UMFS: An efficient user-space file system for non-volatile memory

Emerging non-volatile memory (NVM) is expected to be a mainstream storage media in embedded systems for its low-power consumption, near-DRAM speed, high density, and byte-addressability. In-memory file systems are proposed to achieve high-performance file accesses by storing files in NVM. Existing in-memory file systems, such as NOVA and EXT4-DAX, operate in kernel space and have additional overhead caused by kernel layers and mode change. In this paper, we propose a new design of User-space in-Memory File System (UMFS) to improve file access speed by minimizing the overhead of kernel. We implement UMFS in Linux system to verify the proposed design. In open operation, UMFS exposes a file into user-space in constant time independent from the file size. Then, UMFS can achieve high-performance file accesses taking advantages of user virtual address space and existing address translation hardware in processors. We also propose an efficient user-space journaling to ensure data consistency while minimizing kernel cost. Extensive experiments are conducted on standard benchmarks to compare UMFS with NOVA, EXT4-DAX, and SIMFS, the state-of-the-art in-memory file system. The experimental results show that UMFS outperforms any of existing in-memory file systems.