vmscan: simplify shrink_inactive_list()

Now, max_scan of shrink_inactive_list() is always passed less than
SWAP_CLUSTER_MAX.  then, we can remove scanning pages loop in it.  This
patch also help stack diet.

detail
 - remove "while (nr_scanned < max_scan)" loop
 - remove nr_freed (now, we use nr_reclaimed directly)
 - remove nr_scan (now, we use nr_scanned directly)
 - rename max_scan to nr_to_scan
 - pass nr_to_scan into isolate_pages() directly instead
   using SWAP_CLUSTER_MAX

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michael Rubin <mrubin@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -1136,15 +1136,21 @@ static int too_many_isolated(struct zone *zone, int file,
  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
  * of reclaimed pages
  */
-static unsigned long shrink_inactive_list(unsigned long max_scan,
+static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
 			struct zone *zone, struct scan_control *sc,
 			int priority, int file)
 {
 	LIST_HEAD(page_list);
 	struct pagevec pvec;
-	unsigned long nr_scanned = 0;
+	unsigned long nr_scanned;
 	unsigned long nr_reclaimed = 0;
 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
+	struct page *page;
+	unsigned long nr_taken;
+	unsigned long nr_active;
+	unsigned int count[NR_LRU_LISTS] = { 0, };
+	unsigned long nr_anon;
+	unsigned long nr_file;
 
 	while (unlikely(too_many_isolated(zone, file, sc))) {
 		congestion_wait(BLK_RW_ASYNC, HZ/10);
@@ -1159,33 +1165,25 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
 
 	lru_add_drain();
 	spin_lock_irq(&zone->lru_lock);
-	do {
-		struct page *page;
-		unsigned long nr_taken;
-		unsigned long nr_scan;
-		unsigned long nr_freed;
-		unsigned long nr_active;
-		unsigned int count[NR_LRU_LISTS] = { 0, };
-		int mode = sc->lumpy_reclaim_mode ? ISOLATE_BOTH : ISOLATE_INACTIVE;
-		unsigned long nr_anon;
-		unsigned long nr_file;
 
 	if (scanning_global_lru(sc)) {
-			nr_taken = isolate_pages_global(SWAP_CLUSTER_MAX,
-							&page_list, &nr_scan,
-							sc->order, mode,
+		nr_taken = isolate_pages_global(nr_to_scan,
+			&page_list, &nr_scanned, sc->order,
+			sc->lumpy_reclaim_mode ?
+				ISOLATE_BOTH : ISOLATE_INACTIVE,
 			zone, 0, file);
-			zone->pages_scanned += nr_scan;
+		zone->pages_scanned += nr_scanned;
 		if (current_is_kswapd())
 			__count_zone_vm_events(PGSCAN_KSWAPD, zone,
-						       nr_scan);
+					       nr_scanned);
 		else
 			__count_zone_vm_events(PGSCAN_DIRECT, zone,
-						       nr_scan);
+					       nr_scanned);
 	} else {
-			nr_taken = mem_cgroup_isolate_pages(SWAP_CLUSTER_MAX,
-							&page_list, &nr_scan,
-							sc->order, mode,
+		nr_taken = mem_cgroup_isolate_pages(nr_to_scan,
+			&page_list, &nr_scanned, sc->order,
+			sc->lumpy_reclaim_mode ?
+				ISOLATE_BOTH : ISOLATE_INACTIVE,
 			zone, sc->mem_cgroup,
 			0, file);
 		/*
@@ -1219,8 +1217,7 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
 
 	spin_unlock_irq(&zone->lru_lock);
 
-		nr_scanned += nr_scan;
-		nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
+	nr_reclaimed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
 
 	/*
 	 * If we are direct reclaiming for contiguous pages and we do
@@ -1228,7 +1225,7 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
 	 * for IO to complete. This will stall high-order allocations
 	 * but that should be acceptable to the caller
 	 */
-		if (nr_freed < nr_taken && !current_is_kswapd() &&
+	if (nr_reclaimed < nr_taken && !current_is_kswapd() &&
 			sc->lumpy_reclaim_mode) {
 		congestion_wait(BLK_RW_ASYNC, HZ/10);
 
@@ -1239,16 +1236,13 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
 		nr_active = clear_active_flags(&page_list, count);
 		count_vm_events(PGDEACTIVATE, nr_active);
 
-			nr_freed += shrink_page_list(&page_list, sc,
-							PAGEOUT_IO_SYNC);
+		nr_reclaimed += shrink_page_list(&page_list, sc, PAGEOUT_IO_SYNC);
 	}
 
-		nr_reclaimed += nr_freed;
-
 	local_irq_disable();
 	if (current_is_kswapd())
-			__count_vm_events(KSWAPD_STEAL, nr_freed);
-		__count_zone_vm_events(PGSTEAL, zone, nr_freed);
+		__count_vm_events(KSWAPD_STEAL, nr_reclaimed);
+	__count_zone_vm_events(PGSTEAL, zone, nr_reclaimed);
 
 	spin_lock(&zone->lru_lock);
 	/*
@@ -1281,8 +1275,6 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
 	__mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
 	__mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
 
-  	} while (nr_scanned < max_scan);
-
 done:
 	spin_unlock_irq(&zone->lru_lock);
 	pagevec_release(&pvec);