Path: utzoo!attcan!uunet!cs.utexas.edu!sun-barr!ames!pasteur!agate!web-1g.berkeley.edu!c60c-1ea
From: c60c-1ea@web-1g.berkeley.edu (Yen Yuanchi Hsieh)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Virtual Memory
Message-ID: <24384@agate.BERKELEY.EDU>
Date: 12 May 89 21:40:25 GMT
References: <9140@polya.Stanford.EDU>
Sender: usenet@agate.BERKELEY.EDU
Organization: University of California, Berkeley
Lines: 39

In article <9140@polya.Stanford.EDU> rokicki@polya.Stanford.EDU (Tomas G. Rokicki) writes:
>It would be intensely neat if someone would demonstrate an Amiga with
>2620 running VM during the next DevCon.  (Too bad I don't have a 2620
>to play with.)  Perhaps we can discuss any complications that might
>arise?

Well, I won't be at DevCon -- so let's talk about some right now [which you
go ahead and do anyway...]

>Page faulting during Forbid()/Permit() might be acceptable, if the
>page fault handler doesn't modify any standard system structures, just
>the VM state stuff, which sounds reasonable.  Disable()/Enable() may
>or may not be something else again.

Actually, I was thinking that one might be able to do Forbid()s merely by
write-protecting the page-to-be-loaded.
Then when a 'non-owner-of-this-page' occurs, have the interrupt handler
check if the owner-of-this-page has Forbid()den, restart that task if it has
(default error if it hasn't) and clear the write-protect on the page.

Disable()s would need to be changed into Forbid()s, of course...

It's not the best approach.  If you Forbid on Exec structures -- exec
structures that need to be read by Exec Switch(), that might cause
problems.  Any way to run Exec SU and avoid that situation?  Also, you need
to be careful coming out of all of this.  I mean, someone could have Forbid(),
mistakenly Wait()ed, and then have one of his pages readable that shouldn't
have been.  But this seems more reasonable if it's doable...

>You know, folks, this could really be wonderful.

I hope so...

>-tom

-----------------------------------------------
David Navas   c60c-1ea@WEB.Berkeley.Edu
Ideas?  What ideas?  If I had any idea I'd have
an idea, I wouldn't have posted this nonsense.