[PATCH v2 3/4] mm: try to exhaust highatomic reserve before the OOM

[Minchan Kim <minchan@kernel.org>]

It's weird to show that zone has enough free memory above min
watermark but OOMed with 4K GFP_KERNEL allocation due to
reserved highatomic pages. As last resort, try to unreserve
highatomic pages again and if it has moved pages to
non-highatmoc free list, retry reclaim once more.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/page_alloc.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 18808f392718..a7472426663f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2080,7 +2080,7 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
  * intense memory pressure but failed atomic allocations should be easier
  * to recover from than an OOM.
  */
-static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
+static bool unreserve_highatomic_pageblock(const struct alloc_context *ac)
 {
 	struct zonelist *zonelist = ac->zonelist;
 	unsigned long flags;
@@ -2088,6 +2088,7 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
 	struct zone *zone;
 	struct page *page;
 	int order;
+	bool ret = false;
 
 	for_each_zone_zonelist_nodemask(zone, z, zonelist, ac->high_zoneidx,
 								ac->nodemask) {
@@ -2136,12 +2137,14 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
 			 * may increase.
 			 */
 			set_pageblock_migratetype(page, ac->migratetype);
-			move_freepages_block(zone, page, ac->migratetype);
+			ret = move_freepages_block(zone, page, ac->migratetype);
 			spin_unlock_irqrestore(&zone->lock, flags);
-			return;
+			return ret;
 		}
 		spin_unlock_irqrestore(&zone->lock, flags);
 	}
+
+	return ret;
 }
 
 /* Remove an element from the buddy allocator from the fallback list */
@@ -3457,8 +3460,12 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
 	 * Make sure we converge to OOM if we cannot make any progress
 	 * several times in the row.
 	 */
-	if (*no_progress_loops > MAX_RECLAIM_RETRIES)
+	if (*no_progress_loops > MAX_RECLAIM_RETRIES) {
+		/* Before OOM, exhaust highatomic_reserve */
+		if (unreserve_highatomic_pageblock(ac))
+			return true;
 		return false;
+	}
 
 	/*
 	 * Keep reclaiming pages while there is a chance this will lead
-- 
2.7.4

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