FlatFS: Flatten Hierarchical File System Namespace on Non-volatile Memories

The conventional file system provides a hierarchical namespace by structuring it as a directory tree. Tree-based namespace structure leads to inefficient file path walk and expensive namespace tree traversal, underutilizing ultra-low access latency and good sequential performance provided by non-volatile memory systems. This paper proposes FlatFS, a NVM file system that features a flat namespace architecture while provides a compatible hierarchical namespace view. FlatFS incorporates three novel techniques: coordinated file path walk model, range-optimized NVM-friendly B^{r} tree, and write-optimized compressed index key layout, to fully exploit flat namespace structure to improve file system namespace performance on high-performance NVMs. Evaluation results demonstrate that FlatFS achieves significant performance improvements for metadata-intensive benchmarks and real-world applications compared to other file systems.