Efficient storage management for aged file systems on persistent memory

Emerging persistent memories (PMs) provide both byte addressability as DRAM and persistency as conventional storage technologies. Recent work on persistent memory file systems, such as BPFS, PMFS, have gained better performance by leveraging the dual characteristics. However, we observe that persistent memory file systems experience dramatic performance degradation over a long run. This phenomenon is referred to as file system aging. We find that the performance degradation is attributed to the inefficiency of storage management for both file space and dentry space. We also find that persistent memories wear out more quickly as file system ages. To address such issues, we propose SanGuo, a novel scatter-gather storage management mechanism for aged file systems on persistent memory. SanGuo consists of two key techniques. First, Scatter-alloc maximizes the efficiency and performance of file allocation while providing wear-leveling. Second, Gather-free accelerates the dentry operations, including dentry allocation, lookup and reclaim, especially for a directory file containing a large number of dentries. Experimental results show that SanGuo performs better wear-leveling while providing significant performance speed up (e.g., up to 10.33×, 8.9× respectively for Webproxy and Varmail workloads).