[PATCH 4/4] vmscan: delegate page cleaning io to flusher thread if VM pressure is low

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

Even if pageout() is called from direct reclaim, we can delegate io to
flusher thread if vm pressure is low.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
 mm/vmscan.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8b78b49..eab6028 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -623,6 +623,13 @@ static enum page_references page_check_references(struct page *page,
 	if (current_is_kswapd())
 		return PAGEREF_RECLAIM_CLEAN;
 
+	/*
+	 * Now VM pressure is not so high. then we can delegate
+	 * page cleaning to flusher thread safely.
+	 */
+	if (!sc->order && sc->priority > DEF_PRIORITY/2)
+		return PAGEREF_RECLAIM_CLEAN;
+
 	return PAGEREF_RECLAIM;
 }
 
-- 
1.6.5.2