问题
May i know in linux kernel what is the difference between filesystem I/O (GFP_FS) and Disk I/O (GFP_IO)?
回答1:
It is plain and simple that filesystem I/O is I/O happening on the filesystem. Lets say you are reading/writing on a file which is represented on the filesystem. The disk IO is the IO happening directly on the disk. This is block IO. On a layering standpoint you can say, the disk IO happens at a low level than the file system IO. And you can even say, the filesystem IO may get translated to disk IO.
It may also worth notable that the filesystem io may happen without an associated disk IO on cached data/files or for a filesystem which is not backed up by a disk. Say, a ramdisk filesystem, ofcourse the /proc/ filesystem.
来源：https://stackoverflow.com/questions/19496292/difference-b-w-filesystem-i-o-gfp-fs-and-disk-i-o-gfp-io