Path: utzoo!utgpu!water!watmath!clyde!bellcore!tness7!texbell!killer!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!bu-cs!purdue!decwrl!pyramid!cbmvax!bpa!drexel!jeff
From: jeff@drexel.UUCP (Jeff White)
Newsgroups: comp.sys.next
Subject: Re: Paging and swapping to a removable disk?
Summary: Can you just turn off swapping?
Message-ID: <783@drexel.UUCP>
Date: 21 Oct 88 15:22:29 GMT
References: <12670001@eecs.nwu.edu> <3924@encore.UUCP>
Organization: Drexel University, Phila., Pa.
Lines: 48

In article <3924@encore.UUCP>, bzs@xenna (Barry Shein) writes:
> >Does Mach (on a NeXT, at any rate) do memory swapping to disk?
> >If so, what does it use for the swap area at times when the laser disk is out?
> >(Or are you guaranteed that no page faults or process swapping will occur
> >while you've got nothing in that drive???)
> >
> >Jacob Gore				Gore@EECS.NWU.Edu
> 
> I'll stick my neck out and say that I don't believe that you'll be
> able to remove the optical disk if that's what you're paging and
> swapping to (if you have a winch then it's a whole different matter.)
> 
> I would guess you'd have to bring the system down to a halt to change
> disks. Even if it could stop everything (eg. treat it like Sun does a
> netdisk when a server goes down) what could it do when you pop in a
> different disk? It can't start paging/swapping again, the data on this
> new disk is all wrong, so you'd be hung anyhow, better to reboot.
> 
> Reminiscent of Macs with floppies only where you keep a system folder
> on every application's floppy, only I doubt that's the idea here
> either.
> 
> It would be interesting to hear what, if anything, NeXT has done in
> regards to this. My guess is nothing (ie. to change optical disks you
> bring the system down, change, reboot, unless you have a winch to run
> the system off of, or possibly some sort of NFS protocol to direct all
> swapping/paging to a server.)
> 
> 	-Barry Shein, ||Encore||


  Would it be possible to just turn off the paging/swapping feature?  It would
seem to me that if you have 8 Mbytes of ram in the machine, you should be able
to set up the operating systems to load a program entirely into ram, and then
tell the OS that you have no swap space available.  (What happens on a 
standard 4.2/4.3/Mach system now if you have, say, 8-12 Mbytes of ram, but
only allocate 2 Mbytes or so of swap space to it?).  Unix/Mach is pretty big,
but not that big that you couldn't fit it, along with the one or two programs
you needed when switching optical disks, into 8 Mbytes of ram.  I would think
that you should be able to create a program called 'switch', which would turn
off most of the unnecessary daemons (cron, accounting, tcp connections), copy
the kernal completely into ram, and also copy a small set of programs (stuff
like 'ls' or cp', but probably more advanced) which you would need when swapping
of copying the optical disks.

						Jeff White
						Drexel University - ECE Dept.
						rutgers!bpa!drexel!jeff