Ran across this because it's another place where an unsigned long is
passed directly to __pa().  Making the "page" variable a void* seems a
bit more natural than an unsigned long and reduces the net number of
casts by 1.  Without it, we probably need another (void *) cast in the
__pa() call. 

For more explanation as to why this was probably done originally, see
this post:
http://marc.theaimsgroup.com/?l=linux-mm&m=109155379124628&w=2

-- Dave