selftests/mm: clarify alternate unmapping in compaction_test

Add a comment explaining that every other entry in the list is unmapped to
intentionally create fragmentation with locked pages before invoking
check_compaction().

Link: https://lore.kernel.org/da5e0a8d5152e54152c0d2f456aac2fac35af291.1779296493.git.sayalip@linux.ibm.com
Fixes: bd67d5c15cc1 ("Test compaction of mlocked memory")
Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/compaction_test.c b/tools/testing/selftests/mm/compaction_test.c
index de0633f9a7e50e4763d1d1364e418af9cba0908a..5b582588e015d412a9e556aad0589411b3691391 100644 (file)
--- 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)