CentOS virt - Jun 2011 - More than 32G on memory in a domU guest?

I must be missing something obvious. I have a large domU guest:

dom0# cat /etc/xen/turing 
name = "turing"
uuid = "8d3383a0-f0ae-f0b1-215d-c2e04115e9fe"
maxmem = 40000
memory = 40000
vcpus = 12
bootloader = "/usr/bin/pygrub"
kernel = "/var/lib/xen/boot_kernel.nrTJko"
ramdisk = "/var/lib/xen/boot_ramdisk.y6Gcn9"
extra = "ro root=/dev/mapper/SYSTEM-root SYSFONT=latarcyrheb-sun16
LANG=en_AU.UTF-8 KEYTABLE=us console=hvc0 earlyprintk=xen"
on_poweroff = "destroy"
on_reboot = "restart"
on_crash = "restart"
vfb = [ "type=vnc,vncunused=1,keymap=en-us" ]
disk = [ "phy:/dev/VM/system,xvda,w",
"phy:/dev/VM/home,xvdb,w" ]
vif = [
"mac=00:16:3e:7d:d0:91,bridge=xenbr0,script=vif-bridge,vifname=vif3.0"
]

dom0# xm list
Name                                      ID Mem(MiB) VCPUs State Time(s)
Domain-0                                   0     3907    16 r----- 66831.9
turing                                     1    40000    12 r----- 1842736.7

So it looks like I should have 40G of memory available to my guest. The
guest boots like this (from /etc/grub.conf of guest):

title Fedora (2.6.35.13-92.fc14.x86_64)
	root (hd0,0)
	kernel /vmlinuz-2.6.35.13-92.fc14.x86_64 ro root=/dev/mapper/SYSTEM-root
SYSFONT=latarcyrheb-sun16 LANG=en_AU.UTF-8 KEYTABLE=us console=hvc0
earlyprintk=xen
	initrd /initramfs-2.6.35.13-92.fc14.x86_64.img

However, the guest reports this:

domU# grep MemTotal /proc/meminfo 
MemTotal:       32870604 kB

What did I miss?


Additional info:

dom0# xm info
host                   : neumann.une.edu.au
release                : 2.6.18-238.12.1.el5xen
version                : #1 SMP Tue May 31 14:02:29 EDT 2011
machine                : x86_64
nr_cpus                : 16
nr_nodes               : 1
sockets_per_node       : 4
cores_per_socket       : 4
threads_per_core       : 1
cpu_mhz                : 2132
hw_caps                :
bfebfbff:20100800:00000000:00000940:000ce33d:00000000:00000001
total_memory           : 65534
free_memory            : 20354
node_to_cpu            : node0:0-15
xen_major              : 3
xen_minor              : 1
xen_extra              : .2-238.12.1.el5
xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32
hvm-3.0-x86_32p hvm-3.0-x86_64
xen_pagesize           : 4096
platform_params        : virt_start=0xffff800000000000
xen_changeset          : unavailable
cc_compiler            : gcc version 4.1.2 20080704 (Red Hat 4.1.2-50)
cc_compile_by          : mockbuild
cc_compile_domain      : centos.org
cc_compile_date        : Tue May 31 13:13:40 EDT 2011
xend_config_format     : 2


-- 
Norman Gaywood, Computer Systems Officer
University of New England, Armidale, NSW 2351, Australia

ngaywood at une.edu.au            Phone: +61 (0)2 6773 3337
http://mcs.une.edu.au/~norm    Fax:   +61 (0)2 6773 3312

Please avoid sending me Word or PowerPoint attachments.
See http://www.gnu.org/philosophy/no-word-attachments.html

Hmm bad form to answer myself, but:

On Wed, Jun 29, 2011 at 09:41:18AM +1000, Norman Gaywood
wrote:
> dom0# cat /etc/xen/turing 
...
> maxmem = 40000
> memory = 40000
 
> dom0# xm list
...
> turing                                     1    40000    12 r-----
1842736.7
> guest boots like this (from /etc/grub.conf of guest):
> title Fedora (2.6.35.13-92.fc14.x86_64)
 
> However, the guest reports this:
> 
> domU# grep MemTotal /proc/meminfo 
> MemTotal:       32870604 kB
I missed this in /usr/src/kernels/2.6.35.13-92.fc14.x86_64/.config

CONFIG_PARAVIRT_GUEST=y
CONFIG_XEN=y
CONFIG_XEN_MAX_DOMAIN_MEMORY=32

So I guess that means that the fedora kernels are not built to use more
than 32G of memory in DomU.

-- 
Norman Gaywood, Computer Systems Officer
University of New England, Armidale, NSW 2351, Australia

ngaywood at une.edu.au            Phone: +61 (0)2 6773 3337
http://mcs.une.edu.au/~norm    Fax:   +61 (0)2 6773 3312

Please avoid sending me Word or PowerPoint attachments.
See http://www.gnu.org/philosophy/no-word-attachments.html