Re: libxl: calculating free pages in libvirt

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Jun 06, 2013 at 03:53:13PM +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. You can see an example of that, for instance, looking at the
> output_physinfo() function in tools/libxl/xl_cmdimpl.c (in the Xen
> codebase, of course :-) ).
> 
> Said commit is from last May, and the claim mechanism altogether --which
> includes adding the outstanding_pages field to the libxl_physinfo struct
> in libxl-- was introduced during the 4.3 development cycle.
> 
> So, forgive the possibly dumb question, but what's the preferred way to
> fix this in libvirt, without breaking build with old libxl versions?
> (Provided this is something libvirt cares about, does it?)
> 
> 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?
> If no, should we add it?

I think we missed it. I remember thinking about it, but I can't recall
what I didn't submit. It certainly should be added.

And I think that would fix the build of old libxl against new libvirt.
Or vice-versa (if libxl supported the claim operation).
> 
> Thanks and 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)
>