[CentOS-virt] centos6 and xen4 dom0 memory allocation
pasik at iki.fi
Sat Oct 22 09:21:17 EDT 2011
On Thu, Oct 20, 2011 at 12:37:34AM +0300, Peter Peltonen wrote:
> 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
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.
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