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

[Mel Gorman]

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 <mgor...@techsingularity.net>

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;
 }