[PATCH 2/2] vmscan: don't subtraction of unsined

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

'slab_reclaimable' and 'nr_pages' are unsigned. so, subtraction is
unsafe.

Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
 mm/vmscan.c |   18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c927948..b1a90f8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2612,6 +2612,8 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 	slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
 	if (slab_reclaimable > zone->min_slab_pages) {
 		unsigned long lru_pages = zone_reclaimable_pages(zone);
+		unsigned long srec_new;
+
 		/*
 		 * shrink_slab() does not currently allow us to determine how
 		 * many pages were freed in this zone. So we take the current
@@ -2622,17 +2624,21 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 		 * Note that shrink_slab will free memory on all zones and may
 		 * take a long time.
 		 */
-		while (shrink_slab(sc.nr_scanned, gfp_mask, lru_pages) &&
-			zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
-				slab_reclaimable - nr_pages)
-			;
+		for (;;) {
+			if (!shrink_slab(sc.nr_scanned, gfp_mask, lru_pages))
+				break;
+			srec_new = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
+			if (srec_new + nr_pages <= slab_reclaimable)
+				break;
+		}
 
 		/*
 		 * Update nr_reclaimed by the number of slab pages we
 		 * reclaimed from this zone.
 		 */
-		sc.nr_reclaimed += slab_reclaimable -
-			zone_page_state(zone, NR_SLAB_RECLAIMABLE);
+		srec_new = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
+		if (srec_new < slab_reclaimable)
+			sc.nr_reclaimed += slab_reclaimable - srec_new;
 	}
 
 	p->reclaim_state = NULL;
-- 
1.6.5.2



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