Building kernels with large MAXDSIZ

[Mike Hunter]

Greetings hackers,

I recently wrote a message to freebsd-questions at freebsd.org about trying
to build a kernel with a large MAXDSIZ for some large network data
crunching I'm trying to do.  I got this reply:

----- Forwarded message from Lowell Gilbert <freebsd-questions-local at be-well.no-ip.com> -----

X-Authentication-Warning: be-well.ilk.org: lowell set sender to freebsd-questions-local at be-well.ilk.org using -f
To: Mike Hunter <mhunter at ack.Berkeley.EDU>
Cc: freebsd-questions at freebsd.org
reply-to: freebsd-questions at freebsd.org
Subject: Re: Can't build kernel with 4GB of memory (MAXDSIZE)
From: Lowell Gilbert <freebsd-questions-local at be-well.no-ip.com>
Date: 22 Aug 2003 11:22:52 -0400
In-Reply-To: <20030820181346.GA21829 at ack.Berkeley.EDU>
User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3

Mike Hunter <mhunter at ack.Berkeley.EDU> writes:

> I can't seem to get a new kernel working with increased memory parameters:
> 
> I tried adding the following to my KERNCONF:
> 
> options         MAXDSIZ="(4096UL*1024*1024)"
> options         DFLDSIZ="(2048UL*1024*1024)"
> 
> On 5-current (as of about 6 months ago) this produced an ungraceful
> init.conf bomb-out.
> 
> I tried again yesterday with a 4.8 box 
> 
> uname -a
> FreeBSD mynewserver.net.berkeley.edu 4.8-RELEASE-p3 FreeBSD
> 4.8-RELEASE-p3 #1: Tue Aug 19 14:24:09 GMT 2003
> root at mynewserver.net.berkeley.edu:/usr/obj/usr/src/sys/raeu  i386
> 
> (cvsup'd some time after August 11)
> 
> It gave me a similar but slightly more graceful bomb-out "I'm not going 
> anywhere without my init!\n\nRebooting in 15 seconds....")
> 
> So, I think I'm missing something here :)  The machine in question has 4GB
> of ram, and I'd like to be able to use all of it for some nasty
> number-crunching I'm trying to do.  Any suggestions?

I'm sorry, but you need to leave some space for the kernel and its
data structures.
I'm not sure how close to the edge you can tune it, but much beyond
3GB or so will probably need some real hacker knowledge...

----- End forwarded message -----

I found this link which helped me understand what I was doing wrong:

http://docs.freebsd.org/cgi/getmsg.cgi?fetch=83003+0+archive/2002/freebsd-hackers/20020804.freebsd-hackers

The question that remains for me is this:  Exactly how big can I set
MAXDSIZ, and how can I influence that maximum?

The machine I'm working with is running 4.8, but I've had the same kinds
of problems on 5-CURRENT as well.

Thanks,

Mike