Vmstat -s on -current and -10 shows no local-cpu page allocations under Xen -- is that correct?

[Brian Buhrow <buhrow%nfbcal.org@localhost>]

	Hello.  I'm running a series of machines, both Xen VM machines and machines running on
bare metal, and I notice that on my systems running NetBSD-9.99.77, vmstat -s shows that
local-cpu page allocations are never available on the xen VM's, see below.  Yet, on machines
running on bare metal, local-cpu page allocations are often available, which is what I would
expect.  A hand inspection of the sys/uvm kernel sources leads me to suspect this condition
still exists under today's -current and the -10 branch of the source tree.  The Xen VM I'm
showing is configured with 2 VCPU's and the bare metal example I'm showing has 4 CPUs.  My
questions are as follows:

1.  What does the local-cpu stat actually reference?  Is it counting the number of times a CPU
requested a page of memory and a page was available from the local per-cpu free list?

2.  What's special about Xen that makes no  local-cpu allocations available?  
(For the record, I see this behavior on all the 9.99.77 Xen machines I have running.)
As a point of reference, under NetBSD-9.2, local-cpu allocations are available 
much of the time under Xen.

3.  Is this a design decision or is it an actual bug?

-thanks
-Brian

<vmstat-s output from a Xen VM machine>

2908605631 pagealloc desired color avail
242456994 pagealloc desired color not avail
        0 pagealloc local cpu avail
3151062625 pagealloc local cpu not avail
    18763 faults with no memory

<vmstat -s output on actual bare metal hardware>
355234902 pagealloc desired color avail
   250631 pagealloc desired color not avail
310440195 pagealloc local cpu avail
 45045338 pagealloc local cpu not avail
        0 faults with no memory