Subject: Re: port-i386/1909: NKPDE fix.
To: John Dyson <>
From: Neil J. McRae <>
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 ? :-)

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