CentOS virt - Feb 2008 - Issue with dom0 xen ballooning

Hi all,
I'm having issue with my Centos 5.1 /Xen installation.
I'm having  some  dom0 running 2.6.18-53.1.6.el5xen (x86_64).
On the dom0 where the load is high (more than 70% of total system memory 
consumed by dom0 and domU) we have a  lot of  "memory squeeze ".
The result is that the domU seems to be blocked (no network/no disk 
acces/ etc....).

Looking for a solution in xen user list, it seems the problem come from 
dom0 xen ballooning.
With this option the dom0 attempt to use the maximum of the system 
memory and "balloon" is memory when new domU needs memory.
To resolve it, we have to fix the dom0 memory usage to avoid dom0 
ballooning and crash in our production environnemnt.
The solution seems to pass a parameter at xen boot time (in grub) to 
limit dom0 memory usage : "  dom0_mem=256M "

As anyone encounter this type of problems ?
Is there any other solution than limitting dom0 memory usage ?

Regards

-- 
Frederic Soulier

Administrateur Reseau
Centre de Ressources Informatiques
Universit? Toulouse 1 Sciences Sociales
2 RUE DU DOYEN GABRIEL MARTY
31042 TOULOUSE CEDEX 9
Tel : +33 5 61 63 39 98 / +33 5 61 63 39 98
Fax : +33 5 61 63 37 98   Bureau : AR38 bis
http://cri.univ-tlse1.fr/

On Wed, Feb 20, 2008 at 5:08 PM, Frederic SOULIER
<frederic.soulier at univ-tlse1.fr> wrote:
>
>  I'm having issue with my Centos 5.1 /Xen installation.
>  I'm having  some  dom0 running 2.6.18-53.1.6.el5xen (x86_64).
>  On the dom0 where the load is high (more than 70% of total system memory
>  consumed by dom0 and domU) we have a  lot of  "memory squeeze ".
>  The result is that the domU seems to be blocked (no network/no disk
>  acces/ etc....).
>
>  Looking for a solution in xen user list, it seems the problem come from
>  dom0 xen ballooning.
>  With this option the dom0 attempt to use the maximum of the system
>  memory and "balloon" is memory when new domU needs memory.
>  To resolve it, we have to fix the dom0 memory usage to avoid dom0
>  ballooning and crash in our production environnemnt.
>  The solution seems to pass a parameter at xen boot time (in grub) to
>  limit dom0 memory usage : "  dom0_mem=256M "
>
>  As anyone encounter this type of problems ?
>  Is there any other solution than limitting dom0 memory usage ?
I did not see the problems you are having but I have a set of Xen
hosts and by default I limit the memory usage of the dom0 to 512MB
using the dom0_mem option that you mentioned. In my case the dom0's
are not doing anything so why do they need the memory in the first
place ? That is why I've limited my dom0's like this by default, I
consider this a good practice for these kinds of setups

Regards,
Tim

-- 
Tim Verhoeven - tim.verhoeven.be at gmail.com - 0479 / 88 11 83

Hoping the problem magically goes away by ignoring it is the
"microsoft approach to programming" and should never be allowed.
(Linus Torvalds)