A memory access profiling and region migration technique makes allocation and replacement decisions for periodic migration of most frequently accessed regions of main memory to least frequently accessed regions of a region migration cache, in background operations. The technique improves performance in sparsely-used memory systems by migrating regions of main memory corresponding to the working footprint of main memory to the region migration cache. A method includes profiling a stream of memory accesses to generate an access frequency ranked list of address ranges of main memory and corresponding access frequencies based on memory addresses in the stream of memory accesses. The method includes periodically migrating to a region migration cache contents of a region of main memory selected based on the access frequency ranked list. The method includes storing a memory address range corresponding to the contents of the region migration cache in a tag map.