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

From: Ian Duggan
Subject: Re: [U]VM subsystem for L4 X.2 (and later)
Date: Wed, 13 Mar 2002 13:30:03 -0800

> 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 think the first goal should be to just get something that works
implemented. We could refine things after that. You mentioned before
that the OSKIT had a lib that utilized the UVM. The first step should be
to create a memserver that uses the simple VM in OSKIT, or if the author
is ambitious, jump right to the OSKIT UVM. That would allow us to better
understand what the mem server's interfaces need to look like. It would
allow us to do some prototyping before building the real UVM memserver.

> 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.

Nice art. I just wonder how the heuristics in the VM will be affected
when it has two different OSes driving it rather than one. It will be
interesting to see.

Like I said, I think we should focus on building the simple thing first,
and then work on refining it. I'm putting my effort into getting a set
of device drivers working for the system, looking at the DDE stuff and
possibly OSKIT as a first step. If someone else wanted to work on the
memserver that would be great. If no one has picked it up when I finish
the driver stuff, then I'll take a whack at it. It's just always nice to
parallelize effort.

-- Ian

Ian Duggan                    address@hidden

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