mm: vmscan: check if reclaim should really abort even if compaction_ready() is true...

If compaction can proceed for a given zone, shrink_zones() does not
reclaim any more pages from it.  After commit [e0c2327: vmscan: abort
reclaim/compaction if compaction can proceed], do_try_to_free_pages()
tries to finish as soon as possible once one zone can compact.

This was intended to prevent slabs being shrunk unnecessarily but there
are side-effects.  One is that a small zone that is ready for compaction
will abort reclaim even if the chances of successfully allocating a THP
from that zone is small.  It also means that reclaim can return too early
even though sc->nr_to_reclaim pages were not reclaimed.

This partially reverts the commit until it is proven that slabs are really
being shrunk unnecessarily but preserves the check to return 1 to avoid
OOM if reclaim was aborted prematurely.

[aarcange@redhat.com: This patch replaces a revert from Andrea]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Andy Isaacson <adi@hexapodia.org>
Cc: Nai Xia <nai.xia@gmail.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3b8ede8823963653308e38eca5a669a59d28f439..25f90383b3919f1295be6ff45dcc2c0a96bfd1f2 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2217,7 +2217,8 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
  *
  * This function returns true if a zone is being reclaimed for a costly
  * high-order allocation and compaction is ready to begin. This indicates to
- * the caller that it should retry the allocation or fail.
+ * the caller that it should consider retrying the allocation instead of
+ * further reclaim.
  */
 static bool shrink_zones(int priority, struct zonelist *zonelist,
                                        struct scan_control *sc)
@@ -2226,7 +2227,7 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
        struct zone *zone;
        unsigned long nr_soft_reclaimed;
        unsigned long nr_soft_scanned;
-       bool should_abort_reclaim = false;
+       bool aborted_reclaim = false;
 
        for_each_zone_zonelist_nodemask(zone, z, zonelist,
                                        gfp_zone(sc->gfp_mask), sc->nodemask) {
@@ -2252,7 +2253,7 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
                                 * allocations.
                                 */
                                if (compaction_ready(zone, sc)) {
-                                       should_abort_reclaim = true;
+                                       aborted_reclaim = true;
                                        continue;
                                }
                        }
@@ -2274,7 +2275,7 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
                shrink_zone(priority, zone, sc);
        }
 
-       return should_abort_reclaim;
+       return aborted_reclaim;
 }
 
 static bool zone_reclaimable(struct zone *zone)
@@ -2328,7 +2329,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
        struct zoneref *z;
        struct zone *zone;
        unsigned long writeback_threshold;
-       bool should_abort_reclaim;
+       bool aborted_reclaim;
 
        get_mems_allowed();
        delayacct_freepages_start();
@@ -2340,9 +2341,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
                sc->nr_scanned = 0;
                if (!priority)
                        disable_swap_token(sc->target_mem_cgroup);
-               should_abort_reclaim = shrink_zones(priority, zonelist, sc);
-               if (should_abort_reclaim)
-                       break;
+               aborted_reclaim = shrink_zones(priority, zonelist, sc);
 
                /*
                 * Don't shrink slabs when reclaiming memory from
@@ -2409,8 +2408,8 @@ out:
        if (oom_killer_disabled)
                return 0;
 
-       /* Aborting reclaim to try compaction? don't OOM, then */
-       if (should_abort_reclaim)
+       /* Aborted reclaim to try compaction? don't OOM, then */
+       if (aborted_reclaim)
                return 1;
 
        /* top priority shrink_zones still had more to do? don't OOM, then */