Starting with VirtualBox 4.0.8 a new host executable called
VBoxBalloonCtrl is available to
automatically take care of a VM's configured memory balloon
(see Section 4.8.1, “Memory ballooning” for an introduction to memory
ballooning). This is especially useful for server environments where
VMs may dynamically require more or less memory during runtime.
VBoxBalloonCtrl periodically checks a VM's current memory balloon and its free guest RAM and automatically adjusts the current memory balloon by inflating or deflating it accordingly. This handling only applies to running VMs having recent Guest Additions installed.
To set up VBoxBalloonCtrl and adjust the maximum ballooning size a VM can reach the following parameters will be checked in the following order:
--balloon-maxVBoxManage setextradata "VM-Name" VBoxInternal/Guest/BalloonSizeMax <Size in MB>
VBoxManage setextradata global VBoxInternal/Guest/BalloonSizeMax <Size in MB>
If no maximum ballooning size is specified by at least one of the parameters above, no ballooning will be performed at all.
For more options and parameters check the built-in command line help
accessible with --help.