[PATCH] vmscan: skip reclaim_mapped determination if we do not swap

This puts the variables and the way to get to reclaim_mapped in one block.
And allows zone_reclaim or other things to skip the determination (maybe
this whole block of code does not belong into refill_inactive_zone()?)
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/vmscan.c

@@ -1195,9 +1195,47 @@ refill_inactive_zone(struct zone *zone, struct scan_control *sc)
 	struct page *page;
 	struct pagevec pvec;
 	int reclaim_mapped = 0;
-	long mapped_ratio;
-	long distress;
-	long swap_tendency;
+
+	if (unlikely(sc->may_swap)) {
+		long mapped_ratio;
+		long distress;
+		long swap_tendency;
+
+		/*
+		 * `distress' is a measure of how much trouble we're having
+		 * reclaiming pages.  0 -> no problems.  100 -> great trouble.
+		 */
+		distress = 100 >> zone->prev_priority;
+
+		/*
+		 * The point of this algorithm is to decide when to start
+		 * reclaiming mapped memory instead of just pagecache.  Work out
+		 * how much memory
+		 * is mapped.
+		 */
+		mapped_ratio = (sc->nr_mapped * 100) / total_memory;
+
+		/*
+		 * Now decide how much we really want to unmap some pages.  The
+		 * mapped ratio is downgraded - just because there's a lot of
+		 * mapped memory doesn't necessarily mean that page reclaim
+		 * isn't succeeding.
+		 *
+		 * The distress ratio is important - we don't want to start
+		 * going oom.
+		 *
+		 * A 100% value of vm_swappiness overrides this algorithm
+		 * altogether.
+		 */
+		swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
+
+		/*
+		 * Now use this metric to decide whether to start moving mapped
+		 * memory onto the inactive list.
+		 */
+		if (swap_tendency >= 100)
+			reclaim_mapped = 1;
+	}
 
 	lru_add_drain();
 	spin_lock_irq(&zone->lru_lock);
@@ -1207,37 +1245,6 @@ refill_inactive_zone(struct zone *zone, struct scan_control *sc)
 	zone->nr_active -= pgmoved;
 	spin_unlock_irq(&zone->lru_lock);
 
-	/*
-	 * `distress' is a measure of how much trouble we're having reclaiming
-	 * pages.  0 -> no problems.  100 -> great trouble.
-	 */
-	distress = 100 >> zone->prev_priority;
-
-	/*
-	 * The point of this algorithm is to decide when to start reclaiming
-	 * mapped memory instead of just pagecache.  Work out how much memory
-	 * is mapped.
-	 */
-	mapped_ratio = (sc->nr_mapped * 100) / total_memory;
-
-	/*
-	 * Now decide how much we really want to unmap some pages.  The mapped
-	 * ratio is downgraded - just because there's a lot of mapped memory
-	 * doesn't necessarily mean that page reclaim isn't succeeding.
-	 *
-	 * The distress ratio is important - we don't want to start going oom.
-	 *
-	 * A 100% value of vm_swappiness overrides this algorithm altogether.
-	 */
-	swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
-
-	/*
-	 * Now use this metric to decide whether to start moving mapped memory
-	 * onto the inactive list.
-	 */
-	if (swap_tendency >= 100 && sc->may_swap)
-		reclaim_mapped = 1;
-
 	while (!list_empty(&l_hold)) {
 		cond_resched();
 		page = lru_to_page(&l_hold);