On 10/12/2016 07:33 AM, Minchan Kim wrote:
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.


I would move the details (OOM report etc) from the cover letter here, otherwise they end up in Patch 1's changelog, which is less helpful.

Signed-off-by: Michal Hocko <mho...@suse.com>
Signed-off-by: Minchan Kim <minc...@kernel.org>

Acked-by: Vlastimil Babka <vba...@suse.cz>

---
 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


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