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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew

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