[libvirt] libxl: calculating free pages in libvirt

[Jim Fehlig]

Dario Faggioli wrote:
> On gio, 2013-06-06 at 14:59 +0100, Ian Campbell wrote:
>   
>> On Thu, 2013-06-06 at 15:53 +0200, Dario Faggioli wrote:
>>     
>>> Hi Jim,
>>>
>>> As I told you in Dublin, I'm looking into libvirt a bit, with the main
>>> purpose of implementing the NUMA interface for the libxl driver.
>>>
>>> While at it I noticed that libxlNodeGetFreeMemory() uses the value
>>> contained in phy_info.free_pages to check how many pages of free memory
>>> we have.
>>>
>>> However, starting from (Xen's git) commit bec8f17e, the number of free
>>> pages should be computed like this:
>>>
>>>  (phy_info.free_pages - phy_info.outstanding_pages)
>>>
>>> to take the memory claiming mechanism introduced by Oracle properly into
>>> account.
>>>       
>> This only really matters if libvirt wants to coexist on a host with
>> toolstacks which use claim, otherwise outstanding pages will never be
>> non-zero. I don't know if coexistence is a goal or not.
>>
>>     
> Sure, all this is important only if having it is
> important/interesting... Jim?
>   

It would be preferable if libvirt and xl coexisted nicely.  No need for
them to inter-operate (e.g. start a vm with libvirt then manage it with
xl), but managing some with xl and others with libvirt should be a goal,
I think :-/.  If nothing else, it seems useful for troubleshooting.  I
wouldn't want to advise a user to try xl when things are failing for
them with libvirt, only to find that afterwards their libvirt no longer
worked at all.

Regards,
Jim