On Thu, Oct 20, 2011 at 12:37:34AM +0300, Peter Peltonen wrote:
Hi,
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 swapping:
Did you check the amount of memory in dom0 right after boot? You *might* need to add also "mem=2028M" cmdline option for dom0 linux kernel (vmlinuz).
Also Linux kernel is *supposed* to swap all inactive pages!
So it's normal to have swap being used. If you have *active* swap usage all the time (pages in and out from swap), only then it means you don't have enough memory allocated.
# 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.
dom0 is not supposed to allocate more memory! dom0 is a virtual machine. Free memory goes into Xen hypervisor, check with "xl info" or "xm info".
What am I missing here or is my xen setup acting strangely here?
You're missing the fact that dom0 is a VM.
-- Pasi