vmscan: low order lumpy reclaim also should use PAGEOUT_IO_SYNC

vmscan: low order lumpy reclaim also should use PAGEOUT_IO_SYNC

Commit 33c120ed2843090e2bd316de1588b8bf8b96cbde ("more aggressively use
lumpy reclaim") increased how aggressive lumpy reclaim was by isolating
both active and inactive pages for asynchronous lumpy reclaim on
costly-high-order pages and for cheap-high-order when memory pressure is
high.  However, if the system is under heavy pressure and there are dirty
pages, asynchronous IO may not be sufficient to reclaim a suitable page in
time.

This patch causes the caller to enter synchronous lumpy reclaim for
costly-high-order pages and for cheap-high-order pages when under memory
pressure.

[email protected] said:

Andy added synchronous lumpy reclaim with
c661b078fd62abe06fd11fab4ac5e4eeafe26b6d.  At that time, lumpy reclaim is
not agressive.  His intension is just for high-order users.(above
PAGE_ALLOC_COSTLY_ORDER).

After some time, Rik added aggressive lumpy reclaim with
33c120ed2843090e2bd316de1588b8bf8b96cbde.  His intention was to do lumpy
reclaim when high-order users and trouble getting a small set of
contiguous pages.

So we also have to add synchronous pageout for small set of contiguous
pages.

Cc: Lee Schermerhorn <[email protected]>
Cc: Andy Whitcroft <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Rik van Riel <[email protected]>
Signed-off-by: KOSAKI Motohiro <[email protected]>
Reviewed-by: Minchan Kim <[email protected]>
Reviewed-by: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>