Classification of reads within a filesystem

[Shyam Prasad N <nspmangalore@gmail.com>]

Hi Matthew,

I had a query about a filesystem's ability to differentiate readaheads
from actual reads.
David Howells suggested that you may be able to answer this one. If
not, please feel free to add the right people to this email.

In a scenario where a user/application issues a readahead/fadvise for
large data ranges in advance (informing the kernel that they intend to
read these data ranges soon). Depending on how much data ranges these
calls cover, it could keep the network quite busy for a network
filesystem (or the disk for a block filesystem).

I see some value if filesystems have the ability to differentiate the
reads from regular buffered reads by users. In such cases, the
filesystem can choose to throttle the readahead reads, so that there's
a specified bandwidth that's still available for regular reads.

I wanted to get your opinions about this. And whether this can be done
already in VFS ->readahead and ->readpage calls in the filesystems?

-- 
Regards,
Shyam