Activity level of memory pages is classified in virtual machine environment, so that processes such as live VM migration and checkpointing, among others, can be carried out more efficiently. The method includes the steps of scanning page table entries of hypervisor-managed page tables continuously over repeating scan periods to determine whether memory pages have been accessed or not, and for each memory page, determining an activity level of the memory page based on whether the memory page has been accessed or not since a prior scan and storing the activity level of the memory page. The activity level of the memory page may be represented by one or more bits of its page table entry and may be classified as having at least two states ranging from hot to cold.