vmscan: tracing: add trace events for kswapd wakeup, sleeping and direct reclaim

vmscan: tracing: add trace events for kswapd wakeup, sleeping and direct reclaim

Add two trace events for kswapd waking up and going asleep for the
purposes of tracking kswapd activity and two trace events for direct
reclaim beginning and ending.  The information can be used to work out how
much time a process or the system is spending on the reclamation of pages
and in the case of direct reclaim, how many pages were reclaimed for that
process.  High frequency triggering of these events could point to memory
pressure problems.

Signed-off-by: Mel Gorman <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Acked-by: Larry Woodman <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Michael Rubin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>