A high performance file system for non-volatile main memory

Emerging non-volatile main memories (NVMMs) provide data persistence at the main memory level. To avoid the double-copy overheads among the user buffer, the OS page cache, and the storage layer, state-of-the-art NVMM-aware file systems bypass the OS page cache which directly copy data between the user buffer and the NVMM storage. However, one major drawback of existing NVMM technologies is the slow writes. As a result, such direct access for all file operations can lead to suboptimal system performance. In this paper, we propose HiNFS, a high performance file system for non-volatile main memory. Specifically, HiNFS uses an NVMM-aware Write Buffer policy to buffer the lazy-persistent file writes in DRAM and persists them to NVMM lazily to hide the long write latency of NVMM. However, HiNFS performs direct access to NVMM for eager-persistent file writes, and directly reads file data from both DRAM and NVMM as they have similar read performance, in order to eliminate the double-copy overheads from the critical path. To ensure read consistency, HiNFS uses a combination of the DRAM Block Index and Cacheline Bitmap to track the latest data between DRAM and NVMM. Finally, HiNFS employs a Buffer Benefit Model to identify the eager-persistent file writes before issuing the write operations. Using software NVMM emulators, we evaluate HiNFS's performance with various workloads. Comparing with state-of-the-art NVMM-aware file systems - PMFS and EXT4-DAX, surprisingly, our results show that HiNFS improves the system throughput by up to 184% for filebench microbenchmarks and reduces the execution time by up to 64% for data-intensive traces and macro-benchmarks, demonstrating the benefits of hiding the long write latency of NVMM.