Line-accurate confirmation (wrap needs 2^31 aggregate events - days
of load; not demonstrable within a verification session):
sys/vm/vm_meter.c:245-253 vcnt(): 'int count' accumulates u_int
   per-CPU vmmeter fields across ncpus; SYSCTL_OUT exports the int
sys/vm/vm_meter.c:259-272 vcnt_intr(): same for v_intr+v_ipi+v_timer
Once the cross-CPU sum (or a single CPU counter at ~10k ctx/s for
~2.5 days) crosses 2^31, vm.stats.sys.* / vm.stats.vm.* export
negative/garbage to systat/top. No in-kernel reader. Correctness
only.