The lookup procedure in Linux costs a significant portion of file accessing time as the virtual file system (VFS) traverses the file path components one after another. The lookup procedure becomes more time consuming when applications frequently access files, especially those with small sizes. We propose Stage Lookup, which dynamically caches popular directories to speed up lookup procedures and further reduce file accessing latency. The core of Stage Lookup is to cache popular dentries as shortcuts, so that path walks do not bother to traverse directory trees from the root. Furthermore, Stage Lookup enriches backward path walks as it treats the directory tree in a VFS as an undirected map. We implement a Stage Lookup prototype and integrate it into Linux Kernel v3.14. Our extensive performance evaluation studies show that Stage Lookup offers up to 46.9% performance gain compared to ordinary path lookup schemes. Furthermore, Stage Lookup shows smaller performance overheads in rename and chmod operations compared to the original method of the kernel.

中文翻译：

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阶段查找：使用目录快捷方式加速路径查找

由于虚拟文件系统 (VFS) 一个接一个地遍历文件路径组件，因此 Linux 中的查找过程花费了大量的文件访问时间。当应用程序频繁访问文件时，查找过程会变得更加耗时，尤其是那些小文件。我们提出了 Stage Lookup，它动态缓存流行目录以加快查找过程并进一步减少文件访问延迟。Stage Lookup 的核心是将流行的 dentry 缓存为快捷方式，这样路径遍历就不必费心从根遍历目录树。此外，Stage Lookup 丰富了反向路径遍历，因为它将 VFS 中的目录树视为无向映射。我们实现了 Stage Lookup 原型并将其集成到 Linux Kernel v3.14 中。我们广泛的性能评估研究表明，与普通路径查找方案相比，Stage Lookup 可提供高达 46.9% 的性能增益。此外，与内核的原始方法相比，Stage Lookup 在重命名和 chmod 操作中显示出更小的性能开销。