Re: dom0 not seeing all of the assigned memory

[David Vrabel <david.vrabel@citrix.com>]

On 15/03/12 18:33, Konrad Rzeszutek Wilk wrote:
> On Sun, Mar 11, 2012 at 11:20:02PM +0100, Sven Köhler wrote:
>> Am 27.02.2012 20:04, schrieb Roderick Colenbrander:
>>> On Mon, Feb 27, 2012 at 5:34 PM, Henrik Olsson <henrik@fixme.se> wrote:
>>>> On Thu, Feb 23, 2012 at 19:55, David Vrabel <dvrabel@cantab.net> wrote:
>>>>> On 22/02/12 22:19, Henrik Olsson wrote:
>>>>>> Hi, i'm having some trouble with assigning memory to my dom0.
>>>>>>
>>>>>> I've added "dom0_mem=8192M" to the xen command line yet "free -m"
>>>>>> reports only 5686MB total.
>>>>>
>>>>> [    0.000000] Freeing  6f000-100000 pfn range: 593920 pages freed
>>>>> [    0.000000] 1-1 mapping on 6f000->100000
>>>>> [    0.000000] Released 595312 pages of unused memory
>>>>>
>>>>> This accounts for most of your "missing" memory.  To get it back you
>>>>> need to adjust the balloon driver's target to the amount of memory you want.
>>>>>
>>>>> David
>>>>
>>>> Hi, i'm not sure i understand..
>>>>
>>>> I've configured /etc/xen/xend-config.sxp with:
>>>> (dom0-min-mem 8192)
>>>> (enable-dom0-ballooning no)
>>>>
>>>> Shouldn't this disable ballooning? Or do i need to pass some parameter
>>>> somewhere?
>>
>> I have the same problem. I believe this also happens even if the
>> ballooning driver is disabled in dom0 kernel.

Well, yes.  The balloon driver needs to be enabled and a new target set
to get back the memory released during boot.

>>> Make sure you have added the following patch to your Xen if you are
>>> using a recent >=3.1 kernel. Unfortunately it isn't in Xen 4.1.x, but
>>> I guess it should be added to there:
>>> http://xenbits.xen.org/hg/staging/xen-unstable.hg/rev/c56dd5eb0fa2
>>>
>>> See if it helps.
>>
>> I recompiled the hypervisor (this was a patch for the hypervisor,
>> right?) and dom0 only has around 413MB inspite of dom0_mem=512M
>> hypervisor parameter.

You need dom0_mem=max:512M

>> free shows 413MB straight after booting into dom0 (no xend, xenstored or
>> anything xen related stuff has started yet).

This case isn't because of the released memory (since 512M is well below
the MMIO holes that cause lots of released memory) but because page
tables are reserved to the amount of physical ram in the system.

> <sigh> So it sounds like that the kernel should balloon up the released
> amount of memory. David, did we discuss this at some point and agreed that
> was the proper way?

I don't remember discussing it but it's an interesting idea.  Let me
think about it.  It will need to work without the balloon driver (since
it might not exist).

David