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Date:   Mon, 4 Feb 2019 08:55:13 +0000
From:   Mel Gorman <mgorman@techsingularity.net>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Vlastimil Babka <vbabka@suse.cz>,
        David Rientjes <rientjes@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
Subject: [PATCH] mm, compaction: Use free lists to quickly locate a migration
 source -fix
Message-ID: <20190204085513.GK9565@techsingularity.net>
References: <20190118175136.31341-1-mgorman@techsingularity.net>
 <20190118175136.31341-10-mgorman@techsingularity.net>
 <4a6ae9fc-a52b-4300-0edb-a0f4169c314a@suse.cz>
 <20190201150614.GJ9565@techsingularity.net>
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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@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;
 }