unexpected but recoverable situation.  A counter records how often this
event happens but it is easy to miss that this event has occured at
all.  This patch warns once when PG_mlocked is set to prompt debuggers
to check the counter to see how often it is happening.
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>