[PATCH 5.9 210/255] mm/compaction: stop isolation if too many pages are isolated and we have pages to migrate

[Greg Kroah-Hartman]

From: Zi Yan <ziy@xxxxxxxxxx>

commit d20bdd571ee5c9966191568527ecdb1bd4b52368 upstream.

In isolate_migratepages_block, if we have too many isolated pages and
nr_migratepages is not zero, we should try to migrate what we have
without wasting time on isolating.

In theory it's possible that multiple parallel compactions will cause
too_many_isolated() to become true even if each has isolated less than
COMPACT_CLUSTER_MAX, and loop forever in the while loop.  Bailing
immediately prevents that.

[vbabka@xxxxxxx: changelog addition]

Fixes: 1da2f328fa64 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”)
Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20201030183809.3616803-2-zi.yan@xxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/compaction.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -818,6 +818,10 @@ isolate_migratepages_block(struct compac
 	 * delay for some time until fewer pages are isolated
 	 */
 	while (unlikely(too_many_isolated(pgdat))) {
+		/* stop isolation if there are still pages not migrated */
+		if (cc->nr_migratepages)
+			return 0;
+
 		/* async migration should just abort */
 		if (cc->mode == MIGRATE_ASYNC)
 			return 0;