Management of Virtual Memory Systems under High Performance PCM-based Swap Devices

As high performance NVM storage such as PCM or STT-RAM emerges, legacy software layers optimized for HDDs should be revisited. This paper explores the performance of a system that uses PCM as the swap device of virtual memory and discusses how this system can be managed efficiently. Specifically, we explore the challenges and implications of using PCM swap devices with a broad range of experiments in comparison with traditional HDD swap devices. For PCM swap devices, we evaluate the performance by attaching PCM on DIMM slots, thereby eliminating the software stack overhead of block I/O and the context switch time. To assess the potential benefit of PCM swap devices, we change various configurations and perform experiments to quantify the effects of memory management mechanisms and parameters such as page size, read-ahead options, page replacement algorithms, and total memory capacity. The results show that reducing the page size and turning off the read-ahead option improve the performance of PCM-based swap systems where the page fault handling time is sufficiently small. We also show that the performance is not degraded even with a small DRAM memory under a PCM swap device, this leads to the reduction of DRAM's energy consumption significantly compared to HDD-based swap systems. We anticipate that our results will provide directions in system software development in presence of ever faster swap devices.