linux-kernel - [PATCH 06/25] mm, vmscan: Avoid a second search through zones checking if compaction is required

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Date:	Mon,  8 Jun 2015 14:56:12 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Linux-MM <linux-mm@...ck.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 06/25] mm, vmscan: Avoid a second search through zones checking if compaction is required

This patch removes an unnecessary loop.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/vmscan.c | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index f0eed2e6883c..975c315f1bf5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3182,30 +3182,25 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 				 */
 				clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
 				clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
+
+				/*
+				 * If any zone is currently balanced then kswapd will
+				 * not call compaction as it is expected that the
+				 * necessary pages are already available.
+				 */
+				if (pgdat_needs_compaction &&
+						zone_watermark_ok(zone, order,
+							low_wmark_pages(zone),
+							*classzone_idx, 0)) {
+					pgdat_needs_compaction = false;
+				}
+
 			}
 		}
 
 		if (i < 0)
 			goto out;
 
-		for (i = 0; i <= end_zone; i++) {
-			struct zone *zone = pgdat->node_zones + i;
-
-			if (!populated_zone(zone))
-				continue;
-
-			/*
-			 * If any zone is currently balanced then kswapd will
-			 * not call compaction as it is expected that the
-			 * necessary pages are already available.
-			 */
-			if (pgdat_needs_compaction &&
-					zone_watermark_ok(zone, order,
-						low_wmark_pages(zone),
-						*classzone_idx, 0))
-				pgdat_needs_compaction = false;
-		}
-
 		/*
 		 * If we're getting trouble reclaiming, start doing writepage
 		 * even in laptop mode.
-- 
2.3.5

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