Re: [Xen-devel] [PATCH v6 02/23] xen: move NUMA_NO_NODE to public memory.h as XEN_NUMA_NO_NODE

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.03.15 at 18:01, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 02/03/15 16:50, Jan Beulich wrote:
>>>>> On 02.03.15 at 17:39, <wei.liu2@xxxxxxxxxx> wrote:
>>> On Mon, Mar 02, 2015 at 04:27:25PM +0000, Jan Beulich wrote:
>>>>>>> On 02.03.15 at 17:08, <wei.liu2@xxxxxxxxxx> wrote:
>>>>> On Mon, Mar 02, 2015 at 03:51:37PM +0000, Jan Beulich wrote:
>>>>>>>>> On 02.03.15 at 16:38, <wei.liu2@xxxxxxxxxx> wrote:
>>>>>>> On Mon, Mar 02, 2015 at 03:30:21PM +0000, Ian Campbell wrote:
>>>>>>>> On Mon, 2015-03-02 at 07:04 +0000, Jan Beulich wrote:
>>>>>>>>>>>> Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 02/27/15 5:58 PM >>>
>>>>>>>>>> On 27/02/15 16:51, Wei Liu wrote:
>>>>>>>>>>> During last round review, Andrew wanted me to move this to Xen 
>>>>>>>>>>> public
>>>>>>>>>>> header to avoid reinventing it in libxc. Now this value is used in 
>>>>>>>>>>> libxc
>>>>>>>>>>> patch.
>>>>>>>>>>>
>>>>>>>>>>> But I don't particularly mind whether we move it or not, it's up to 
>>>>>>>>>>> you
>>>>>>>>>>> maintainers to decide.
>>>>>>>>>> It is a sentinel value used in the public ABI.  It should therefore
>>>>>>>>>> appear in the public API.
>>>>>>>>> Which it already does, as XENMEMF_get_node(0). I don't think it needs
>>>>>>>>> particular naming as a new constant, even more that it isn't intended 
>>>>>>>>> to
>>>>>>>>> be used explicitly in any of the memops.
>>>>>>>> IMHO the named constant does seem to make the tools code at least more
>>>>>>>> readable, but without Wei having said where this is to be used I'm not
>>>>>>>> sure where it should live. In particular I'm unsure if/how/where this
>>>>>>>> value gets passed to a hypercall, as opposed to perhaps being used as a
>>>>>>> This is used to fill in vnode_to_pnode array. That array get
>>>>>>> subsequently passed down to hypervisor.
>>>>>> Do we really accept NUMA_NO_NODE to be passed that way?
>>>>>>
>>>>> public/domctl.h:struct xen_domctl_vnuma has vnode_to_pnode array.
>>>> That wasn't my concern - I was rather wondering why we would
>>>> accept any of this array's fields to be set to "no node".
>>>>
>>> If you want to have numa topology exposed to guest but doesn't care
>>> about underly memory affinity?
>> Is this useful for anything in reality?
> 
> Yes.  If there is insufficient memory on real numa nodes, the memory
> could be striped and the guest told that its memory really is scattered
> all over.

I which case it could as well not be handed any vNUMA info at all.

Jan


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