[CentOS-virt] Issue with dom0 xen ballooning

Frederic SOULIER frederic.soulier at univ-tlse1.fr
Thu Feb 21 15:44:47 UTC 2008

Tim Verhoeven a écrit :
> 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
I think you're totally right !!

Dom0 ballooning is good for personnal computer uses (for example on my 
where we want maximum memory on dom0 when domUs are down.

By default, in the centos xen kernel package,  the limit parameter 
(dom0_mem) is not set in grub.conf,
perhaps it could be a good job to insert this parameter with small value 
(256) directly in this
xen kernel package distribution since centos is more server relevant 
than laptop ............


Frederic Soulier

Administrateur Reseau
Centre de Ressources Informatiques
Université Toulouse 1 Sciences Sociales
Tel : +33 5 61 63 39 98 / +33 5 61 63 39 98
Fax : +33 5 61 63 37 98   Bureau : AR38 bis

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