在 Linux 的实现中，文件 Cache 分为两个层面，一是 Page Cache ，另一个 Buffer Cache ，每一个 Page Cache 包含若干 Buffer Cache 。内存管理系统和 VFS 只与 Page Cache 交互，内存管理系统负责维护每项 Page Cache 的分配和回收。buffer cache 是块设备的读写缓冲区，更靠近存储设备，或者直接就是disk 的缓冲区。
磁盘操作有逻辑级（文件系统）和物理级（磁盘块），这两种缓存分别是缓存逻辑和物理级数据的。如我们进行的是文件系统操作，那么文件被缓存到Page Cache ，如需要刷新文件的时候，Page Cache 将交给Buffer Cache 去完成，因为Buffer Cache 是缓存磁盘块的。即直接去操作文件就是使用Page Cache ，用dd 等命令直接操作磁盘块，就是buffer cache 缓存。
The Linux Kernel’s VFS Layer
The Virtual File System (VFS) layer  provides a uniform interface for the kernel to deal with various I/O requests and specifies a standard interface that each file system must support. Through this layer, one kernel can mount several different types of file systems (e.g. EXT2FS,ISO9660FS, NFS, …) into the same tree structure. We worked with version 2.2.12 of the Linux kernel and confined our changes to the VFS layer. By doing all of our changes in the VFS layer we kept our predictive prefetching totally independent of the underlying file system.
Arguably, the most important service the VFS layer provides is a uniform I/O data cache. Linux maintains four caches of I/O data: page cache, i-node cache, buffer cache and directory cache. Figure 5 shows these caches and how they interact with the kernel, each other and user level programs. The page cache combines virtual memory and file data. The i-node cache keeps recently accessed file i-nodes. The buffer cache interfaces with block devices, and caches recently used meta-data disk blocks. The Linux kernel reads file data through the buffer cache, but keeps the data in the page cache for reuse on future reads. The directory cache (d-cache) keeps in memory a tree that represents a portion of the file system’s directory structure. This tree maps a file’s path name to an i-node structure and speeds up file path name look up. The basic element of the d-cache is a structure called the d-entry.
We implemented our methods of modeling file access patterns by adding one field to the d-entry structure. The various models would attach their modeling data structure to this pointer. For the last successor model this consisted of just a device and inode number. For the partitioned models this was a pointer to the partition that began with the file that the d-entry identified. After each file access the model would update its predictions. The prefetch engine was then called and would use these predictions to prefetch file data.