A method of managing power in a data processing system includes monitoring a system parameter indicative of power consumption. Responsive to determining that the parameter differs from a specified threshold, a system guest, such as an operating system, is forced to release a portion of its allocated system memory. The portion of system memory released by the guest is then reclaimed by the system. The reclaimed system memory and the resulting decrease in allocated memory may enable the system to reduce system memory power consumption. The operating system may de-allocate a portion of system memory when a balloon code device driver executing under the operating system requests the operating system to allocate memory to it. The system memory allocated to the balloon device driver is then reclaimed by supervisory code such as a hypervisor.