vmscan: abort reclaim/compaction if compaction can proceed

If compaction can proceed, shrink_zones() stops doing any work but its
callers still call shrink_slab() which raises the priority and potentially
sleeps.  This is unnecessary and wasteful so this patch aborts direct
reclaim/compaction entirely if compaction can proceed.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Johannes Weiner <jweiner@redhat.com>
Cc: Josh Boyer <jwboyer@redhat.com>
Cc: Andrea Arcangeli <aarcange@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 7e0f0579738889c092d00834519cabe0b552a527..a90c603a8d02937fd41bac6a7e72d2891f86bfaa 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2103,14 +2103,19 @@ restart:
  *
  * If a zone is deemed to be full of pinned pages then just give it a light
  * scan then give up on it.
+ *
+ * This function returns true if a zone is being reclaimed for a costly
+ * high-order allocation and compaction is either ready to begin or deferred.
+ * This indicates to the caller that it should retry the allocation or fail.
  */
-static void shrink_zones(int priority, struct zonelist *zonelist,
+static bool shrink_zones(int priority, struct zonelist *zonelist,
                                        struct scan_control *sc)
 {
        struct zoneref *z;
        struct zone *zone;
        unsigned long nr_soft_reclaimed;
        unsigned long nr_soft_scanned;
+       bool should_abort_reclaim = false;
 
        for_each_zone_zonelist_nodemask(zone, z, zonelist,
                                        gfp_zone(sc->gfp_mask), sc->nodemask) {
@@ -2127,19 +2132,20 @@ static void shrink_zones(int priority, struct zonelist *zonelist,
                                continue;       /* Let kswapd poll it */
                        if (COMPACTION_BUILD) {
                                /*
-                                * If we already have plenty of memory
-                                * free for compaction, don't free any
-                                * more.  Even though compaction is
-                                * invoked for any non-zero order,
-                                * only frequent costly order
-                                * reclamation is disruptive enough to
-                                * become a noticable problem, like
-                                * transparent huge page allocations.
+                                * If we already have plenty of memory free for
+                                * compaction in this zone, don't free any more.
+                                * Even though compaction is invoked for any
+                                * non-zero order, only frequent costly order
+                                * reclamation is disruptive enough to become a
+                                * noticable problem, like transparent huge page
+                                * allocations.
                                 */
                                if (sc->order > PAGE_ALLOC_COSTLY_ORDER &&
                                        (compaction_suitable(zone, sc->order) ||
-                                        compaction_deferred(zone)))
+                                        compaction_deferred(zone))) {
+                                       should_abort_reclaim = true;
                                        continue;
+                               }
                        }
                        /*
                         * This steals pages from memory cgroups over softlimit
@@ -2158,6 +2164,8 @@ static void shrink_zones(int priority, struct zonelist *zonelist,
 
                shrink_zone(priority, zone, sc);
        }
+
+       return should_abort_reclaim;
 }
 
 static bool zone_reclaimable(struct zone *zone)
@@ -2222,7 +2230,9 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
                sc->nr_scanned = 0;
                if (!priority)
                        disable_swap_token(sc->mem_cgroup);
-               shrink_zones(priority, zonelist, sc);
+               if (shrink_zones(priority, zonelist, sc))
+                       break;
+
                /*
                 * Don't shrink slabs when reclaiming memory from
                 * over limit cgroups