CP-309998: ignore small amount of pages in other nodes

rrdp-squeezed currently has a threshold of >4096 to count the number
of nodes. This is to ignore small number of internal data structures
that xen or other kernel devices may sometimes allocate for the VM
outside the node where the VM's main memory is allocated.

This is a temporary fix until we account in CP-311303 about these
small number of pages that sometimes appear out of the VM's main node.
In experiments, it's usually a single-digit number like 1. The maximum
number observed was around ~2200 pages.

Without this fix, the VM.numa_nodes calculation is different of the
one returned by rrdp-squeezed, and VM.numa_nodes is over-sensitive to
these small number of pages in other nodes.

Signed-off-by: Marcus Granado <marcus.granado@cloud.com>

Author: mg12

ocaml/libs/xenctrl-ext/xenctrlext.ml

@@ -156,7 +156,7 @@ module DomainNuma = struct
       let nodes =
         Array.fold_left
           (fun n pages ->
-            if pages > 0L then
+            if pages > 4096L then
               n + 1
             else
               n