[v1,1/3] selftests/mm: Fix half_ufd_size_MB calculation

$half_ufd_size_MB is supposed to be half of the available hugetlb memory
expressed in MB. But previously it was calculated in pages since
$freepgs is the number of free pages.

When huge pages are 2M it doesn't make a whole lot of difference; the
number of pages that get used is just halved. But on arm64 with 16K or
64K base pages, the PMD size (and default hugetlb size) is 32M and 512M
respectively. So in this case we end up passing a number of MB that is
smaller than a single hugetlb page and the test raises an error.

Fixes: 2e47a445d7b3 ("selftests/mm: run_vmtests.sh: fix hugetlb mem size calculation")
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 tools/testing/selftests/mm/run_vmtests.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--
2.43.0

On Tue, Mar 18, 2025 at 05:43:40PM +0000, Ryan Roberts wrote:
> uffd-unit-tests uses a memory area with a fixed 32M size. Then it
> calculates the number of pages by dividing by page_size, which itself is
> either the base page size or the PMD huge page size depending on the
> test config. For the latter, we end up with nr_pages=1 for arm64 16K
> base pages, and nr_pages=0 for 64K base pages. This doesn't end well.
> 
> So let's make the 32M size a floor and also ensure that we have at least
> 2 pages given the PMD size. With this change, the tests pass on arm64
> 64K base page size configuration.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Acked-by: Peter Xu <peterx@redhat.com>

On Tue, Mar 18, 2025 at 05:43:40PM +0000, Ryan Roberts wrote:
> uffd-unit-tests uses a memory area with a fixed 32M size. Then it
> calculates the number of pages by dividing by page_size, which itself is
> either the base page size or the PMD huge page size depending on the
> test config. For the latter, we end up with nr_pages=1 for arm64 16K
> base pages, and nr_pages=0 for 64K base pages. This doesn't end well.
> 
> So let's make the 32M size a floor and also ensure that we have at least
> 2 pages given the PMD size. With this change, the tests pass on arm64
> 64K base page size configuration.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>  tools/testing/selftests/mm/uffd-unit-tests.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index 74c8bc02b506..6973e57b227a 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -26,6 +26,8 @@
>  #define ALIGN_UP(x, align_to) \
>  	((__typeof__(x))((((unsigned long)(x)) + ((align_to)-1)) & ~((align_to)-1)))
>  
> +#define MAX(a, b) (((a) > (b)) ? (a) : (b))
> +
>  struct mem_type {
>  	const char *name;
>  	unsigned int mem_flag;
> @@ -196,7 +198,8 @@ uffd_setup_environment(uffd_test_args_t *args, uffd_test_case_t *test,
>  	else
>  		page_size = psize();
>  
> -	nr_pages = UFFD_TEST_MEM_SIZE / page_size;
> +	/* Ensure we have at least 2 pages */
> +	nr_pages = MAX(UFFD_TEST_MEM_SIZE, page_size * 2) / page_size;
>  	/* TODO: remove this global var.. it's so ugly */
>  	nr_cpus = 1;
>  
> -- 
> 2.43.0
> 
 
Acked-by: Rafael Aquini <raquini@redhat.com>

On 18/03/2025 19:54, Peter Xu wrote:
> On Tue, Mar 18, 2025 at 05:43:39PM +0000, Ryan Roberts wrote:
>> $half_ufd_size_MB is supposed to be half of the available hugetlb memory
>> expressed in MB. But previously it was calculated in pages since
>> $freepgs is the number of free pages.
>>
>> When huge pages are 2M it doesn't make a whole lot of difference; the
>> number of pages that get used is just halved. But on arm64 with 16K or
>> 64K base pages, the PMD size (and default hugetlb size) is 32M and 512M
>> respectively. So in this case we end up passing a number of MB that is
>> smaller than a single hugetlb page and the test raises an error.
>>
>> Fixes: 2e47a445d7b3 ("selftests/mm: run_vmtests.sh: fix hugetlb mem size calculation")
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> 
> There's a similar fix already in akpm/mm-hotfixes-stable:
> 
> 67a2f86846f2 selftests/mm: run_vmtests.sh: fix half_ufd_size_MB calculation

Oops, my bad, forgot to check mm branches. This was just a drive-by fix while
working in another context.

Hopefully Andrew is ok to take the other 2 patches and drop this one? If not,
let me know and I'll resend the two other patches on their own.

Thanks,
Ryan

> 
> Thanks,
> 
>> ---
>>  tools/testing/selftests/mm/run_vmtests.sh | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
>> index da7e26668103..14fa9d40d574 100755
>> --- a/tools/testing/selftests/mm/run_vmtests.sh
>> +++ b/tools/testing/selftests/mm/run_vmtests.sh
>> @@ -304,7 +304,7 @@ uffd_stress_bin=./uffd-stress
>>  CATEGORY="userfaultfd" run_test ${uffd_stress_bin} anon 20 16
>>  # Hugetlb tests require source and destination huge pages. Pass in half
>>  # the size of the free pages we have, which is used for *each*.
>> -half_ufd_size_MB=$((freepgs / 2))
>> +half_ufd_size_MB=$(((freepgs * hpgsize_KB / 2) / 1024))
>>  CATEGORY="userfaultfd" run_test ${uffd_stress_bin} hugetlb "$half_ufd_size_MB" 32
>>  CATEGORY="userfaultfd" run_test ${uffd_stress_bin} hugetlb-private "$half_ufd_size_MB" 32
>>  CATEGORY="userfaultfd" run_test ${uffd_stress_bin} shmem 20 16
>> --
>> 2.43.0
>>
>