Re: [PATCH v3 5/6] selftests: prctl: introduce tests for disabling THPs completely

[David Hildenbrand <david@redhat.com>]

On 04.08.25 17:40, 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).
> 
> This tests if the process can:
> - successfully set and 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".
> - repeat the above tests in a forked process to make sure
>    the policy is carried across forks.
> 
> Signed-off-by: Usama Arif <usamaarif642@gmail.com>
> ---
>   tools/testing/selftests/mm/.gitignore         |   1 +
>   tools/testing/selftests/mm/Makefile           |   1 +
>   .../testing/selftests/mm/prctl_thp_disable.c  | 173 ++++++++++++++++++
>   tools/testing/selftests/mm/thp_settings.c     |   9 +-
>   tools/testing/selftests/mm/thp_settings.h     |   1 +
>   5 files changed, 184 insertions(+), 1 deletion(-)
>   create mode 100644 tools/testing/selftests/mm/prctl_thp_disable.c
> 
> diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
> index e7b23a8a05fe..eb023ea857b3 100644
> --- a/tools/testing/selftests/mm/.gitignore
> +++ b/tools/testing/selftests/mm/.gitignore
> @@ -58,3 +58,4 @@ pkey_sighandler_tests_32
>   pkey_sighandler_tests_64
>   guard-regions
>   merge
> +prctl_thp_disable
> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> index d13b3cef2a2b..2bb8d3ebc17c 100644
> --- a/tools/testing/selftests/mm/Makefile
> +++ b/tools/testing/selftests/mm/Makefile
> @@ -86,6 +86,7 @@ TEST_GEN_FILES += on-fault-limit
>   TEST_GEN_FILES += pagemap_ioctl
>   TEST_GEN_FILES += pfnmap
>   TEST_GEN_FILES += process_madv
> +TEST_GEN_FILES += prctl_thp_disable
>   TEST_GEN_FILES += thuge-gen
>   TEST_GEN_FILES += transhuge-stress
>   TEST_GEN_FILES += uffd-stress
> diff --git a/tools/testing/selftests/mm/prctl_thp_disable.c b/tools/testing/selftests/mm/prctl_thp_disable.c
> new file mode 100644
> index 000000000000..ef150180daf4
> --- /dev/null
> +++ b/tools/testing/selftests/mm/prctl_thp_disable.c
> @@ -0,0 +1,173 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Basic tests for PR_GET/SET_THP_DISABLE prctl calls
> + *
> + * Author(s): Usama Arif <usamaarif642@gmail.com>
> + */
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/mman.h>
> +#include <sys/prctl.h>
> +#include <sys/wait.h>
> +
> +#include "../kselftest_harness.h"
> +#include "thp_settings.h"
> +#include "vm_util.h"
> +
> +static int sz2ord(size_t size, size_t pagesize)
> +{
> +	return __builtin_ctzll(size / pagesize);
> +}

Note: We have this helper duplicated elsewhere (e.g., cow.c).

See [1] how we're going to clean it up.

Not sure how to resolve this. Probably, which series lands first in 
mm-unstable should clean it up.

I would assume that Donet's series would go in first, such that you can 
just reuse the helper from vm_utils.h

[1] https://lkml.kernel.org/r/20250804090410.of5xwrlker665bdp@master


Nothing else jumped at me

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb