操作系统原理11章节(1325KB).ppt

Grouping The first free block contains the addresses of n other free blocks. For each group, the first n-1 blocks are actually free and the last (i.e., n-th) block contains the addresses of the next group. In this way, we can quickly locate free blocks. Operating System Concepts Address counting We can make the list short with the following trick: Blocks are often allocated and freed in groups We can store the address of the first free block and the number of the following n free blocks. Operating System Concepts Efficiency and Performance Efficiency dependent on: disk allocation and directory algorithms types of data kept in file’s directory entry Performance disk cache – separate section of main memory for frequently used blocks free-behind and read-ahead – techniques to optimize sequential access improve PC performance by dedicating section of memory as virtual disk, or RAM disk Operating System Concepts Page Cache A page cache caches pages rather than disk blocks using virtual memory techniques Memory-mapped I/O uses a page cache Routine I/O through the file system uses the buffer (disk) cache This leads to the following figure Operating System Concepts I/O Without a Unified Buffer Cache Operating System Concepts Unified Buffer Cache A unified buffer cache uses the same page cache to cache both memory-mapped pages and ordinary file system I/O Operating System Concepts I/O Using a Unified Buffer Cache Operating System Concepts Chapter 11: File System Implementation 张竞慧 jhzhang@seu.edu.cn Chapter 11: File System Implementation File System Structure File System Implementation Directory Implementation Allocation Methods Free-Space Management Efficiency and Performance Recovery Log-Structured File Systems NFS Operating System Concepts File-System Structure File structure Logical storage unit Collection of related information File system resides on secondary storage (disks). File system organized into layers. File control block – storage structur