[PATCH v2 1/4] mm, reclaim: make should_continue_reclaim perform dryrun detection

[Mike Kravetz]

From: Hillf Danton <hdanton@xxxxxxxx>

Address the issue of should_continue_reclaim returning true too often
for __GFP_RETRY_MAYFAIL attempts when !nr_reclaimed and nr_scanned.
This was observed during hugetlb page allocation causing stalls for
minutes or hours.

We can stop reclaiming pages if compaction reports it can make a progress.
There might be side-effects for other high-order allocations that would
potentially benefit from reclaiming more before compaction so that they
would be faster and less likely to stall.  However, the consequences of
premature/over-reclaim are considered worse.

We can also bail out of reclaiming pages if we know that there are not
enough inactive lru pages left to satisfy the costly allocation.

We can give up reclaiming pages too if we see dryrun occur, with the
certainty of plenty of inactive pages. IOW with dryrun detected, we are
sure we have reclaimed as many pages as we could.

Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Hillf Danton <hdanton@xxxxxxxx>
Tested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
v2 - Updated commit message and added SOB.

 mm/vmscan.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 47aa2158cfac..a386c5351592 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2738,18 +2738,6 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
 			return false;
 	}
 
-	/*
-	 * If we have not reclaimed enough pages for compaction and the
-	 * inactive lists are large enough, continue reclaiming
-	 */
-	pages_for_compaction = compact_gap(sc->order);
-	inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
-	if (get_nr_swap_pages() > 0)
-		inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
-	if (sc->nr_reclaimed < pages_for_compaction &&
-			inactive_lru_pages > pages_for_compaction)
-		return true;
-
 	/* If compaction would go ahead or the allocation would succeed, stop */
 	for (z = 0; z <= sc->reclaim_idx; z++) {
 		struct zone *zone = &pgdat->node_zones[z];
@@ -2765,7 +2753,21 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
 			;
 		}
 	}
-	return true;
+
+	/*
+	 * If we have not reclaimed enough pages for compaction and the
+	 * inactive lists are large enough, continue reclaiming
+	 */
+	pages_for_compaction = compact_gap(sc->order);
+	inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
+	if (get_nr_swap_pages() > 0)
+		inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
+
+	return inactive_lru_pages > pages_for_compaction &&
+		/*
+		 * avoid dryrun with plenty of inactive pages
+		 */
+		nr_scanned && nr_reclaimed;
 }
 
 static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
-- 
2.20.1