[PATCH] mm, compaction: prevent endless loop in migrate scanner

[Vlastimil Babka]

---
 mm/compaction.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index ec74cf0..1b7a1be 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1029,8 +1029,12 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 	}
 
 	acct_isolated(zone, cc);
-	/* Record where migration scanner will be restarted */
-	cc->migrate_pfn = low_pfn;
+	/* 
+	 * Record where migration scanner will be restarted. If we end up in
+	 * the same pageblock as the free scanner, make the scanners fully
+	 * meet so that compact_finished() terminates compaction.
+	 */
+	cc->migrate_pfn = (end_pfn <= cc->free_pfn) ? low_pfn : cc->free_pfn;
 
 	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
 }
-- 
2.1.2


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