Re: Introducing non-RAM managed page ("device page")

[Masao Uebayashi <uebayasi%tombi.co.jp@localhost>]

> The VM subsystem does not fiddle with the MMU.  pmap does.  The VM 
> subsystem just keeps track of how pages are used.  It's been this way 
> since at least BSD 4.4.

And we don't have API to tell pmap(9) extra information how to map the region.
Device pages are always mapped as non-cached now.  There're cases you want
to map devices with cache enabled, or other configurations like
"write-combining".

I think such configuration informations should be kept in UVM (== struct
vm_page *), other than calling cdev_mmap() each time when it's mapped.  By
making device pages as struct vm_page * and teach the generic uvm_fault()
how to handle them, udv_fault() can go away in the long-run.

Masao