vmscan: protect reading of reclaim_stat with lru_lock

Rik van Riel pointed out reading reclaim_stat should be protected
lru_lock, otherwise vmscan might sweep 2x much pages.

This fault was introduced by

  commit 4f98a2fee8acdb4ac84545df98cccecfd130f8db
  Author: Rik van Riel <riel@redhat.com>
  Date:   Sat Oct 18 20:26:32 2008 -0700

    vmscan: split LRU lists into anon & file sets

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 11 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1b4e4a597caa..a3d669f8e25e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1628,6 +1628,13 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
         }
 
         /*
+         * With swappiness at 100, anonymous and file have the same priority.
+         * This scanning priority is essentially the inverse of IO cost.
+         */
+        anon_prio = sc->swappiness;
+        file_prio = 200 - sc->swappiness;
+
+        /*
          * OK, so we have swap space and a fair amount of page cache
          * pages.  We use the recently rotated / recently scanned
          * ratios to determine how valuable each cache is.
@@ -1638,28 +1645,18 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
          *
          * anon in [0], file in [1]
          */
+        spin_lock_irq(&zone->lru_lock);
         if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
-                spin_lock_irq(&zone->lru_lock);
                 reclaim_stat->recent_scanned[0] /= 2;
                 reclaim_stat->recent_rotated[0] /= 2;
-                spin_unlock_irq(&zone->lru_lock);
         }
 
         if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
-                spin_lock_irq(&zone->lru_lock);
                 reclaim_stat->recent_scanned[1] /= 2;
                 reclaim_stat->recent_rotated[1] /= 2;
-                spin_unlock_irq(&zone->lru_lock);
         }
 
         /*
-         * With swappiness at 100, anonymous and file have the same priority.
-         * This scanning priority is essentially the inverse of IO cost.
-         */
-        anon_prio = sc->swappiness;
-        file_prio = 200 - sc->swappiness;
-
-        /*
          * The amount of pressure on anon vs file pages is inversely
          * proportional to the fraction of recently scanned pages on
          * each list that were recently referenced and in active use.
@@ -1669,6 +1666,7 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
 
         fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
         fp /= reclaim_stat->recent_rotated[1] + 1;
+        spin_unlock_irq(&zone->lru_lock);
 
         fraction[0] = ap;
         fraction[1] = fp;