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Re: [Xen-users] Memory not seen in Dom0



On Sat, Nov 07, 2009 at 05:50:45AM -0500, maillists0@xxxxxxxxx wrote:
>    I have a machine with 64G of ram. Running CentOS 5.4 with kernel
>    2.6.18-164, I only see 32G in /proc/meminfo. All 64G show up for the stock
>    kernel. There are no vm's running.
> 
>    I'm new to xen, so my first question is: is this normal? If not, anyone
>    know what the issue might be? Any help or pointers to a doc is
>    appreciated.

Dom0 shouldn't see all the memory !!
You should limit dom0 memory to, say, 1 GB.

Add dom0_mem=1G option for xen.gz in /boot/grub/grub.conf and reboot.

then your dom0 should have around 1 GB in /proc/meminfo.

You can check the Xen hypervisor memory info with "xm info". It'll list
the hypervisor available memory.

And "xm list" will list how much memory each domain/guest is using.

If you have full amount (32G or 64G) of memory visible to dom0 linux
kernel, then linux will set network, memory etc defauls based on that 
(huge) boot time amount of memory.. and then when you create guests,
that dom0 memory will be "ballooned" down, and later when you have
much smaller amount of memory in dom0, it'll have problems since many
internal kernel parameters were based on having 32G or 64G of memory..
and weird things start to happen.

So it's best to limit and dedicate for example 1 GB of memory to dom0
and prevent ballooning that way.

Xen always dedicated physical memory to each guest.. dom0 is also a guest.

-- Pasi



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