Re: [Xen-devel] Free memory reported but not used in new domain creation?

["G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>]

On Mon, Aug 12, 2013 at 2:15 PM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> On Mon, Aug 12, 2013 at 01:46:30PM +0800, G.R. wrote:
>> Hi guys,
>> I need your help understanding this behavior:
>>
>> My host has 8GB RAM installed. Xen reports about 1.8G free memory with
>> three domains running.
>>
>> xl info|grep memory
>> total_memory           : 7887
>> free_memory            : 1833
>>
>> xl list
>> Name                                        ID   Mem VCPUs      State   
>> Time(s)
>> Domain-0                                     0   768     8     r-----     
>> 650.2
>> nas                                          1  3072     2     -b----     
>> 704.0
>> windom                                       3  2047     4     r-----     
>> 520.7
>>
>> Now, when I tried to launch a forth domain with 1G memory assigned,
>> here is the result:
>>
>> xl list
>> Name                                        ID   Mem VCPUs      State   
>> Time(s)
>> Domain-0                                     0   380     8     r-----     
>> 654.1
>> nas                                          1  3072     2     -b----     
>> 706.7
>> windom                                       3  2047     4     r-----     
>> 529.8
>> freebsd                                      5  1024     1     -b----       
>> 0.7
>>
>> xl info|grep memory
>> total_memory           : 7887
>> free_memory            : 1184
>>
>> As you can see, hypervisor is ballooning memory from dom0 instead of
>> allocating from free_memory. If I increase the guest memory of the new
>> domain to 1.5G or 2G. It simply fails to launch, saying something like
>> dom0 memory is below minimal threshold.
>>
>> This gives me the impression that the free_memory is fake. Is it an
>> expected behavior?
>> What are the remaining 1GB memory for?
>>
>> PS: I'm on the xen 4.3.0 release.
>>
>
> Hello,
>
> This is a long-standing bug in xl.
> The workaround is to disable xl autoballooning..
>
> http://wiki.xen.org/wiki/Xen_Best_Practices
>

Thanks for the info. It'll be great if you can point me to the bug /
thread for reference.

I thought I was following that page, but maybe I made some mistake and
the config does not take effect:

xen_commandline        : placeholder
dom0_mem=1G,max:1536M,min:768M,dom0_max_vcpus=6,vpmu=1

If there are any syntax error, shouldn't it raise error?

> -- Pasi
>

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