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

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.


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