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