[PATCHv2] mm/compaction: reset compaction scanner positions

[Gioh Kim]

When the compaction is activated via /proc/sys/vm/compact_memory
it would better scan the whole zone.
And some platform, for instance ARM, has the start_pfn of a zone is zero.
Therefore the first try to compaction via /proc doesn't work.
It needs to force to reset compaction scanner position at first.

Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 mm/compaction.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/compaction.c b/mm/compaction.c
index 8c0d945..ccf48ce 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1587,6 +1587,14 @@ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
 		INIT_LIST_HEAD(&cc->freepages);
 		INIT_LIST_HEAD(&cc->migratepages);
 
+		/*
+		 * When called via /proc/sys/vm/compact_memory
+		 * this makes sure we compact the whole zone regardless of
+		 * cached scanner positions.
+		 */
+		if (cc->order == -1)
+			__reset_isolation_suitable(zone);
+
 		if (cc->order == -1 || !compaction_deferred(zone, cc->order))
 			compact_zone(zone, cc);
 
-- 
1.7.9.5

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