kiobuf interface / PG_locked flag

[Martin Maletinsky <maletinsky@scs.ch>]

Hello,

I just read about the kiobuf interface in the Linux Device Driver book from Rubini/Corbet, and there is one point, which I don't understand:
- map_user_kiobuf() forces the pages within a user space address range into physical memory, and increments their usage count, which subsequently prevents the pages from
being swapped out.
- lock_kiovec() sets the PG_locked flag for the pages in the kiobufs of a kiovec. The PG_locked flag prevents the pages from being swapped out, which is however already
ensured by map_user_kiobuf().
(1) What is the reason to call lock_kiovec()?
(2) Are there any additional effects (other than prevent the page from being swapped out) resulting from a set PG_locked flag?
(3) Does anyone know a more detailed documentation of the kiobuf interface, than the book mentioned above?

P.S. please put me on CC in your reply, since I am not in the mailing list.

Thanks for any help,
best regards
Martin Maletinsky

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Supercomputing System AG          email: maletinsky@scs.ch
Martin Maletinsky                 phone: +41 (0)1 445 16 05
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CH-8005 Zurich


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