[Xen-users] understanding memory hot-plug in a paravitual domU

[Jordi Moles Blanco <jordi@xxxxxxxxx>]

Hello everyone,

I've been fighting for days with this issue and I would like to ask you 
directly if what i intend to do is actually possible.
let's say I've got a paravirtual domU created with a conf file similar 
to this (this is not a complete one):

***********
kernel='/boot/vmlinuz-2.6.26-2-xen-amd64'
ramdisk='/boot/initrd.img-2.6.26-2-xen-amd64'
memory='2048'
name='server'
vcpus=1
....
extra = "console=tty xencons=tty"
************

so... obviously when i do

********
# xm list
Name                                        ID   Mem VCPUs      State   
Time(s)
Domain-0                                     0  1536     8     r----- 
850454.2
server                                          1  2048     1     -b---- 
1003142.4
*********

i get that 'server' has 2048MB of memory.

Then i start playing with:

**********
# xm mem-max server 4096
# xm mem-max server 4096
**********

and everything seems to work like a charm, none of the above commands 
actually fails or gives any warnings.
but then I do "xm top" or I ssh into 'server' and do "top" and those new 
MB of memory are not present, 'server' hasn't hot-plugged the new memory.
so... is there a way to do that?

i've tried with different domUs (debian, fedora, ...) and also different 
versions of xen: 3.3 i 4.0. The result is always the same, i always need 
to reboot the machine.
I've read all the documentation I've come across and found nothing that 
works.
I've seen some documents with references to acpi hot plug and memory 
hotplug kernel modules, which I've tried to load with no luck. I'm 
successful in loading these modules into the dom0's kernel, but it fails 
in the domU. Actually, the kernel that paravirtual machines use:
/boot/vmlinuz-2.6.26-2-xen-amd64

is compiled with hotplug flags to yes, but it just seems that this is 
not supported in virtualization.
So, i just would like to know if this is possible without rebooting or 
if its a feature in the to-do list.
Thanks in advance.

--
Jordi Moles Blanco
Sistemes Cdmon.com
___________________________
Tlf: 902 36 41 38
Tlf: 93 567 75 77
mailto: jordi@xxxxxxxxx
http://www.cdmon.com


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