Caching or Not: Rethinking Virtual File System for Non-Volatile Main Memory

Virtual File System (VFS) conventionally provides an abstraction for multiple instances of underlying physical file systems as well as metadata caching, concurrency control and permission check, which benefits disk based file systems. However, in this paper we find VFS brings extra overhead when interacting with persistent memory (PM) file systems. We explore the opportunity of shortening VFS stack for PM file systems. We present ByVFS, an optimization of VFS to directly access metadata in PM file systems bypassing VFS caching layer. The results show ByVFS outperforms conventional VFS with cold cache and provides comparable performance against conventional VFS with warm cache. We also present potential issues when reducing VFS overhead.