Re: [Xen-devel] Empty memory nodes in VNUMA

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 08/14/2015 11:35 AM, Wei Liu wrote:
> On Fri, Aug 14, 2015 at 11:19:53AM -0400, Boris Ostrovsky wrote:
> > What is the purpose of 'nr_vmemranges < nr_vnodes' test in
> > xc_domain_setvnuma()? Can't we have nodes with no memory?
> >
> > If that's the case, this check will still miss configurations when a node
> > spans multiple memory ranges.
> >
> > For example, this fails:
> >
> > vcpus = 4
> > vnuma = [ [ "pnode=0","size=2048","vcpus=0-1" ],
> >            [ "pnode=1","size=1800" ],
> >            [ "pnode=2","size=0","vcpus=2-3" ],
> >            [ "pnode=3","size=100" ] ]
> >
> > but this
> >
> > vcpus = 4
> > vnuma = [ [ "pnode=0","size=2048","vcpus=0-1" ],
> >            [ "pnode=1","size=1801" ],
> >            [ "pnode=2","size=0","vcpus=2-3" ],
> >            [ "pnode=3","size=100" ] ]
> >
> > does not: because of MMIO hole this will cause a second 1MB range to be
> > created on node 1 (in libxl__vnuma_build_vmemrange_hvm()).
> >
> > Can we drop this check?
> I would say yes. There is certainly such hardware that some NUMA node
> has 0 memory.
>
> Note that this function was written in the early day of vNUMA (4.5).  I
> think that function has the assumption that each vnode has one
> vmemrange.
>
> Try removing that check and see what happens?
I already did --- you think I'd ask without first trying? ;-) Yes, it 
works fine --- one a couple of tests that I tried.
Do you want me to send a patch?

-boris

> But, how far are you willing to go? Do you want system with no
> vmemranges at all (that means, no memory at all)? If so that
> nr_vmemranges == 0 check should also be removed. Just kidding...
>
> Wei.
>
> > -boris

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