Re: [U]VM subsystem for L4 X.2 (and later)

[Farid Hajji]

> > needed, because the Hurd (and BSD) heavily rely upon a
> > vm_*() interface and L4's memory management philosophy
> > of recursive pagers is sufficiently different from VM
> > that we need to bridge the gap somehow.
> 
> It is my understanding that the L4 memory management doesn't preclude
> you from using a more traditionaly monolithic VM approach. By "recursive
> pagers", I think you are referring to the notion of spreading the VM
> work out among the threads, to handle requests close to where they came
> from, right? It is a sort of "distributed VM" system.

Yes, that is absolutely correct. We could use a "distributed VM" in the
future, but right now, we need to bootstrap the port somehow. The
easiest (?) way to do it would be to imitate Mach's VM by writing
a 'vmserver' task whose (service)threads can be set as pagers for
regular native L4 threads.

> I don't think anything prevents you from just naming the same thread as
> the pager for all other threads, right?

As far as I understand the X.0 and new X.2 specs, a single thread can
be used for all other threads in the system. I see no problems with
this. The architecture would be:

    Hurd/L4 threads        NetBSD/L4 task
          ^                   ^
          |   .............../
          |  /
          v  v
       vmserver
          ^
          |
          v
        pmap/l4
         ^  ^
        /    \
       v      v
     DMphys  L4 X.2
      on      API
     X.0      on
            X.2/V4

Perhaps, perhaps not.

-Farid.

-- 
Farid Hajji -- Unix Systems and Network Admin | Phone: +49-2131-67-555
Broicherdorfstr. 83, D-41564 Kaarst, Germany  | address@hidden
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