[PATCH][RFCv2] mm/compaction: reset compaction scanner positions

[Gioh Kim <gioh.kim@lge.com>]

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.kim@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.kim@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