Re: [Xen-users] xen 4.1 missing memory

[Eduardo Bragatto <eduardo@xxxxxxxxxxxx>]

Hello Fajar,

I know this is an old thread, but I have a similar question and unlike the guys who were ignoring your advice, I actually did everything I believe to be necessary to control the usage of RAM memory by dom0 -- and I still see memory missing (precisely 279MB on four PowerEdge R710 servers running "2 x E5620" with 24GB each).

This is my scenario:

0. I'm running Xen 3.4.3 (from GITCO repo's) and different kernel releases, but all same version: 2.6.18 (from CentOS: kernel-xen-2.6.18-194.32.1.el5 , kernel-xen-2.6.18-238.9.1.el5 and kernel-xen-2.6.18-274.3.1.el5);

1. I have dom0_mem=512M on my boot parameters;

2. I have xend-config.xsp configured with: (dom0-min-mem 512) AND (enable-dom0-ballooning no);

3. There are 4 different boxes and they all are missing precisely 279MB immediately after boot, regardless of any VM running or not (besides Dom0, of course);

Here are some examples:

[root@hypervisor01]# xm list ; xm info | grep mem
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0   512    16     r----- 1955257.4
Domain-1                                     10 23500    16     r----- 11442974.1
total_memory           : 24563
free_memory            : 272
node_to_memory         : node0:272
[root@hypervisor01~]# echo '512+23500+272' | bc ### adding Dom0 + Dom1 + "free_memory" should give me the same number as "total_memory"
24284
[root@hypervisor01~]# echo '24563-24284' | bc ### however it doesn't, I'm missing 279MB
279

And here, a hypervisor with no VMs running at all, just after a reboot:

[root@hypervisor02 ~]# xm list ; xm info | grep mem
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0   512    16     r----- 1195310.3
total_memory           : 24563
free_memory            : 23772
node_to_memory         : node0:23772
[root@hypervisor02 ~]# echo '512+23772' | bc ### Again, adding Dom0 "free_memory" should give me the same number as "total_memory"
24284
[root@hypervisor02 ~]# echo '24563-24284' | bc ### And again, I'm missing 279MB
279


Is there any explanation as to where those 279MB are going to?

To be honest, it doesn't bother me that much that I have just a bit more than 1% of "total_memory" simply "disappearing", but the lack of an explanation does take my sleep.

Any thoughts?

Kind regards,
Eduardo Bragatto

On Thu, Aug 18, 2011 at 3:34 AM, Fajar A. Nugraha <list@xxxxxxxxx> wrote:

On Thu, Aug 18, 2011 at 1:02 PM, Ian Tobin <itobin@xxxxxxxxxxxxx> wrote:
> Hey,
>
> I set the dom0 min men to 512m in xend-config.sxp and ballooning is already enabled.  I rebooted and it initially shows 512m but one the vms are booted it drops to 256 .
>
> Any other thoughts?

DISABLE ballooning?

--
Fajar

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