Cache or Direct Access? Revitalizing Cache in Heterogeneous Memory File System

This paper revisits the value of cache in DRAM-PM heterogeneous memory file systems. The first contribution is a comprehensive analysis of the existing file systems on heterogeneous memory, including cache-based and DAX-based (direct access). We find that the DRAM cache still plays an important role in heterogeneous memory. The second contribution is a cache framework for heterogeneous memory, called FLAC. FLAC integrates the cache with the virtual memory management and proposes two technologies of zero-copy caching and parallel-optimized cache management, which deliver the benefits of fast application-storage data transfer and efficient DRAM-PM data synchronization/migration. We further implement a library file system upon FLAC. Microbenchmarks show that FLAC provides a performance increase of up to two orders of magnitude over existing file systems in file read/write. With a real-world application, FLAC achieves up to 77.4% and 89.3% better performance than NOVA and EXT4, respectively.