Selective main memory compression by identifying program phase changes

We present a new approach to main memory compression in which a mostly software solution is suggested but without the processing power penalty that usually accompanies such a solution. Compression is only performed during phases which exhibit good spatial locality. These phases are identified by detecting changes in the program's working set. By comparing the current working set's "signature" with the signature at the end of the previous instruction window, a difference parameter is calculated and, when the difference is low enough, the program is in a phase that exhibits good locality and thus compression may begin. Simulation results confirm that this new approach to main memory compression provides good compression ratios for most SPEC CPU2000 programs.