1. A non-transitory machine-readable medium having executable instructions to cause one or more processing units to perform a method to track virtual memory access by a graphics processing unit of a device, the method comprising: detecting an access to a virtual memory address by a processing unit, wherein the device includes a central processing unit and the graphics processing unit that are each able to access the virtual memory address; determining if the processing unit is a graphic processing unit; and if the processing unit is the graphics processing unit, setting a graphics processing unit reference bit in a page table entry of a page table that corresponds to the virtual memory address, wherein the page table is shared between the central processing unit and the graphic processing unit.