Sequential Heuristic detection at VFS

["Nirmal Thacker" <thacker.nirmal@xxxxxxxxx>]

Hello,

To be brief the freebsd 5.2 and probably linux as well provides a
generic disk_sort algorithm which sorts the disk requests assuming
elevator scheduling. Although the overhead (and probably necessity) of
this algorithm is minimized since the VFS has some good disk placement
algorithms- now although this is not quite near what I'm trying to do
(the anticipatory disk scheduling), I am curious if such a disk
placement algorithm exist in dragonflybsd.

I did find some kind of sequential heuristics calculation going on at
sys/kern/vfs_vnops.c :

ioflag |= sequential_heuristic(uio,fp);

Although that function(in the same file) is quite confusing. Could
someone tell me what it does there briefly and if there is any kind of
disk placement algorithm at the VFS level too?

Thanks

-nirmal thacker