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From: mcm@redwood.ucsb.edu (Marcelo C. Mourier)
Newsgroups: comp.os.minix
Subject: Re: 386 Memory Management
Message-ID: <5602@hub.ucsb.edu>
Date: 1 Jun 90 17:48:02 GMT
References: <611@philica.ica.philips.nl>
Sender: news@hub.ucsb.edu
Reply-To: mcm@redwood.UUCP (Marcelo C. Mourier)
Organization: University of California, Santa Barbara
Lines: 33

In article <611@philica.ica.philips.nl> adrie@.ica.philips.nl () writes:
>
>The best method would be to change the MM to divide the physical memory
>in pages of 4KBytes (most paging MMU's, including the SparcStation's MMU
>and the I386, use 4K pages), and deliver physical memory to the processes
>as they need it.
>
>So how did the 386-guys implement it? Do they use paging and/or
>segmenting? Is Andy willing to change the MM to adapt to paging MMU's?
>
>Adrie Koolen,
>Philips Innovation Centre Aachen, (West-)Germany
>e-mail: adrie@ica.philips.nl

I'm working on a 32-bit kernel for Minix on the i386 that's going to use the
paging mechanism of the CPU to implement virtual memory.  As a consequence I
made some substantial changes to the way the virtual address space of a pro-
cess is laid out, and the way memory management is done.  Actually, I'm con-
sidering moving all the MM code to the system task in the kernel, instead of
having it as a separate server process.  This way, a lot of overhead would
be eliminated between the kernel and the MM process, which is necessary be-
cause now we have to deal with page-faults!

The approach I'm taking completely skips the segmentation mechanism of the 
i386, all segments are based at linear address zero, and are 4G-long.  This
way the virtual address space == linear address space, and all the remaping
is done by the paging mechanism.

I'm using SCO's Unix V/386 as the developement system and I still have a long
way to go.  I'm using Minix 1.5 as a reference.  If there's anyone interested
I could periodically post or mail the progress/retrocess I make...

Marcelo - mcm@cs.ucsb.edu