Management of virtual memory allocated by a virtual machine control program to a plurality of virtual machines. Each of the virtual machines has an allocation of virtual private memory divided into working memory, cache memory and swap memory. The virtual machine control program determines that it needs additional virtual memory allocation, and in response, makes respective requests to the virtual machines to convert some of their respective working memory and/or cache memory to swap memory. At another time, the virtual machine control program determines that it needs less virtual memory allocation, and in response, makes respective requests to the virtual machines to convert some of their respective swap memory to working memory and/or cache memory.