Update VM's numa state

[lindig]

The missing bits: when xenopsd reports a new VM state; update its numa state in xapi accordingly.

[edwintorok]

Would Array.mapi simplify this code? (followed by Array.to_list)

[lindig]

Yes. Let's mapi do the work.

[psafont]

using Array.mapi means a new array is allocated, do we want that?

One way to avoid it would be:

                numa.Xenctrlext.DomainNuma.memory
                |> Array.to_seq
                |> Seq.mapi (fun i mem -> (i, mem))
                |> List.of_seq

[lindig]

Is this cheaper? I don't understand the cost of Seq well.

[psafont]

Seq is a lazy structure, and the transformations only get executed for building the end result, so instead of creating a new array and a new list, this should create a new list only (and the closures for doing the transformation for each value)

[contificate]

I expect the intermediary closures will end up using more space than creating a fresh array: the List.of_seq amounts to consecutively forcing the sequence (applying the closures that arise from the partial application of the next array index). The previous closures will probably be around until the next minor sweep.

I'm actually really fond of the original version of the code. It avoids the space problem entirely.