mm, compaction: finish scanning the current pageblock if requested

cc->finish_pageblock is set when the current pageblock should be rescanned
but fast_find_migrateblock can select an alternative block.  Disable
fast_find_migrateblock when the current pageblock scan should be
completed.

Link: https://lkml.kernel.org/r/20230125134434.18017-4-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Chuyi Zhou <zhouchuyi@bytedance.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/compaction.c

@@ -1761,6 +1761,13 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
 	if (cc->ignore_skip_hint)
 		return pfn;
 
+	/*
+	 * If the pageblock should be finished then do not select a different
+	 * pageblock.
+	 */
+	if (cc->finish_pageblock)
+		return pfn;
+
 	/*
 	 * If the migrate_pfn is not at the start of a zone or the start
 	 * of a pageblock then assume this is a continuation of a previous