Date: Sun, 14 Jan 1996 00:32:07 +1030 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: terry@lambert.org (Terry Lambert) Cc: msmith@atrad.adelaide.edu.au, terry@lambert.org, gibbs@freefall.freebsd.org, phk@critter.tfs.com, jkh@time.cdrom.com, obrien@cs.ucdavis.edu, freebsd-hackers@FreeBSD.org Subject: Re: X for install Message-ID: <199601131402.AAA19555@genesis.atrad.adelaide.edu.au> In-Reply-To: <199601041757.KAA18080@phaeton.artisoft.com> from "Terry Lambert" at Jan 4, 96 10:57:59 am
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(ah, mail backlogs 8)
Terry Lambert stands accused of saying:
> > Why? You load a driver, it sets up whatever it needs in terms of buffers,
> > and then probes. If the probe succeeds, you attach it, if it fails, you
> > throw it all out.
> >
> > The problem with fragmentation is in autodiscard, not autoload.
>
> I agree. How do you fix it?
>
> Typically, I'd say either PIC the code or put drivers in their own
> per driver address space.
... or don't discard, only ever grow. (And obviously have seperate 'probe'
modules. There's only ever one of them around at a time...)
> The "easiest" would be to load them, map them into a "probe space",
> call from "kernel space" to "probe space", and on a hit (where you
> will keep the driver) remap into "kernel space", unmapping from "probe".
Or cons up a 'driver space', load a driver in and let it probe. If it barfs,
throw it out and overwrite it. If it wins, link it in and cons up a new
'driver space'.
> The private address space has the advantage of isolating potentially
> nasty ("scribble on the kernel") drivers, and the disadvantage of
> additional protection domain crossing (ala NetWare 4.x "memory
> protection").
With all the hoohah on pipelining and speculative execution and all that
crap, one never reads much about improvements in these issues (nor TLA and
friends). Is this domain crossing still expensive on newer processors?
(In context, I guess newer means P5+)
> Terry Lambert
--
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