[PATCH] mm, compaction: Use free lists to quickly locate a migration source -fix

[Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>]

Vlastimil correctly pointed out that when a fast search fails and cc->migrate_pfn
is reinitialised to the lowest PFN found that the caller does not use the updated
PFN.

This is a fix for the mmotm patch
mm-compaction-use-free-lists-to-quickly-locate-a-migration-source.patch

Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

diff --git a/mm/compaction.c b/mm/compaction.c
index 92d10eb3d1c7..d249f257da7e 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1238,14 +1238,16 @@ update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
 	cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
 }
 
-static inline void
+static inline unsigned long
 reinit_migrate_pfn(struct compact_control *cc)
 {
 	if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
-		return;
+		return cc->migrate_pfn;
 
 	cc->migrate_pfn = cc->fast_start_pfn;
 	cc->fast_start_pfn = ULONG_MAX;
+
+	return cc->migrate_pfn;
 }
 
 /*
@@ -1361,7 +1363,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
 	 * that had free pages as the basis for starting a linear scan.
 	 */
 	if (pfn == cc->migrate_pfn)
-		reinit_migrate_pfn(cc);
+		pfn = reinit_migrate_pfn(cc);
 
 	return pfn;
 }