TempFFS: Enabling Delayed Allocation for Existing File Systems

Abstract

Based on the previous observation that many files are short-lived, some advanced file systems delay the block allocation of their files until the file data needs to be written back to disk. Such delayed allocation feature can reduce the IO traffic as well as the degree of file fragmentation, and thus results a better IO performance. However, a file system can enjoy the benefit of delayed allocation only when it explicitly implements the feature. In this paper, we design and implement a temporary-file file system called TempFFS to allow all the existing file systems to enjoy the benefit of delayed allocation. Based on the concept of stackable file system, TempFFS places all newly-created files in memory and transfers these files to their original file systems as needed. We implement TempFFS in the Linux kernel. Performance results show that, with the help of TempFFS, both the disk IO traffic and the degree of file fragmentation can be largely reduced, resulting a performance improvement of 34% to 69% under a file system benchmark, Postmark.