From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <7359f049040728082678e0b19c@mail.gmail.com>
Date: Wed, 28 Jul 2004 08:26:42 -0700
From: Rob Pike <robpike@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Subject: Re: [9fans] first casualty of the spam-forced restrictions?
In-Reply-To: <7921dac11109eb57e4975c8c419d7716@terzarima.net>
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i agree. i think the way the MMU is handled in a portable way
is a model of how to do this stuff.  the interface to the rest
of the kernel is only a handful of routines with very specific
properties.  implement them and your system will run.

we've had to adapt the interface a little over time, such as
when page coloring came in for virtual caches, but even
there, the very narrow interface made that easier.

i remember SGI had a 40-page memo on how they implemented
VM on the power series machines.  our MMU trap code was
somewhere close to 40 lines of C.  we weren't quite as
general (there was no way in plan 9 to shrink an address
space), but the lack has never been an issue in practice.
plus, our interface has been ported all over the place; i suspect
IRIX was a little trickier to move to the challenge and then
to the x86 machines.

-rob