mm, compaction: add the ultimate direct compaction priority

During reclaim/compaction loop, it's desirable to get a final answer
from unsuccessful compaction so we can either fail the allocation or
invoke the OOM killer.  However, heuristics such as deferred compaction
or pageblock skip bits can cause compaction to skip parts or whole zones
and lead to premature OOM's, failures or excessive reclaim/compaction
retries.

To remedy this, we introduce a new direct compaction priority called
COMPACT_PRIO_SYNC_FULL, which instructs direct compaction to:

 - ignore deferred compaction status for a zone
 - ignore pageblock skip hints
 - ignore cached scanner positions and scan the whole zone

The new priority should get eventually picked up by
should_compact_retry() and this should improve success rates for costly
allocations using __GFP_REPEAT, such as hugetlbfs allocations, and
reduce some corner-case OOM's for non-costly allocations.

Link: http://lkml.kernel.org/r/20160810091226.6709-6-vbabka@suse.cz
[vbabka@suse.cz: use the MIN_COMPACT_PRIORITY alias]
Link: http://lkml.kernel.org/r/d443b884-87e7-1c93-8684-3a3a35759fb1@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index e88c037afe47bad99854880bbf6e406817907c08..a1fba999472812d0240d5cef58bbed9e0e1d475e 100644 (file)
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -6,8 +6,9 @@
  * Lower value means higher priority, analogically to reclaim priority.
  */
 enum compact_priority {
+       COMPACT_PRIO_SYNC_FULL,
+       MIN_COMPACT_PRIORITY = COMPACT_PRIO_SYNC_FULL,
        COMPACT_PRIO_SYNC_LIGHT,
-       MIN_COMPACT_PRIORITY = COMPACT_PRIO_SYNC_LIGHT,
        DEF_COMPACT_PRIORITY = COMPACT_PRIO_SYNC_LIGHT,
        COMPACT_PRIO_ASYNC,
        INIT_COMPACT_PRIORITY = COMPACT_PRIO_ASYNC

diff --git a/mm/compaction.c b/mm/compaction.c
index 2e1113ff7a0384a52903a3574985fa794a114683..21040304f4d20238a0c2595a9f6b470cb3dbc7ed 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1644,6 +1644,8 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
                .alloc_flags = alloc_flags,
                .classzone_idx = classzone_idx,
                .direct_compaction = true,
+               .whole_zone = (prio == MIN_COMPACT_PRIORITY),
+               .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY)
        };
        INIT_LIST_HEAD(&cc.freepages);
        INIT_LIST_HEAD(&cc.migratepages);
@@ -1689,7 +1691,8 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
                                                                ac->nodemask) {
                enum compact_result status;
 
-               if (compaction_deferred(zone, order)) {
+               if (prio > MIN_COMPACT_PRIORITY
+                                       && compaction_deferred(zone, order)) {
                        rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
                        continue;
                }