLOON=y in the virtio configuration.

2.) Hypervisor capabilities.
The hypervisor should be capable of using the memory ballooning. Each of the hypervisor provides their own feature to support ballooning.

xenserver
The DMC (Dynamic Memory Control)capability of the hypervisor should be enabled. only xenserver Advanced and above versions have this feature. In case of xenserver we cannot support an overcommit factor greater than 4. This is because of a hypervisor constraint.

VMware
The memory ballooning is supported by default.

KVM
kvm dose not support automatic adjustment of the guest OS memory dynamically.

Behavior when overcommit is changed while there are VMs running in the cluster.

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As of now cloudstack dose not check for any perquisites. It is the admin's responsibility to provision accordingly.

Things To do

  • Keep these factors in the service offering.
  • Trigger the capacity recalculate when the overcommit is changed. No need to wait until capacity checker runs.
  • Create action event on overcommit change.
  • Create action event when capacity recalculate is complete.