Re: [PATCH v5 7/7] selftests: prctl: introduce tests for disabling THPs except for madvise

[Usama Arif <usamaarif642@gmail.com>]

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 with PR_THP_DISABLE_EXCEPT_ADVISED and skip if it fails.
> 
> This tests if the process can:
> - successfully get the policy to disable THPs expect for madvise.
> - get hugepages only on MADV_HUGE and MADV_COLLAPSE if the global policy
>   is madvise/always and only with MADV_COLLAPSE if the global policy is
>   never.
> - 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.
> 
> Test results:
> ./prctl_thp_disable
> TAP version 13
> 1..12
> ok 1 prctl_thp_disable_completely.never.nofork
> ok 2 prctl_thp_disable_completely.never.fork
> ok 3 prctl_thp_disable_completely.madvise.nofork
> ok 4 prctl_thp_disable_completely.madvise.fork
> ok 5 prctl_thp_disable_completely.always.nofork
> ok 6 prctl_thp_disable_completely.always.fork
> ok 7 prctl_thp_disable_except_madvise.never.nofork
> ok 8 prctl_thp_disable_except_madvise.never.fork
> ok 9 prctl_thp_disable_except_madvise.madvise.nofork
> ok 10 prctl_thp_disable_except_madvise.madvise.fork
> ok 11 prctl_thp_disable_except_madvise.always.nofork
> ok 12 prctl_thp_disable_except_madvise.always.fork
> 
> Signed-off-by: Usama Arif <usamaarif642@gmail.com>
> ---


Andrew could you please help apply the below fixlet on top of this patch?

Thanks!

From 85908068c15fee0b9e5796fbc552e38239c2765a Mon Sep 17 00:00:00 2001
From: Usama Arif <usamaarif642@gmail.com>
Date: Mon, 18 Aug 2025 11:37:10 +0100
Subject: [PATCH 4/4] [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 <usamaarif642@gmail.com>
---
 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 21d181ab599a2..feb711dca3a1d 100644
--- a/tools/testing/selftests/mm/prctl_thp_disable.c
+++ b/tools/testing/selftests/mm/prctl_thp_disable.c
@@ -273,9 +273,11 @@ TEST_F(prctl_thp_disable_except_madvise, fork)
 	pid = fork();
 	ASSERT_GE(pid, 0);
 
-	if (!pid)
+	if (!pid) {
 		prctl_thp_disable_except_madvise_test(_metadata, self->pmdsize,
 						      variant->thp_policy);
+		return;
+	}
 
 	wait(&ret);
 	if (WIFEXITED(ret))
-- 
2.47.3