A method and a computer system for memory management on a virtual machine system are provided. The memory management method includes the following steps. A least recently used (LRU) list is maintained by at least one processor according to a last access time, wherein the LRU list includes a plurality of memory pages. A first portion of the memory pages are stored in a virtual memory, a second portion of the memory pages are stored in a zram driver, and a third portion of the memory pages are stored in at least one swap disk. A space in the zram driver is set by the at least one processor. The space in the zram driver is adjusted by the processor according to a plurality of access probabilities of the memory pages in the zram driver, an overhead of a pseudo page fault, and an overhead of a true page fault.