Re: [PATCH v3 49/54] selftests/mm: uffd-unit-tests: add setup of HugeTLB pages

[Sarthak Sharma]

Hi Mike!

On 4/29/26 2:12 AM, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>
> 
> uffd-unit-tests skips HugeTLB tests if there are no free huge pages
> prepared by a wrapper script.
> 
> Add setup of HugeTLB pages to the test and make sure that the original
> settings are restored on the test exit.
> 
> Replace exit() calls with _exit() to avoid restoring HugeTLB settings in
> the middle of test.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> ---
>  tools/testing/selftests/mm/uffd-unit-tests.c | 31 +++++++++++++++++---
>  1 file changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index 1a33db281f8a..20e1829db91f 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -305,7 +305,7 @@ static int pagemap_test_fork(uffd_global_test_opts_t *gopts, bool with_event, bo
>  		if (test_pin)
>  			unpin_pages(&args);
>  		/* Succeed */
> -		exit(0);
> +		_exit(0);
>  	}
>  	waitpid(child, &result, 0);
>  
> @@ -773,7 +773,7 @@ static void uffd_sigbus_test_common(uffd_global_test_opts_t *gopts, bool wp)
>  		err("fork");
>  
>  	if (!pid)
> -		exit(faulting_process(gopts, 2, wp));
> +		_exit(faulting_process(gopts, 2, wp));
>  
>  	waitpid(pid, &err, 0);
>  	if (err)
> @@ -827,7 +827,7 @@ static void uffd_events_test_common(uffd_global_test_opts_t *gopts, bool wp)
>  		err("fork");
>  
>  	if (!pid)
> -		exit(faulting_process(gopts, 0, wp));
> +		_exit(faulting_process(gopts, 0, wp));
>  
>  	waitpid(pid, &err, 0);
>  	if (err)
> @@ -1706,11 +1706,32 @@ static int uffd_count_tests(int n_tests, int n_mems, const char *test_filter)
>  	return count;
>  }
>  
> +static unsigned long uffd_setup_hugetlb(void)
> +{
> +	unsigned long nr_hugepages, hp_size;
> +
> +	hugetlb_save_settings();
> +	hp_size = default_huge_page_size();
> +
> +	if (!hp_size)
> +		return 0;
> +
> +	/* need twice UFFD_TEST_MEM_SIZE, one for src area and one for dst */
> +	nr_hugepages = 2 * MAX(UFFD_TEST_MEM_SIZE, hp_size * 2) / hp_size;
> +	hugetlb_set_nr_default_pages(nr_hugepages);
> +
> +	if (hugetlb_free_default_pages() < nr_hugepages)
> +		return 0;
> +
> +	return hp_size;
> +}
> +
>  int main(int argc, char *argv[])
>  {
>  	int n_tests = sizeof(uffd_tests) / sizeof(uffd_test_case_t);
>  	int n_mems = sizeof(mem_types) / sizeof(mem_type_t);
>  	const char *test_filter = NULL;
> +	unsigned long hugepage_size;
>  	bool list_only = false;
>  	uffd_test_case_t *test;
>  	mem_type_t *mem_type;
> @@ -1745,6 +1766,8 @@ int main(int argc, char *argv[])
>  		return KSFT_PASS;
>  	}
>  
> +	hugepage_size = uffd_setup_hugetlb();
> +
>  	ksft_print_header();
>  	ksft_set_plan(uffd_count_tests(n_tests, n_mems, test_filter));
>  
> @@ -1771,7 +1794,7 @@ int main(int argc, char *argv[])
>  			uffd_test_case_ops = test->test_case_ops;
>  
>  			if (mem_type->mem_flag & (MEM_HUGETLB_PRIVATE | MEM_HUGETLB)) {
> -				gopts.page_size = default_huge_page_size();
> +				gopts.page_size = hugepage_size;
>  				if (gopts.page_size == 0) {
>  					uffd_test_skip("huge page size is 0, feature missing?");

A small nit, after this patch, uffd_setup_hugetlb() can return 0 in 2 cases:

a) default_huge_page_size() == 0
b) hugetlb_free_default_pages() < nr_hugepages

The skip message only covers the first case and would be misleading for
the second case. Should we differentiate both these using different skip
messages?

>  					continue;