MStream: Stream management for mobile file system using Android file contexts

The Flash-Friendly File System (F2FS) is a widely-used mobile file system. Since it is a log-structured file system (LFS), its segment cleaning operation is a performance bottleneck. To reduce cleaning overhead, F2FS uses the multi-head logging technique, which enables user to write different lifetimes of files into different segments. Currently, F2FS adopts the file-extension-based separation technique. However, it is difficult to predict the lifetime of a file only with the file extension information. In this paper, we analyze the lifetime of each directory of Android mobile application to make a lifetime prediction policy based on directory name and file extension. Each Android application is implemented using a standard Android library and manages files in a similar directory structure. As a result of the analysis, we identified that a single directory contains the file with similar lifetimes. Based on the analysis, we propose a new stream management technique for F2FS, called mStream, which separates the directories with different lifetimes into different segments. At the experiment, mStream reduced the segment cleaning cost by up to 35% compared to the original F2FS.