Subject: Re: port-i386/1909: NKPDE fix.
To: John Dyson <dyson@freefall.freebsd.org>
From: Neil J. McRae <neil@revelation.domino.org>
List: netbsd-bugs
Date: 01/08/1996 10:05:11
> >
> > This has the unfortunate side effect that it wastes something like
> > 19 * 4K of wired memory... 76K is a lot of wired memory to throw away
> > on a 4M machine.
> >
> > a better way to do it would be to make kernel page table space
> > dynamically allocated... but that's harder. 8-)
> >
Our machine has 128M of ram :-)
> FreeBSD allocates virtual space for 256MB of kernel, but starts with only 9
> kernel page table pages. It grows dynamically as needed, up to 63 kernel pag e
> table pages. Of course it is done in a machine independent fashion in
> the upper layers (and calls an optional pmap routine for low level support.)
> Architectures that don't need that support don't need to do anything in
> the special pmap routine. We have had that support for 1yr now. There
> were two reasons for the support -- one eliminating another error prone
> tunable, and secondly at one time I was going to fault I/O into the
> kernel space (more kva needed) -- but that was very inefficient, so decided
> not to do it.
>
Thanks John. So who fancies putting this into NetBSD ? :-)
Regards,
Neil.
--
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