A DAX-enabled mmap mechanism for log-structured in-memory file systems
Zhixiang Mao, Shengan Zheng, Linpeng Huang, Yanyan Shen · 2017
Emerging byte-addressable Non-Volatile Memory(NVM) technologies offer fine-grained access to persistent data with latency comparable to DRAM. This presents both challenges and opportunities to system software designers. To utilize the fascinating features of NVM, a lot of works have been done to develop NVM-based file systems. Direct access (DAX) is a key feature provided by most NVM-based file systems, it enables applications to directly access NVM without going through the page cache layer. However, DAX-style mmap may cause serious consistency issues in versioning in-memory file systems that adopt CoW to solve block sharing problem among snapshots. In this paper, we propose a new mmap mechanism called versioning-mmap which solves the consistency issue of memory-mapped I/O in DAX-enabled versioning in-memory file systems. We implement our proposed mechanism in HMVFS and do a series of experiments based on our implementation. Results show that our mechanism achieves consistency while imposing negligible performance overhead compared to PMFS and NOVA.