Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MMU + A3000 + AmigaOS2.0 == Non-crashing system?
Message-ID: <13655@cbmvax.commodore.com>
Date: 6 Aug 90 20:20:07 GMT
References: <2489@clinet.FI> <13624@cbmvax.commodore.com> <1990Aug6.115552.14352@sisd.kodak.com>
Reply-To: jesup@cbmvax (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 26

In article <1990Aug6.115552.14352@sisd.kodak.com> jeh@athena.sisd.kodak.com (Ed Hanway) writes:
>valentin@cbmvax (Valentin Pepelea) writes:
>>Backward compatibility.
>
>As an intermediate step to full memory protection, why not just forbid read
>and write access to free memory?  This won't do a thing to stop programs
>from corrupting each other, but it might help catch the bugs that cause
>these problems.  I think the only "correct" programs that might break
>under this scheme would be those that use the kind of non-standard memory
>allocation like VD0:.

	However, the granularity has to be increased to 256 bytes (smallest
page size in the MMU), and you need _big_ page tables, and the overhead of
AllocMem/FreeMem gets much larger.  Probably not something I'd want for
a production user environment for the moment.

	Other things break: anything that frees part of an allocation.  This
is at best only quasi-legal, though layers currently does it with cliprects
to reduce overhead/fragging.

	Good debugging tool, though.  Fix the programs and all users benefit.

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.cbm.commodore.com  BIX: rjesup  
Common phrase heard at Amiga Devcon '89: "It's in there!"