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

[Pasi Kärkkäinen <pasik@xxxxxx>]

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

-- Pasi


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