quoted

If current
node has no memory and other nodes have enough memory.
We can fail to allocate vmemmap pages. But actually it is
suitable to allocate vmemmap pages from other nodes.
Right?

Falling back to a different node would be very suboptimal because then
you would have vmemmap back by remote pages. We do not want that.

... and we even warn when this happens right now:

mm/sparse-vmemmap.c:vmemmap_verify()

-- 
Thanks,

David / dhildenb