Write Intensity based Foresightful Page Migration for Hybrid memories

Hybrid main memory combines the benefits of PCM and DRAM while minimizing their respective drawbacks. However, integrating PCM in hybrid memory can be quite difficult due to its shortcomings in write endurance and write latency. Migration of write intensive memory pages across memory units allows improved memory performance by maximizing DRAM capacity and guaranteeing effective use of PCM memory. The two main challenges involved in page migration are choosing which pages to migrate and when to migrate them. Existing page migration techniques move the pages with the highest write counts either immediately when their write count exceeds a threshold or at regular intervals.In this paper, we propose WiMig which migrates pages based on write-intensity. WiMig migrates write intensive pages in regular intervals from a pending queue which keeps track of pages with write count greater than a threshold. We also propose an extension WiForeMig which demotes pages in the pending queue after a specific period. WiForeMig is based on the prediction that pages with lower write intensity and longer in pending queue will get fewer write requests in the future. Thus, WiForeMig reduces unrewarded migrations and improves performance.