Is there a reason (besides conservatism) that this
   is done on a whole-uio base?
   The uio is unrolled in fs code later anyway, and having
   the hook there (or even integrating it into ubc_alloc???)
   would allow for more fine-grained alignment checks,
   eventually loaning single pages out of a smaller read().
   
   Didn't look deeper, just trying to understand...


i'm not sure this is relevant or not but page loaning is not
efficient for less than page sized items...


.mrg.