Linux Device Drivers Development

The Linux page cache – disk caching

The page cache, as its name suggests, is a cache of pages in RAM, containing chunks of recently accessed files. The RAM acts as a cache for pages that resides on the disk. In other words, it is the kernel cache of file contents. Cached data may be regular filesystem files, block device files, or memory-mapped files. Whenever a read() operation is invoked, the kernel first checks whether the data resides in the page cache, and immediately returns it if found. Otherwise, the data will be read from the disk.

If a process needs to write data without any caching involved, it has to use the O_SYNC flag, which guarantees the write() command will not return before all data has been transferred to the disk, or the ...