I'm attaching the patch for discussion.
According to Vlastimil's advice, I move the reseting before compact_zone(),
and write more description.
Vlastimil, can I have your name at Acked-by or Signed-off-by?
Which one do you prefer?
------------------------- 8< ----------------------
From 575983c887e6478ca7cbba49a892dbc4cd69986b Mon Sep 17 00:00:00 2001
From: Gioh Kim <gioh....@lge.com>
Date: Fri, 20 Mar 2015 21:09:13 +0900
Subject: [PATCH] [RFCv2] mm/compaction: reset compaction scanner positions
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 as 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....@lge.com>
---
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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