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[PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders

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The __compaction_suitable() function checks the low watermark plus a
compact_gap() gap to decide if there's enough free memory to perform
compaction. Then __isolate_free_page uses low watermark check to decide if
particular free page can be isolated. In the latter case, using low watermark
is needlessly pessimistic, as the free page isolations are only temporary. For
__compaction_suitable() the higher watermark makes sense for high-order
allocations where more freepages increase the chance of success, and we can
typically fail with some order-0 fallback when the system is struggling to
reach that watermark. But for low-order allocation, forming the page should not
be that hard. So using low watermark here might just prevent compaction from
even trying, and eventually lead to OOM killer even if we are above min
watermarks.

So after this patch, we use min watermark for non-costly orders in
__compaction_suitable(), and for all orders in __isolate_free_page().

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 mm/compaction.c | 6 +++++-
 mm/page_alloc.c | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 80eaf9fff114..0bba270f97ad 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1399,10 +1399,14 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
 	 * isolation. We however do use the direct compactor's classzone_idx to
 	 * skip over zones where lowmem reserves would prevent allocation even
 	 * if compaction succeeds.
+	 * For costly orders, we require low watermark instead of min for
+	 * compaction to proceed to increase its chances.
 	 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
 	 * suitable migration targets
 	 */
-	watermark = low_wmark_pages(zone) + compact_gap(order);
+	watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
+				low_wmark_pages(zone) : min_wmark_pages(zone);
+	watermark += compact_gap(order);
 	if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
 						ALLOC_CMA, wmark_target))
 		return COMPACT_SKIPPED;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 621e4211ce16..a5c0f914ec00 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2492,7 +2492,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
 
 	if (!is_migrate_isolate(mt)) {
 		/* Obey watermarks as if the page was being allocated */
-		watermark = low_wmark_pages(zone) + (1 << order);
+		watermark = min_wmark_pages(zone) + (1UL << order);
 		if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
 			return 0;
 
-- 
2.9.2

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[PATCH v6 00/11] make direct compaction more deterministic Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 20:20 +0200
  [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
    Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct  compaction priority Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:10 +0200
      Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct  compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-16 08:40 +0200
    Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct  compaction priority Michal Hocko <mhocko@kernel.org> - 2016-08-18 11:20 +0200
      Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct  compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 11:50 +0200
        Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct  compaction priority Michal Hocko <mhocko@kernel.org> - 2016-08-18 12:00 +0200
  [PATCH v6 09/11] mm, compaction: use proper alloc_flags in __compaction_suitable() Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
  [PATCH v6 01/11] mm, compaction: make whole_zone flag ignore cached scanner positions Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
  [PATCH v6 07/11] mm, compaction: use correct watermark when checking compaction success Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
  [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
    Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Vlastimil Babka <vbabka@suse.cz> - 2016-08-16 08:20 +0200
      Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:40 +0200
        Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 14:20 +0200
    Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:20 +0200
  [PATCH v6 03/11] mm, compaction: rename COMPACT_PARTIAL to COMPACT_SUCCESS Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
    Re: [PATCH v6 03/11] mm, compaction: rename COMPACT_PARTIAL to  COMPACT_SUCCESS Michal Hocko <mhocko@kernel.org> - 2016-08-18 13:10 +0200
  [PATCH v6 02/11] mm, compaction: cleanup unused functions Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
  [PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
    Re: [PATCH v6 10/11] mm, compaction: require only min watermarks for  non-costly orders Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:20 +0200
      Re: [PATCH v6 10/11] mm, compaction: require only min watermarks for  non-costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-08-16 08:40 +0200
        Re: [PATCH v6 10/11] mm, compaction: require only min watermarks for  non-costly orders Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:50 +0200
          Re: [PATCH v6 10/11] mm, compaction: require only min watermarks for  non-costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 14:30 +0200
  [PATCH v6 05/11] mm, compaction: add the ultimate direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
    Re: [PATCH v6 05/11] mm, compaction: add the ultimate direct  compaction priority Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:00 +0200
      Re: [PATCH v6 05/11] mm, compaction: add the ultimate direct  compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 14:30 +0200
  [PATCH v6 11/11] mm, vmscan: make compaction_ready() more accurate and readable Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
  [PATCH v6 04/11] mm, compaction: don't recheck watermarks after COMPACT_SUCCESS Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
    Re: [PATCH v6 04/11] mm, compaction: don't recheck watermarks after  COMPACT_SUCCESS Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:10 +0200
      Re: [PATCH v6 04/11] mm, compaction: don't recheck watermarks after  COMPACT_SUCCESS Vlastimil Babka <vbabka@suse.cz> - 2016-08-16 08:20 +0200
      Re: [PATCH v6 04/11] mm, compaction: don't recheck watermarks after  COMPACT_SUCCESS Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 14:00 +0200
    Re: [PATCH v6 04/11] mm, compaction: don't recheck watermarks after  COMPACT_SUCCESS Michal Hocko <mhocko@kernel.org> - 2016-08-18 11:10 +0200

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