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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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?

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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