Enhancement of cooperation between file systems and applications — on VFS extensions for optimized performance

Abstract

Modern operating systems incorporate an abstract layer called Virtual File System (VFS), which is positioned between user applications and real file systems to hide the differences of various file systems and to expose generic application interfaces for requesting file system services. However, VFS sometimes does not give applications an opportunity to pass information to file systems to help them make correct optimization decisions. In this paper, we review the Linux VFS, discuss its deficiencies and propose several extensions to allow applications to cooperate with the file systems more efficiently. We introduce simple prefetching interfaces and advisory flags to allow applications to communicate application-related semantics to VFS and/or the underlying file systems. These suggestions, which neither affect the semantics of applications nor modify their programming models, not only lead to simple VFS/file systems but also guide them to make correct performance-related decisions, if required. We demonstrate that these interfaces and flags are also easy to implement and can boost application performance by up to 4.29X. Keywords virtual file system, metadata cache, dentry cache, page cache, page readahead CitationWang L, Liao X K, Xue J L, et al. Enhancement of cooperation between file systems and applications -VFS extensions for optimized performance.

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