Re: [PATCH v3 2/4] selftests/mm: add check_folio_orders() helper.

[Zi Yan <ziy@nvidia.com>]

On 12 Aug 2025, at 23:38, wang lian wrote:

>> On Aug 12, 2025, at 23:55, Zi Yan <ziy@nvidia.com> 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>
>> ---
>> .../selftests/mm/split_huge_page_test.c       |   4 +-
>> tools/testing/selftests/mm/vm_util.c          | 173 ++++++++++++++++++
>> tools/testing/selftests/mm/vm_util.h          |   7 +
>> 3 files changed, 181 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>> index 5d07b0b89226..63ac82f0b9e0 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -34,8 +34,6 @@ uint64_t pmd_pagesize;
>> #define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
>> #define PATH_FMT "%s,0x%lx,0x%lx,%d"
>>
>> -#define PFN_MASK     ((1UL<<55)-1)
>> -#define KPF_THP      (1UL<<22)
>> #define GET_ORDER(nr_pages)    (31 - __builtin_clz(nr_pages))
>>
>> int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>> @@ -49,7 +47,7 @@ int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>>
>> 		if (kpageflags_file) {
>> 			pread(kpageflags_file, &page_flags, sizeof(page_flags),
>> -				(paddr & PFN_MASK) * sizeof(page_flags));
>> +				PAGEMAP_PFN(paddr) * sizeof(page_flags));
>>
>> 			return !!(page_flags & KPF_THP);
>> 		}
>> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
>> index 6a239aa413e2..4d952d1bc96d 100644
>> --- a/tools/testing/selftests/mm/vm_util.c
>> +++ b/tools/testing/selftests/mm/vm_util.c
>> @@ -338,6 +338,179 @@ int detect_hugetlb_page_sizes(size_t sizes[], int max)
>> 	return count;
>> }
>>
>> +static int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
>> +{
>> +	size_t count;
>> +
>> +	count = pread(kpageflags_fd, flags, sizeof(*flags),
>> +		      pfn * sizeof(*flags));
>> +
>> +	if (count != sizeof(*flags))
>> +		return -1;
>> +
>> +	return 0;
>> +}
>> +
>> +static int get_page_flags(char *vaddr, int pagemap_fd, int kpageflags_fd,
>> +			  uint64_t *flags)
>> +{
>> +	unsigned long pfn;
>> +
>> +	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
>> +	/*
>> +	 * Treat non-present page as a page without any flag, so that
>> +	 * gather_folio_orders() just record the current folio order.
>> +	 */
>> +	if (pfn == -1UL) {
>> +		*flags = 0;
>> +		return 1;
>> +	}
>> +
>> +	if (get_pfn_flags(pfn, kpageflags_fd, flags))
>> +		return -1;
>> +
>> +	return 0;
>> +}
>> +
>> +/*
>> + * gather_folio_orders - scan through [vaddr_start, len) and record folio orders
>> + * @vaddr_start: start vaddr
>> + * @len: range length
>> + * @pagemap_fd: file descriptor to /proc/<pid>/pagemap
>> + * @kpageflags_fd: file descriptor to /proc/kpageflags
>> + * @orders: output folio order array
>> + * @nr_orders: folio order array size
>> + *
>> + * gather_folio_orders() scan through [vaddr_start, len) and check all folios
>> + * within the range and record their orders. All order-0 pages will be recorded.
>> + * Non-present vaddr is skipped.
>> + *
>> + *
>> + * Return: 0 - no error, -1 - unhandled cases
>> + */
>> +static int gather_folio_orders(char *vaddr_start, size_t len,
>> +			       int pagemap_fd, int kpageflags_fd,
>> +			       int orders[], int nr_orders)
>> +{
>> +	uint64_t page_flags = 0;
>> +	int cur_order = -1;
>> +	char *vaddr;
>> +
>> +	if (!pagemap_fd || !kpageflags_fd)
>> +		return -1;
>> +	if (nr_orders <= 0)
>> +		return -1;
>> +
>> +	for (vaddr = vaddr_start; vaddr < vaddr_start + len;) {
>> +		char *next_folio_vaddr;
>> +		int status;
>> +
>> +		status = get_page_flags(vaddr, pagemap_fd, kpageflags_fd,
>> +					&page_flags);
>> +		if (status < 0)
>> +			return -1;
>> +
>> +		/* skip non present vaddr */
>> +		if (status == 1) {
>> +			vaddr += psize();
>> +			continue;
>> +		}
>> +
>> +		/* all order-0 pages with possible false postive (non folio) */
>> +		if (!(page_flags & (KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))) {
>> +			orders[0]++;
>> +			vaddr += psize();
>> +			continue;
>> +		}
>> +
>> +		/* skip non thp compound pages */
>> +		if (!(page_flags & KPF_THP)) {
>> +			vaddr += psize();
>> +			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;
>> +
>> +			vaddr += psize();
>> +			continue;
>> +		}
>> +
>> +		next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
>> +
>> +		if (next_folio_vaddr >= vaddr_start + len)
>> +			break;
>> +
>> +		while ((status = get_page_flags(next_folio_vaddr, pagemap_fd,
>> +						 kpageflags_fd,
>> +						 &page_flags)) >= 0) {
>> +			/*
>> +			 * non present vaddr, next compound head page, or
>> +			 * order-0 page
>> +			 */
>> +			if (status == 1 ||
>> +			    (page_flags & KPF_COMPOUND_HEAD) ||
>> +			    !(page_flags & (KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))) {
>> +				if (cur_order < nr_orders) {
>> +					orders[cur_order]++;
>> +					cur_order = -1;
>> +					vaddr = next_folio_vaddr;
>> +				}
>> +				break;
>> +			}
>> +
>> +			/* not a head nor a tail in a THP? */
>> +			if (!(page_flags & KPF_COMPOUND_TAIL))
>> +				return -1;
>> +
>> +			cur_order++;
>> +			next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
>> +		}
>> +
>> +		if (status < 0)
>> +			return status;
>> +	}
>> +	if (cur_order > 0 && cur_order < nr_orders)
>> +		orders[cur_order]++;
>> +	return 0;
>> +}
>> +
>> +int check_folio_orders(char *vaddr_start, size_t len, int pagemap_fd,
>> +			int kpageflags_fd, int orders[], int nr_orders)
>> +{
>> +	int *vaddr_orders;
>> +	int status;
>> +	int i;
>> +
>> +	vaddr_orders = (int *)malloc(sizeof(int) * nr_orders);
>> +
>> +	if (!vaddr_orders)
>> +		ksft_exit_fail_msg("Cannot allocate memory for vaddr_orders");
>> +
>> +	memset(vaddr_orders, 0, sizeof(int) * nr_orders);
>> +	status = gather_folio_orders(vaddr_start, len, pagemap_fd,
>> +				     kpageflags_fd, vaddr_orders, nr_orders);
>> +	if (status)
>> +		goto out;
>> +
>> +	status = 0;
>
> Nit.
> It seems redundant.
> Would you consider removing it for a bit more conciseness?
> This doesn't block my approval, of course.
> Reviewed-by: wang lian <lianux.mm@gmail.com>

Sure. Thanks.

Best Regards,
Yan, Zi