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.