[syslinux] Large vmalloc segments with PXELINUX

[Mike Polek]

Hello,
  I'm having a challenge with increasing vmalloc memory beyond
512M using pxelinux.0 to boot.

This config works fine:
---
# Configuration file
# linux-2.6.20-1.2962.fc6
DEFAULT linux

LABEL linux
        kernel kernels/vmlinuz-2.6.20-1.2962.fc6
        append initrd=initrds/bladeinitrd-2.6.20-1.2962.fc6.img
enforcing=0 vmalloc=512M
---

  If I increase vmalloc to 513M, I get errors about not being
able to find a root device, root=<NULL> blah blah blah, kind
of like what happens with grub if you don't use "uppermem."
I'm not sure if the command line is getting clobbered, or
if the initrd is loading in the wrong place. Any suggestions
on how to let pxelinux.0 know where to put things when large
amounts of vmalloc memory are required?
  I tried bringing down HIGHMEM_MAX and adjusting the command line
location... and a few other tweaks... but I just don't have the
expertise to figure out exactly where everything is placed.

Thanks!
Mike