KVA Increase in Different Versions of FreeBSD 4.x

John Kozubik - john@kozubik.com - http://www.kozubik.com

June 23, 2002


Overview


There are very different methods of changing the total amount of
kernel virtual memory (KVM) available in FreeBSD 4.x.  The method change
occurred between 4.4 and 4.5.  This document documents both methods.


(from a June 2002 discussion on freebsd-hackers)


From: John Kozubik (john@kozubik.com)
Subject: Re: (jail) problem and a (possible) solution ? 
Newsgroups: mpc.lists.freebsd.hackers, muc.lists.freebsd.hackers
Date: 2002-06-23 14:57:35 PST 

> > What is the procedure in 4.5-RELEASE (please say "just change
> > KVA_PAGES=260 to KVA_PAGES=512)

(snip)

> For 4.5, you have to hack ldscript.i386 and pmap.h.  I've posted
> on how to do this before (should be in the archives).

Actually, in 4.5 you only need to set:

options KVA_PAGES=512

and recompile your kernel.  It looks like 4.5-RELEASE was the first
release version to _not_ require hacking sys/i386/include/pmap.h and
sys/conf/ldscript.i386.  As you can see by looking at a 4.5-RELEASE 
pmap.h:

#define NKPDE   (KVA_PAGES - 2) /* addressable number of page tables/pde's
*/
#else
#define NKPDE   (KVA_PAGES - 1) /* addressable number of page tables/pde's
*/

the offsets that Terry spoke of are already in place.  This is in contrast
to 4.4-RELEASE:

#define NKPDE                   254     /* addressable number of page
tables/pde's */
#else
#define NKPDE                   255     /* addressable number of page
tables/pde's */

Where everything was hard coded to match the default KVA_PAGES value.  
Further, looking at ldscript.i386 we see in 4.5-RELEASE:

  . = kernbase + 0x00100000 + SIZEOF_HEADERS;

whereas in 4.4-RELEASE and earlier, we saw:

  . = 0xc0100000 + SIZEOF_HEADERS;

Which means that in 4.4 you had to change 0xc0100000 to 0x80100000 for a
2gig KVA.  In 4.5, however, you don't have to change ldscript.i386 at all,
because it is now a relative value that takes kernbase into account.

-----

So, if you are running 4.0 - 4.4, you need to edit ldscript.i386 and
change 0xc0100000 to 0x8010000 (for a 2gig KVA), then you need to edit
pmap.h and change the two lines I pasted above from 254 and 255 to 510 and
511, respectively.

But, if you are running 4.5 or 4.6, from the code I pasted above, it looks
like all you have to do is set:

options KVA_PAGES=512

in your kernel config, then recompile your kernel.

-----

Some background on this concept can be found here:

http://www.kozubik.com/docs/original_kva_increase.txt

I am posting today mainly to get a little more information stored in the
archives.