Jeff Rizzo wrote:
> In attempting to diagnose why I'm having jumbo-frame problems with a wm
> interface on my G4/466 running -current (~24h old), I tried compiling a
> kernel with "options MCLSHIFT=13", in hopes it would allow me to ping
> across the jumbo-frame link with packets larger than 2002 bytes.
> 
> However, upon booting a kernel which is basically GENERIC with "options
> MCLSHIFT=13", the boot hangs thusly:
> 
> Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
>     The NetBSD Foundation, Inc.  All rights reserved.
> Copyright (c) 1982, 1986, 1989, 1991, 1993
>     The Regents of the University of California.  All rights reserved.
> 
> NetBSD 3.99.11 (GENERIC.MCL) #2: Mon Nov 21 16:44:55 PST 2005
>         riz@grendel:/usr/src/sys/arch/macppc/compile/GENERIC.MCL
> total memory = 1024 MB
> avail memory = 987 MB
> 
> 
> ...then nothing.  A kernel with MCLSHIFT=12 seems to boot and work OK
> (although it doesn't fix my jumbo frame issue - on a link with MTU 4500,
> I still can't get ping packets larger than 2002 bytes across!  "cksum:
> out of data" from every packet)
> 
> So, anyone else see this?  Should I send-pr?  How should I go about
> troubleshooting this, anyway?  :)

Mbufs are pool which means they are not virtually allocated.  Increasing
MCLSHIFT to > 12 means they take multiple pages and the pool allocator
doesn't tolerate that.
-- 
Matt Thomas                     email: matt@3am-software.com
3am Software Foundry              www: http://3am-software.com/bio/matt/
Cupertino, CA              disclaimer: I avow all knowledge of this message.