From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wei Liu <wei.liu2@citrix.com>
Subject: Re: Empty memory nodes in VNUMA
Date: Fri, 14 Aug 2015 16:44:35 +0100
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To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>, Dario Faggioli <dario.faggioli@citrix.com>, Wei Liu <wei.liu2@citrix.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Ian Campbell <ian.campbell@citrix.com>
List-Id: xen-devel@lists.xenproject.org

On Fri, Aug 14, 2015 at 11:38:43AM -0400, Boris Ostrovsky wrote:
> 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.
> 

Cool. :-)

> Do you want me to send a patch?
> 

Sure. Much appreciated.

Wei.

> -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