Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!nuchat!sugar!peter
From: peter@sugar.UUCP (Peter da Silva)
Newsgroups: comp.sys.amiga
Subject: Re: The Next Generation
Message-ID: <1099@sugar.UUCP>
Date: Sun, 22-Nov-87 10:21:50 EST
Article-I.D.: sugar.1099
Posted: Sun Nov 22 10:21:50 1987
Date-Received: Wed, 25-Nov-87 02:57:27 EST
References: <2785@megaron.arizona.edu> <17218@glacier.STANFORD.EDU> <360@usl-pc.UUCP>
Organization: Sugar Land UNIX - Houston, TX
Lines: 46
Summary: Swapping vs. Paging

In article <360@usl-pc.UUCP>, jpdres10@usl-pc.UUCP (Green Eric Lee) writes:
> In message <17218@glacier.STANFORD.EDU>, jbn@glacier.STANFORD.EDU (John B. Nagle) says:
> >    1.  Given the way that RAM prices are declining while
> >	disk access times are not improving, virtual memory
> >	looks like an idea whose time has passed.  
> Only if you have a single-tasking operating system. Certainly you can
> get enough physical memory nowadays to run ANY respectable program.
> But what if you have FIFTEEN 2 megabyte programs loaded up?...

Swap them.

I know swapping is not as chic as paging, but it should be possible.

It requires fewer smarts on the part of the operating system, because the
working set for any program is either in or out of memory. It also doesn't
incur the overhead of page faulting. On the other hand, it does require a lot
more I/O per swap.

Here's my fantasy for the Amiga:

68020 with MMU. NO VM.

Task address space:

	0-1M		Chip memory, shared and private.
	1M-16M		I/O and Shared fast memory.
	16M+		Mapped (managed) private memory.

Not all of 0-16M is addressible by every task, of course. Just stuff that's
MEMF_PUBLIC.

The stuff in private memory can be swapped out. The program won't know or
care if it's in a different place in real memory when it gets back. Give
it a signal (SIGB_SWAPPED) when it gets back in, so it can handle any cleanup.

Of course this may all be really running in whatever memory you have, both
inside and outside 16M.

Add another Alloc bit. MEMF_SYSTEM. Like MEMF_PUBLIC but not shared by other
tasks unless they've got the system flag set in their TCB.

This should be completely compatible with existing software, so long as it has
been scrupulous about MEMF_PUBLIC.
-- 
-- Peter da Silva  `-_-'  ...!hoptoad!academ!uhnix1!sugar!peter
-- Disclaimer: These U aren't mere opinions... these are *values*.