HTMFS: Strong Consistency Comes for Free with Hardware Transactional Memory in Persistent Memory File Systems

File system designs are usually a trade-off between performance and consistency. A common practice is to sacrifice data consistency for better performance, as if high performance and strong consistency cannot be achieved simultaneously. In this paper, we revisit the trade-off and propose HOP, a lightweight hardware-software cooperative mechanism, to present the feasibility of leveraging hardware transactional memory (HTM) to achieve both high performance and strong consistency in persistent memory (PM) file systems. The key idea of HOP is to pick the updates visible to the file system interface and warp them into HTM. HOP adopts an FS-aware Optimistic Concurrency Control (OCC)-like mechanism to overcome the HTM capacity limitation and utilizes cooperative locks as fallbacks to guarantee progress. We apply HOP to build HTMFS, a user-space PM file system with strong consistency. In the evaluation, HTMFS presents up to 8.4× performance improvement compared to state-of-the-art PM file systems, showing that strong consistency can be achieved in high-performance persistent memory.