Subject: Re: pages.
To: Chris Hopps <>
From: None <>
List: amiga-dev
Date: 03/19/1994 11:47:54
> First let me say that I am working on a newer pmap module to replace
> the current one.  Iwas withlding this information becuase I am not


> Currently we use a page size of 8k.  Almost *all* of the other ports
> use a page size of 4k.  This is a very standard size even outside of
> NetBSD.

4k is the only one supported by the *86 as far as I know, so they didn't
really do a terrific design decision chosing it.. The hp300 port uses 4k
to be compatible to HPUX. SunOS uses 8k pages. There is a big advantage
to 8k pages, too: 8k is one block in a usual ufs/nfs filesystem, improving
hd i/o performance. I worked with Amiga Unix, using 2k pages, and it's i/o
performance *SUCKS*.

> There is also equal or less physical space wasted on adjusting to page
> boundries for all proceses.  (text data bss stack)

I'd rather have a fast system at the cost of slight waste of memory,
than a crawling one using every bit of available memory.

> computers to be Linux, and if we don;t do something about the lack of
> tight resource allocation in NetBSD The amiga community will be
> plagued forever with an SysV type unix.

Come on.. Amiga Unix is pretty dead, NetBSD runs on >= #machines that
were able to run Amiga Unix. I don't consider Linux to be a threat to the
amiga, why shouldn't you let people chose whatever OS they'd like to run?
I certainly don't want to compromise NetBSD by Linux'isms just to get one
or two of potential Linux users 'back' to NetBSD.

> Now back to the pmap, if everything goes well the rewrite I am
> preparing will return basically one *Megabyte* of physical ram
> previously unavailable at boot time.  I am not kidding it was gone and
> never used.  The new pmap will basically provide the same
> functionality using about 30-70k.  I may also attach the 4k page as
> luggage if I am convinced it is the better route.

Interesting! BTW: please, if you're already thinking into pmap internals,
consider how to best support the huge address space open to Zorro3 boards,
too. You'd not want to map this space hardwired like with Z2.. And for 4k:
I think hp300 and even the mac-port are at least considering switching to
8k, please don't stop this process...

> My goal is for AmigaBSD to run on a 2M machine as well as it currently
> runs on  4M machine or better.  With the pmap I will be 3/4's of the
> way there.

Wow.. good luck! That's all I can say.. 

To resume: I think the idea of having NetBSD run on small-memory amigas is
a good idea. As long as this support doesn't compromise performance of amigas
that are better suited to run a unix than any 2M machine could. Don't slow 
16M amigas down, just to also be able to support 2M amigas.

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