In message <1086421637.804118.18498.nullmailer@yamt.dyndns.org>YAMAMOTO Takashi
 writes
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>hi,
>
>currently, ext_pgs is merely used as a hint for sodopendfreel().
>i'd like to change it to be used by bus_dmamap_load_mbuf() as well.
>(x86 diff is attached)

Uh, wait a minute: I seem to recall that short-circuiting pa lookups
in bus_dmamap_load_mbuf() was the reason Jason added ext_pgs in the
first place?  Did that last part never quite happen?


>while i think that the change itsself has its own benefits,
>eventual goals are:
>	- delay pmap_kenter_pa() until it's really needed.
>	  (likely on the first mtod()?)
>	  if you're lucky enough, no pmap_kenter_pa() is needed at all.
>	- use mbufs (or something similar) for disk i/o.
>
>comments?

mbufs for disk I/O? You mean something like what OSF1/Digital
Unix/Tru64 called UMC?  "Yes, please". That can help a *lot* for
high-performance NFS, or for sendfile().