linux-kernel - [patch 2/2] mm: vmscan: drop nr_force_scan[] from get_scan

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Date:	Thu, 11 Aug 2011 22:31:55 +0200
From:	Johannes Weiner <jweiner@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, Ying Han <yinghan@...gle.com>,
	Balbir Singh <bsingharora@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Mel Gorman <mel@....ul.ie>
Subject: [patch 2/2] mm: vmscan: drop nr_force_scan[] from get_scan_count

The nr_force_scan[] tuple holds the effective scan numbers for anon
and file pages in case the situation called for a forced scan and the
regularly calculated scan numbers turned out zero.

However, the effective scan number can always be assumed to be
SWAP_CLUSTER_MAX right before the division into anon and file.  The
numerators and denominator are properly set up for all cases, be it
force scan for just file, just anon, or both, to do the right thing.

Signed-off-by: Johannes Weiner <jweiner@...hat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Ying Han <yinghan@...gle.com>
Cc: Balbir Singh <bsingharora@...il.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc: Mel Gorman <mel@....ul.ie>
---
 mm/vmscan.c |   24 ++----------------------
 1 files changed, 2 insertions(+), 22 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 96061d7..45f0986 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1831,7 +1831,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
 	enum lru_list l;
 	int noswap = 0;
 	bool force_scan = false;
-	unsigned long nr_force_scan[2];
 
 	/* kswapd does zone balancing and need to scan this zone */
 	if (scanning_global_lru(sc) && current_is_kswapd())
@@ -1846,8 +1845,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
 		fraction[0] = 0;
 		fraction[1] = 1;
 		denominator = 1;
-		nr_force_scan[0] = 0;
-		nr_force_scan[1] = SWAP_CLUSTER_MAX;
 		goto out;
 	}
 
@@ -1864,8 +1861,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
 			fraction[0] = 1;
 			fraction[1] = 0;
 			denominator = 1;
-			nr_force_scan[0] = SWAP_CLUSTER_MAX;
-			nr_force_scan[1] = 0;
 			goto out;
 		}
 	}
@@ -1914,11 +1909,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
 	fraction[0] = ap;
 	fraction[1] = fp;
 	denominator = ap + fp + 1;
-	if (force_scan) {
-		unsigned long scan = SWAP_CLUSTER_MAX;
-		nr_force_scan[0] = div64_u64(scan * ap, denominator);
-		nr_force_scan[1] = div64_u64(scan * fp, denominator);
-	}
 out:
 	for_each_evictable_lru(l) {
 		int file = is_file_lru(l);
@@ -1927,20 +1917,10 @@ out:
 		scan = zone_nr_lru_pages(zone, sc, l);
 		if (priority || noswap) {
 			scan >>= priority;
+			if (!scan && force_scan)
+				scan = SWAP_CLUSTER_MAX;
 			scan = div64_u64(scan * fraction[file], denominator);
 		}
-
-		/*
-		 * If zone is small or memcg is small, nr[l] can be 0.
-		 * This results no-scan on this priority and priority drop down.
-		 * For global direct reclaim, it can visit next zone and tend
-		 * not to have problems. For global kswapd, it's for zone
-		 * balancing and it need to scan a small amounts. When using
-		 * memcg, priority drop can cause big latency. So, it's better
-		 * to scan small amount. See may_noscan above.
-		 */
-		if (!scan && force_scan)
-			scan = nr_force_scan[file];
 		nr[l] = scan;
 	}
 }
-- 
1.7.6

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