vmscan: check high watermark after shrink zone

Kswapd checks that zone has sufficient pages free via zone_watermark_ok().

If any zone doesn't have enough pages, we set all_zones_ok to zero.
!all_zone_ok makes kswapd retry rather than sleeping.

I think the watermark check before shrink_zone() is pointless.  Only after
kswapd has tried to shrink the zone is the check meaningful.

Move the check to after the call to shrink_zone().

[akpm@linux-foundation.org: fix comment, layout]
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 10 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c26986c85ce0..96ebe6608d5c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2060,9 +2060,6 @@ loop_again:
                                         priority != DEF_PRIORITY)
                                 continue;
 
-                        if (!zone_watermark_ok(zone, order,
-                                        high_wmark_pages(zone), end_zone, 0))
-                                all_zones_ok = 0;
                         temp_priority[i] = priority;
                         sc.nr_scanned = 0;
                         note_zone_scanning_priority(zone, priority);
@@ -2102,13 +2099,18 @@ loop_again:
                             total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
                                 sc.may_writepage = 1;
 
-                        /*
-                         * We are still under min water mark. it mean we have
-                         * GFP_ATOMIC allocation failure risk. Hurry up!
-                         */
-                        if (!zone_watermark_ok(zone, order, min_wmark_pages(zone),
-                                              end_zone, 0))
-                                has_under_min_watermark_zone = 1;
+                        if (!zone_watermark_ok(zone, order,
+                                        high_wmark_pages(zone), end_zone, 0)) {
+                                all_zones_ok = 0;
+                                /*
+                                 * We are still under min water mark.  This
+                                 * means that we have a GFP_ATOMIC allocation
+                                 * failure risk. Hurry up!
+                                 */
+                                if (!zone_watermark_ok(zone, order,
+                                            min_wmark_pages(zone), end_zone, 0))
+                                        has_under_min_watermark_zone = 1;
+                        }
 
                 }
                 if (all_zones_ok)