diff --git a/tools/testing/selftests/mm/compaction_test.c b/tools/testing/selftests/mm/compaction_test.c
index de0633f9a7e5..5b582588e015 100644
--- a/tools/testing/selftests/mm/compaction_test.c
+++ b/tools/testing/selftests/mm/compaction_test.c
@@ -181,6 +181,9 @@ int main(int argc, char **argv)
 		mem_fragmentable_MB -= MAP_SIZE_MB;
 	}
 
+	/* Unmap every other entry in the list to create fragmentation with
+	 * locked pages before invoking check_compaction().
+	 */
 	for (entry = list; entry != NULL; entry = entry->next) {
 		munmap(entry->map, MAP_SIZE);
 		if (!entry->next)