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SubjectRe: [PATCH x86/mm UPDATED] x86-64, NUMA: Fix distance table handling

On Thu, Mar 03, 2011 at 12:07:10PM -0800, David Rientjes wrote:
> The new emulation code needs to remove the assumption that node 0 always
> is online and become more robust since there's no such restriction in the
> ACPI spec.

Yeah, indeed, that's possible. ACPI spec isn't really the deciding
factor here. The node IDs are purely software and a system is
required to have at least one node, so it seems reasonable to require
node 0 to be always online - or even to require all online node IDs to
be consecutive starting from 0. The only reason we may have holes in
node IDs now is because PXM -> nid mapping isn't released for empty
memory-only nodes.

The biggest downside of deferring checks for this type of rare
conditions to upper layers when not strictly necessary is that it
tends to lead to one-off bugs which trigger very infrequently.

That said, maybe we're already too deep toward that direction and it's
much easier to weed out the assumptions that node0 is always online.



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