[PATCH 3/3] compaction accouting fix

[Minchan Kim]

I saw the following accouting of compaction during test of the series.

compact_blocks_moved 251
compact_pages_moved 44

It's very awkward to me although it's possbile because it means we try to compact 251 blocks
but it just migrated 44 pages. As further investigation, I found isolate_migratepages doesn't
isolate any pages but it returns ISOLATE_SUCCESS and then, it just increases compact_blocks_moved
but doesn't increased compact_pages_moved.

This patch makes accouting of compaction works only in case of success of isolation.

CC: Mel Gorman <mgorman@xxxxxxx>
CC: Johannes Weiner <jweiner@xxxxxxxxxx>
CC: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
---
 mm/compaction.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 0e572d1..bb3a209 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -260,6 +260,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
	unsigned long low_pfn, end_pfn;
	unsigned long last_pageblock_nr = 0, pageblock_nr;
	unsigned long nr_scanned = 0, nr_isolated = 0;
+	isolate_migrate_t ret = ISOLATE_NONE;
	struct list_head *migratelist = &cc->migratepages;
	isolate_mode_t mode = ISOLATE_ACTIVE| ISOLATE_INACTIVE |
				ISOLATE_UNEVICTABLE;
@@ -273,7 +274,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
	/* Do not cross the free scanner or scan within a memory hole */
	if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
		cc->migrate_pfn = end_pfn;
-		return ISOLATE_NONE;
+		return ret;
	}

	/*
@@ -370,14 +371,17 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
			break;
	}

-	acct_isolated(zone, cc);
+	if (cc->nr_migratepages > 0) {
+		acct_isolated(zone, cc);
+		ret = ISOLATE_SUCCESS;
+	}

	spin_unlock_irq(&zone->lru_lock);
	cc->migrate_pfn = low_pfn;

	trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);

-	return ISOLATE_SUCCESS;
+	return ret;
 }

 /*
--
1.7.6
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