vmstat's entries type

[Paul Allen]

Surely all you need to do is a cheap crit_enter,crit_exit 
while updating the 64-bit per cpu counters.  and on
a 64-bit arch you skip the crit_enter,crit_exit.

Seriously this is a bike shed.  We can summarize it thus:
statistics should be maintained in 64-bit counters, these
counters should be per-cpu and consistent in that context,
nothing else should appear on the critical path.

**end of story**

         Paul

p.s., and as a general of thumb, if a per-cpu solution
doesn't explode in complexity/memory usage it should be
preferred over a mutex by default.