[PATCH 1/4] vmscan: delegate pageout io to flusher thread if current is kswapd

[KOSAKI Motohiro]

Now, vmscan pageout() is one of IO throuput degression source.
Some IO workload makes very much order-0 allocation and reclaim
and pageout's 4K IOs are making annoying lots seeks.

At least, kswapd can avoid such pageout() because kswapd don't
need to consider OOM-Killer situation. that's no risk.

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

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3ff3311..d392a50 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -614,6 +614,13 @@ static enum page_references page_check_references(struct page *page,
 	if (referenced_page)
 		return PAGEREF_RECLAIM_CLEAN;
 
+	/*
+	 * Delegate pageout IO to flusher thread. They can make more
+	 * effective IO pattern.
+	 */
+	if (current_is_kswapd())
+		return PAGEREF_RECLAIM_CLEAN;
+
 	return PAGEREF_RECLAIM;
 }
 
-- 
1.6.5.2



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