Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!bbn.com!rsalz
From: rsalz@bbn.com (Rich Salz)
Newsgroups: comp.unix.wizards
Subject: How to write a new Unix-like kernel
Message-ID: <2046@prune.bbn.com>
Date: 20 Oct 89 15:04:14 GMT
References: <17166@rpp386.cactus.org> <1989Oct19.220105.10185@ico.isc.com>
Organization: BBN Systems and Technologies Corporation
Lines: 31

In <17166@rpp386.cactus.org> jfh@rpp386.cactus.org (John F. Haugh II) writes:
> ... discouraging paging
> the kernel is kinda wasteful the way kernels keep bloating.

Take this sentence backwards, and it becomes a feature:  since the kernel
can't page, you can't puff lots of stuff into it.  This has forced a
certain economy of design (phrase lifted from one of the Unix papers, read
them all and find out which one -- it'll be good for you) that has
resulted in the initial success of Unix lo these many years ago.

I don't think this bloat is necessary, and as Dick Dunn has implied in
<1989Oct19.220105.10185@ico.isc.com>, if you make it possible to have the
kernel page, then all you do is make it possible to have every
semi-competent bozo put everything they want in the kernel.  Goodbye
tasteful and understandable set of features, hello [VM][MV]S.

On the other hand, if you let the kernel page, then you can take all the
stuff that doesn't page and call that the "real" kernel.  As long as it's
paging the other parts, put them in user space, and give users the
opportunity to put their own code in for their programs.

I don't expect someone whose .signature says that Mach stands for
messages are crufty hacks will like this design very much, but I'd
rather avoid bloat, myself.  (Do I have to say that this is intended
to be a mild tweak and not one of the famous "Usenet ad hom.
attacks"?)

	/r$
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