Re: [Xen-devel] Memory allocation going seriously wonky on 4.1.1

[Anthony Wright <anthony@xxxxxxxxxxxxxxx>]

On 06/10/2011 16:48, Konrad Rzeszutek Wilk wrote:
> On Thu, Oct 06, 2011 at 01:57:32PM +0100, Anthony Wright wrote:
>> On 03/10/2011 20:09, Konrad Rzeszutek Wilk wrote:
>>> On Mon, Oct 03, 2011 at 02:45:36PM +0100, Anthony Wright wrote:
>>>> On 01/10/2011 13:07, Pasi Kärkkäinen wrote:
>>>>> On Fri, Sep 30, 2011 at 04:07:06PM +0100, Anthony Wright wrote:
>>>>>> I have a machine with 16GB of RAM running 32 bit xen 4.1.1 with Dom0
>>>>>> running a 3.0.4 linux kernel and 23 paravirtualized DomUs.
>>>>>>
>>>>> Hey,
>>>>>
>>>>> Why 32bit Xen? I think all (most?) hypervisor testing happens with 64bit 
>>>>> Xen.
>>>>> Note that you can still have 32bit dom0 kernel with 64b hypervisor.
>>>> I'm going to investigate 64 bit xen on a 32 bit Dom0 soon, but as to the
>>>> 32 xen, I work quite a lot with older hardware and Xen since it does
>>>> paravirtualisation, and it's a really good way to re-use old hardware.
>>>>>> As the free ram gets to 2391 MB free the system behaves as if it's got
>>>>>> no more ram, and starts grabbing ram from Dom0, before getting even more
>>>>>> confused and failing to start DomUs and eventually crashing the whole
>>>>>> machine. I have attached a tarball with the output of xl dmesg, xl info
>>>>>> & xl list at various points.
>>>>>>
>>>>> - Do you use dom0_mem= parameter for Xen? 
>>>>> - Did you disable dom0 ballooning? 
>>>>>
>>>>> http://wiki.xen.org/xenwiki/XenBestPractices
>>>> I was already using the dom0_mem= parameter on the xen hypervisor, but I
>>>> disabled dom0 ballooning (enable-dom0-ballooning no), and just for good
>>>> measure I also set (dom0-min-mem 2000). This had no effect, when I
>>>> increase the 10-4 memory requirements, on restart the Dom0 memory is
>>>> reduced to 1713MB and xl info reports 2391MB free.
>>>>>> Stage 1
>>>>>> Everything is fine, Dom0 has 2000MB according to xl list, and 'xl info'
>>>>>> says there is 2405MB free.
>>>>> - How much memory did dom0 initially have? 
>>>>> - Did you use mem= parameter for dom0 kernel (vmlinuz) ?
>>>>>
>>>>> See: http://wiki.xen.org/xenwiki/Linux_30_bugs
>>>> dom0 starts with 2000MB.
>>>> I didn't use mem= on the linux kernel - I thought it wasn't neccessary.
>>> It is if your kernel does not have these two patches:
>>>
>>>     xen: use maximum reservation to limit amount of usable RAM
>>>     xen/e820: if there is no dom0_mem=, don't tweak extra_pages.
>>>
>>> .. oh and you also need to update the hypervisor to include:
>>> "
>>>     For dom0, this requires at patch to Xen ('x86: use 'dom0_mem' to limit
>>>     the number of pages for dom0') (c/s 23790)
>>> "
>>>
>>> Grrr.. Let me update the 3.0 bug-list
>> I applied the two kernel patches, but get similar results, dom0 still
>> gets ballooned down (even more agressively) despite having
>> dom0_mem=2000, dom0-min-mem=2000 and enable-dom0-ballooning set to 0.
>>
>> I couldn't find the xen patch, could you point me in the right direction.
> Google seems to find it.
Ooopps, sorry I completely missed that. I'll try with that patch too.

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