Re: [Xen-devel] [PATCH] Fix hypervisor crash with unpopulated NUMA nodes

[Andre Przywara <andre.przywara@xxxxxxx>]

Jan Beulich wrote:
> > > > Andre Przywara <andre.przywara@xxxxxxx> 07.10.09 11:45 >>>
> > on NUMA systems with memory-less nodes Xen crashes quite early in the 
> > hypervisor (while initializing the heaps). This is not an issue if this 
> > happens to be the last node, but "inner" nodes trigger this reliably.
> > On multi-node processors it is much more likely to leave a node unequipped.
> > The attached patch fixes this by enumerating the node via the 
> > node_online_map instead of counting from 0 to num_nodes.
> While I do not see anything wrong with the patch, I still wonder why it
> would be needed: It seems to indicate that node_online_map represents
> only nodes with memory, but imo should be representing nodes with
> memory or processors (leaving aside pure I/O nodes for the moment).
> So perhaps there's rather a problem with the setup of node_online_map 
> somewhere?
Yes, because the map creation is callback driven by ACPI code.
The BIOS of my machine is omitting the memory entries for memory-less 
nodes, so there is no callback triggered for these nodes. Nevertheless 
Xen uses the SRAT provided node numbers, this creates the hole.
(My setup: 2 + 0 + 2 + 0 GB per node, Xen sees two nodes named 0 and 2).
I agree that should be changed (that is what I meant with "will rework 
later"), not only because the "lonely" cores will simply be added to 
another node. But since I will be not in the office for the next two 
weeks I would like to get this patch applied for the time being.
Regards,
Andre.

--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448 3567 12
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