mm, compaction: distinguish COMPACT_DEFERRED from COMPACT_SKIPPED

try_to_compact_pages() can currently return COMPACT_SKIPPED even when
the compaction is defered for some zone just because zone DMA is skipped
in 99% of cases due to watermark checks.  This makes COMPACT_DEFERRED
basically unusable for the page allocator as a feedback mechanism.

Make sure we distinguish those two states properly and switch their
ordering in the enum.  This would mean that the COMPACT_SKIPPED will be
returned only when all eligible zones are skipped.

As a result COMPACT_DEFERRED handling for THP in __alloc_pages_slowpath
will be more precise and we would bail out rather than reclaim.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index 455ecd87f48d..b2b94474dd28 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1578,7 +1578,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
         int may_perform_io = gfp_mask & __GFP_IO;
         struct zoneref *z;
         struct zone *zone;
-        enum compact_result rc = COMPACT_DEFERRED;
+        enum compact_result rc = COMPACT_SKIPPED;
         int all_zones_contended = COMPACT_CONTENDED_LOCK; /* init for &= op */
 
         *contended = COMPACT_CONTENDED_NONE;
@@ -1595,8 +1595,10 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
                 enum compact_result status;
                 int zone_contended;
 
-                if (compaction_deferred(zone, order))
+                if (compaction_deferred(zone, order)) {
+                        rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
                         continue;
+                }
 
                 status = compact_zone_order(zone, order, gfp_mask, mode,
                                 &zone_contended, alloc_flags,
@@ -1667,7 +1669,7 @@ break_loop:
          * If at least one zone wasn't deferred or skipped, we report if all
          * zones that were tried were lock contended.
          */
-        if (rc > COMPACT_SKIPPED && all_zones_contended)
+        if (rc > COMPACT_INACTIVE && all_zones_contended)
                 *contended = COMPACT_CONTENDED_LOCK;
 
         return rc;