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

[Baolin Wang <baolin.wang@linux.alibaba.com>]

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?

> +
> +	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'?

> +			       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)?

> +	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);