[libvirt] libxl: calculating free pages in libvirt

[Dario Faggioli]

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?

> > For other features added within this last dev cycle, libxl has a
> > `#define LIBXL_HAVE_<foo>' (e.g., LIBXL_HAVE_DOMAIN_NODEAFFINITY), but I
> > don't see one for this particular field... Konrad, Ian, am I missing it?
> 
> I don't think so, we seem to have forgotten.
> 
> > If no, should we add it?
> 
> Yes, I think that would be wise.
> 
Ok, sending a patch (for libxl) then.

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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