mm: revert "vmscan: get_scan_ratio() cleanup"

Shaohua Li reported his tmpfs streaming I/O test can lead to make oom.
The test uses a 6G tmpfs in a system with 3G memory.  In the tmpfs, there
are 6 copies of kernel source and the test does kbuild for each copy.  His
investigation shows the test has a lot of rotated anon pages and quite few
file pages, so get_scan_ratio calculates percent[0] (i.e.  scanning
percent for anon) to be zero.  Actually the percent[0] shoule be a big
value, but our calculation round it to zero.

Although before commit 84b18490 ("vmscan: get_scan_ratio() cleanup") , we
have the same problem too.  But the old logic can rescue percent[0]==0
case only when priority==0.  It had hided the real issue.  I didn't think
merely streaming io can makes percent[0]==0 && priority==0 situation.  but
I was wrong.

So, definitely we have to fix such tmpfs streaming io issue.  but anyway I
revert the regression commit at first.

This reverts commit 84b18490d1f1bc7ed5095c929f78bc002eb70f26.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reported-by: Shaohua Li <shaohua.li@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: 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, 14 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index e0e5f15bb726..3ff3311447f5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1535,13 +1535,6 @@ static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
         unsigned long ap, fp;
         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
 
-        /* If we have no swap space, do not bother scanning anon pages. */
-        if (!sc->may_swap || (nr_swap_pages <= 0)) {
-                percent[0] = 0;
-                percent[1] = 100;
-                return;
-        }
-
         anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
         file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
@@ -1639,20 +1632,22 @@ static void shrink_zone(int priority, struct zone *zone,
         unsigned long nr_reclaimed = sc->nr_reclaimed;
         unsigned long nr_to_reclaim = sc->nr_to_reclaim;
         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
+        int noswap = 0;
 
-        get_scan_ratio(zone, sc, percent);
+        /* If we have no swap space, do not bother scanning anon pages. */
+        if (!sc->may_swap || (nr_swap_pages <= 0)) {
+                noswap = 1;
+                percent[0] = 0;
+                percent[1] = 100;
+        } else
+                get_scan_ratio(zone, sc, percent);
 
         for_each_evictable_lru(l) {
                 int file = is_file_lru(l);
                 unsigned long scan;
 
-                if (percent[file] == 0) {
-                        nr[l] = 0;
-                        continue;
-                }
-
                 scan = zone_nr_lru_pages(zone, sc, l);
-                if (priority) {
+                if (priority || noswap) {
                         scan >>= priority;
                         scan = (scan * percent[file]) / 100;
                 }