[PATCH] vmscan: aligned scan batching

[Wu Fengguang <fengguang.wu@intel.com>]

>  - pass nr_to_scan into isolate_pages() directly instead
>    using SWAP_CLUSTER_MAX

This patch will make sure nr_to_scan==SWAP_CLUSTER_MAX :)

Thanks,
Fengguang
---
vmscan: aligned scan batching

Make sure ->isolate_pages() always scans in unit of SWAP_CLUSTER_MAX.

CC: Rik van Riel <riel@redhat.com>
CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 mm/vmscan.c |   20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

--- linux-mm.orig/mm/vmscan.c	2009-12-06 13:13:28.000000000 +0800
+++ linux-mm/mm/vmscan.c	2009-12-06 13:31:21.000000000 +0800
@@ -1572,15 +1572,11 @@ static void get_scan_ratio(struct zone *
 static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
 				       unsigned long *nr_saved_scan)
 {
-	unsigned long nr;
+	unsigned long nr = *nr_saved_scan + nr_to_scan;
+	unsigned long rem = nr & (SWAP_CLUSTER_MAX - 1);
 
-	*nr_saved_scan += nr_to_scan;
-	nr = *nr_saved_scan;
-
-	if (nr >= SWAP_CLUSTER_MAX)
-		*nr_saved_scan = 0;
-	else
-		nr = 0;
+	*nr_saved_scan = rem;
+	nr -= rem;
 
 	return nr;
 }
@@ -1592,7 +1588,6 @@ static void shrink_zone(int priority, st
 				struct scan_control *sc)
 {
 	unsigned long nr[NR_LRU_LISTS];
-	unsigned long nr_to_scan;
 	unsigned long percent[2];	/* anon @ 0; file @ 1 */
 	enum lru_list l;
 	unsigned long nr_reclaimed = sc->nr_reclaimed;
@@ -1625,11 +1620,8 @@ static void shrink_zone(int priority, st
 					nr[LRU_INACTIVE_FILE]) {
 		for_each_evictable_lru(l) {
 			if (nr[l]) {
-				nr_to_scan = min_t(unsigned long,
-						   nr[l], SWAP_CLUSTER_MAX);
-				nr[l] -= nr_to_scan;
-
-				nr_reclaimed += shrink_list(l, nr_to_scan,
+				nr[l] -= SWAP_CLUSTER_MAX;
+				nr_reclaimed += shrink_list(l, SWAP_CLUSTER_MAX,
 							    zone, sc, priority);
 			}
 		}