RMMIO: Enabling Reliable Memory-Mapped I/O for Persistent Memory Systems

The byte-addressable persistent memory (PM) is coming to be the next-generation storage device for better I/O performance. As the traditional I/O path is too lengthy to drive PM featuring low latency and high bandwidth, prior works have proposed memory-mapped I/O (MMIO) to shorten the I/O path to PM. However, native MMIO directly maps files into the user address space, which puts files at risk of user-space scribbles and non-atomic I/O interfaces, termed reliability issues. Since existing reliability schemes cause significant extra overheads, we propose RMMIO, an efficient user-space library that provides reliable memory-mapped I/O interfaces for PM systems. RMMIO achieves a good balance between efficiency and reliability by introducing a memory-mapped cache layer upon kernel file systems. The cache layer accelerates I/O requests and carries the file system's responsibility for data reliability by data isolation. In addition, RMMIO further employs lightweight snapshots and efficient atomic I/O interfaces to guarantee the integrity and consistency of the data in the cache layer at low costs. The experimental results show that RMMIO achieves 8.49x higher throughput than ext4-DAX and 2.31x higher throughput than state-of-the-art MMIO-based schemes for PM while ensuring data reliability.