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From: Robert Finch <robfi680@gmail.com>
Newsgroups: comp.arch
Subject: Re: Tonight's tradeoff
Date: Fri, 8 Mar 2024 20:26:08 -0500
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On 2024-03-08 2:41 p.m., George Neuner wrote:
> On Thu, 7 Mar 2024 16:02:45 -0500, Robert Finch <robfi680@gmail.com>
> wrote:
> 
>> A page marked RWE=000 is an unusable page. Perhaps to signal bad memory.
>> Or perhaps as a hidden data page full of comments or remarks. If its not
>> readable-writeable or executable what is it? Nothing should be able to
>> access it, except maybe the machine/debug operating mode.
> 
> The ability to change (at least data) pages between "untouchable" and
> RW is required for MMU assisted incremental GC.  If the GC also
> handles code, then it must be able to mark pages executable as well.
> 
> If an "untouchable" page can't be manipulated by user software, then
> you've disallowed an entire class of GC systems.

Garbage collection seems to be common.

I plan on having garbage collection as part of the OS. There is a shared 
hardware-card table involved. So, I guess that would disallow user 
garbage collectors using untouchable pages. The MMU could be faked out 
using a VM, so I have read.