Exploiting phase-change technology in server memory systems

Abstract

OF THE DISSERTATION Exploiting Phase-Change Technology in Server Memory Systems by Luiz Eduardo da Silva Ramos Dissertation Director: Ricardo Bianchini Main memory capacity is becoming a critical issue for modern server systems. Unfortunately, current trends suggest that meeting these capacity requirements using DRAM will not be ideal. DRAM consumes significant amounts of energy (idle, refresh, and precharge energies) and will soon reach its density limit. Many researchers in industry and academia point to Phase-Change Memory (PCM) technology as a promising replacement for DRAM. PCM is byte-addressable as DRAM, but presents higher density and lower idle power consumption than DRAM. However, PCM is also slower than DRAM and has limited endurance. For these reasons, hybrid memory systems that combine a small amount of DRAM and a large amount of PCM have become attractive. In this dissertation, we propose two hybrid memory systems for servers. The first system (called Rank-aware Page Placement or RaPP) is a hardware-driven page placement policy. The policy relies on the memory controller (MC) to monitor access patterns, migrate pages between DRAM and PCM, and translate the memory addresses coming from the cores. The second system (called Rank-aware Cooperative Cache or RaCC) is a software-driven policy for object placement in server clusters that implement cooperative memory caches. RaCC monitors object popularity and leverages that