On 15/08/2025 14:54, Usama Arif wrote:

The test will set the global system THP setting to never, madvise
or always depending on the fixture variant and the 2M setting to
inherit before it starts (and reset to original at teardown).
The fixture setup will also test if PR_SET_THP_DISABLE prctl call can
be made to disable all THPs and skip if it fails.

This tests if the process can:
- successfully get the policy to disable THPs completely.
- never get a hugepage when the THPs are completely disabled
  with the prctl, including with MADV_HUGE and MADV_COLLAPSE.
- successfully reset the policy of the process.
- after reset, only get hugepages with:
  - MADV_COLLAPSE when policy is set to never.
  - MADV_HUGE and MADV_COLLAPSE when policy is set to madvise.
  - always when policy is set to "always".
- never get a THP with MADV_NOHUGEPAGE.
- repeat the above tests in a forked process to make sure
  the policy is carried across forks.

Signed-off-by: Usama Arif <redacted>
Acked-by: David Hildenbrand <redacted>
Reviewed-by: Lorenzo Stoakes <redacted>
---
 tools/testing/selftests/mm/.gitignore         |   1 +
 tools/testing/selftests/mm/Makefile           |   1 +
 .../testing/selftests/mm/prctl_thp_disable.c  | 175 ++++++++++++++++++
 tools/testing/selftests/mm/thp_settings.c     |   9 +-
 tools/testing/selftests/mm/thp_settings.h     |   1 +
 5 files changed, 186 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/mm/prctl_thp_disable.c

Andrew, could you please apply the below fixlet on top of this patch as suggested
by David in https://lore.kernel.org/all/a385e09f-f582-4ede-9e60-1d85cee02a3c@redhat.com/ (local)?

Thanks!

From db9306c06cbd6057c2a8839e5d4c1d2559b58b70 Mon Sep 17 00:00:00 2001
From: Usama Arif <redacted>
Date: Mon, 18 Aug 2025 11:27:04 +0100
Subject: [PATCH 2/4] [fixlet] selftests: prctl: return after executing test in
 child process

The next step after executing the test is a wait, but there is nothing to wait
for in the child, so just return.

Signed-off-by: Usama Arif <redacted>
---
 tools/testing/selftests/mm/prctl_thp_disable.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/prctl_thp_disable.c b/tools/testing/selftests/mm/prctl_thp_disable.c
index e9e519c85224c..df3cce278e10a 100644
--- a/tools/testing/selftests/mm/prctl_thp_disable.c
+++ b/tools/testing/selftests/mm/prctl_thp_disable.c

@@ -161,8 +161,10 @@ TEST_F(prctl_thp_disable_completely, fork)
 	pid = fork();
 	ASSERT_GE(pid, 0);
 
-	if (!pid)
+	if (!pid) {
 		prctl_thp_disable_completely_test(_metadata, self->pmdsize, variant->thp_policy);
+		return;
+	}
 
 	wait(&ret);
 	if (WIFEXITED(ret))

-- 
2.47.3