Re: [PATCH 3/4] selftests/mm: add check_folio_orders() helper.

[Zi Yan <ziy@nvidia.com>]

On 7 Aug 2025, at 2:49, Baolin Wang wrote:

> On 2025/8/6 10:20, Zi Yan wrote:
>> The helper gathers an folio order statistics of folios within a virtual
>> address range and checks it against a given order list. It aims to provide
>> a more precise folio order check instead of just checking the existence of
>> PMD folios.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>>   tools/testing/selftests/mm/vm_util.c | 139 +++++++++++++++++++++++++++
>>   tools/testing/selftests/mm/vm_util.h |   2 +
>>   2 files changed, 141 insertions(+)
>>
>> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
>> index 9dafa7669ef9..373621145b2a 100644
>> --- a/tools/testing/selftests/mm/vm_util.c
>> +++ b/tools/testing/selftests/mm/vm_util.c
>> @@ -17,6 +17,12 @@
>>   #define STATUS_FILE_PATH "/proc/self/status"
>>   #define MAX_LINE_LENGTH 500
>>  +#define PGMAP_PRESENT		(1UL << 63)
>> +#define KPF_COMPOUND_HEAD	(1UL << 15)
>> +#define KPF_COMPOUND_TAIL	(1UL << 16)
>> +#define KPF_THP			(1UL << 22)
>> +#define PFN_MASK     ((1UL<<55)-1)
>> +
>>   unsigned int __page_size;
>>   unsigned int __page_shift;
>>  @@ -338,6 +344,139 @@ int detect_hugetlb_page_sizes(size_t sizes[], int max)
>>   	return count;
>>   }
>>  +static int get_page_flags(uint64_t vpn, int pagemap_file, int kpageflags_file,
>> +			  uint64_t *flags)
>> +{
>> +	uint64_t pfn;
>> +	size_t count;
>> +
>> +	count = pread(pagemap_file, &pfn, sizeof(pfn),
>> +		      vpn * sizeof(pfn));
>> +
>> +	if (count != sizeof(pfn))
>> +		return -1;
>> +
>> +	/*
>> +	 * Treat non-present page as a page without any flag, so that
>> +	 * gather_folio_orders() just record the current folio order.
>> +	 */
>> +	if (!(pfn & PGMAP_PRESENT)) {
>> +		*flags = 0;
>> +		return 0;
>> +	}
>
> It looks like you can reuse the helper pagemap_get_pfn() in this file?

Sure.

>
>> +
>> +	count = pread(kpageflags_file, flags, sizeof(*flags),
>> +		      (pfn & PFN_MASK) * sizeof(*flags));
>> +
>> +	if (count != sizeof(*flags))
>> +		return -1;
>> +
>> +	return 0;
>> +}
>> +
>> +static int gather_folio_orders(uint64_t vpn_start, size_t nr_pages,
>
> In this file, other helper functions use userspace virtual address as parameters, so can we consistently use virtual address for calculations instead of the 'vpn_start'?
>

Sure.

>> +			       int pagemap_file, int kpageflags_file,
>> +			       int orders[], int nr_orders)
>> +{
>> +	uint64_t page_flags = 0;
>> +	int cur_order = -1;
>> +	uint64_t vpn;
>> +
>> +	if (!pagemap_file || !kpageflags_file)
>> +		return -1;
>> +	if (nr_orders <= 0)
>> +		return -1;
>> +
>> +	for (vpn = vpn_start; vpn < vpn_start + nr_pages; ) {
>> +		uint64_t next_folio_vpn;
>> +		int status;
>> +
>> +		if (get_page_flags(vpn, pagemap_file, kpageflags_file, &page_flags))
>> +			return -1;
>> +
>> +		/* all order-0 pages with possible false postive (non folio) */
>> +		if (!(page_flags & (KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))) {
>> +			orders[0]++;
>> +			vpn++;
>> +			continue;
>> +		}
>> +
>> +		/* skip non thp compound pages */
>> +		if (!(page_flags & KPF_THP)) {
>> +			vpn++;
>> +			continue;
>> +		}
>> +
>> +		/* vpn points to part of a THP at this point */
>> +		if (page_flags & KPF_COMPOUND_HEAD)
>> +			cur_order = 1;
>> +		else {
>> +			/* not a head nor a tail in a THP? */
>> +			if (!(page_flags & KPF_COMPOUND_TAIL))
>> +				return -1;
>> +			continue;
>> +		}
>> +
>> +		next_folio_vpn = vpn + (1 << cur_order);
>> +
>> +		if (next_folio_vpn >= vpn_start + nr_pages)
>> +			break;
>> +
>> +		while (!(status = get_page_flags(next_folio_vpn, pagemap_file,
>> +						 kpageflags_file,
>> +						 &page_flags))) {
>> +			/* next compound head page or order-0 page */
>> +			if ((page_flags & KPF_COMPOUND_HEAD) ||
>> +			    !(page_flags & (KPF_COMPOUND_HEAD |
>> +			      KPF_COMPOUND_TAIL))) {
>> +				if (cur_order < nr_orders) {
>> +					orders[cur_order]++;
>> +					cur_order = -1;
>> +					vpn = next_folio_vpn;
>> +				}
>> +				break;
>> +			}
>> +
>> +			/* not a head nor a tail in a THP? */
>> +			if (!(page_flags & KPF_COMPOUND_TAIL))
>> +				return -1;
>> +
>> +			cur_order++;
>> +			next_folio_vpn = vpn + (1 << cur_order);
>> +		}
>> +
>> +		if (status)
>> +			return status;
>> +	}
>> +	if (cur_order > 0 && cur_order < nr_orders)
>> +		orders[cur_order]++;
>> +	return 0;
>> +}
>> +
>> +int check_folio_orders(uint64_t vpn_start, size_t nr_pages, int pagemap_file,
>> +			int kpageflags_file, int orders[], int nr_orders)
>> +{
>> +	int vpn_orders[nr_orders];
>
> IIRC, we should avoid using VLA (variable length arrays)?

OK. I can change it to malloc.

Thanks.

>
>> +	int status;
>> +	int i;
>> +
>> +	memset(vpn_orders, 0, sizeof(int) * nr_orders);
>> +	status = gather_folio_orders(vpn_start, nr_pages, pagemap_file,
>> +				     kpageflags_file, vpn_orders, nr_orders);
>> +	if (status)
>> +		return status;
>> +
>> +	status = 0;
>> +	for (i = 0; i < nr_orders; i++)
>> +		if (vpn_orders[i] != orders[i]) {
>> +			ksft_print_msg("order %d: expected: %d got %d\n", i,
>> +				       orders[i], vpn_orders[i]);
>> +			status = -1;
>> +		}
>> +
>> +	return status;
>> +}
>> +
>>   /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
>>   int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
>>   			      bool miss, bool wp, bool minor, uint64_t *ioctls)
>> diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
>> index b55d1809debc..dee9504a6129 100644
>> --- a/tools/testing/selftests/mm/vm_util.h
>> +++ b/tools/testing/selftests/mm/vm_util.h
>> @@ -85,6 +85,8 @@ bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size);
>>   int64_t allocate_transhuge(void *ptr, int pagemap_fd);
>>   unsigned long default_huge_page_size(void);
>>   int detect_hugetlb_page_sizes(size_t sizes[], int max);
>> +int check_folio_orders(uint64_t vpn_start, size_t nr_pages, int pagemap_file,
>> +			int kpageflags_file, int orders[], int nr_orders);
>>    int uffd_register(int uffd, void *addr, uint64_t len,
>>   		  bool miss, bool wp, bool minor);


--
Best Regards,
Yan, Zi