[CentOS-virt] centos6 and xen4 dom0 memory allocation

Wed Oct 19 21:37:34 UTC 2011
Peter Peltonen <peter.peltonen at gmail.com>


This is slightly OT as xen is not officially supported in EL6. But
maybe someone else is running it on centos6 as well and could help me
out here:

I have problems allocating a static amount of memory for my xen dom0.
It seems to reduce when new domUs are created, even though I *think*
ballooning is disabled. Can someone advise me what I'm doing wrong?

I have xen-4.1.1-3 installed from
http://xenbits.xen.org/people/mayoung/EL6.xen on my centos6 server. I
am running 2.6.32-131.12.1.el6.xendom0.x86_64 kernel available from
the same place. 'xl info' reports about available memory as follows:

total_memory           : 24567
free_memory            : 3698
xen_commandline        : dom0_mem=2048M

and in xend-config.sxp I have:

(dom0-min-mem 256)
(enable-dom0-ballooning no)
(total_available_memory 0)

Now one would think that I should have 2048M memory for dom0, right? I
started from there, but when starting domUs it has been reduced to
1140M even though I think ballooning is disabled and there is free
memory available? And the weird thing is that dom0 has done some

# free -mt
             total       used       free     shared    buffers     cached
Mem:          1140       1052         88          0          2         12
-/+ buffers/cache:       1038        102
Swap:         8194         85       8109
Total:        9335       1138       8197

Shutting down domUs and making more memory available does not reverse
the effect, dom0 does not allocate more memory.

What am I missing here or is my xen setup acting strangely here?

Best regards,