Re: [PATCH v2 2/3] selftests/mm: add check_folio_orders() helper.

[Donet Tom <donettom@linux.ibm.com>]

On 8/9/25 12:31 AM, 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>
> ---
>   .../selftests/mm/split_huge_page_test.c       |   4 +-
>   tools/testing/selftests/mm/vm_util.c          | 133 ++++++++++++++++++
>   tools/testing/selftests/mm/vm_util.h          |   7 +
>   3 files changed, 141 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 cb364c5670c6..5ab488fab1cd 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..41d50b74b2f6 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -338,6 +338,139 @@ int detect_hugetlb_page_sizes(size_t sizes[], int max)
>   	return count;
>   }
>   
> +static int get_page_flags(char *vaddr, int pagemap_file, int kpageflags_file,
> +			  uint64_t *flags)
> +{
> +	unsigned long pfn;
> +	size_t count;
> +
> +	pfn = pagemap_get_pfn(pagemap_file, 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 0;
> +	}
> +
> +	count = pread(kpageflags_file, flags, sizeof(*flags),
> +		      pfn * sizeof(*flags));
> +
> +	if (count != sizeof(*flags))
> +		return -1;
> +
> +	return 0;
> +}
> +
> +static int gather_folio_orders(char *vaddr_start, size_t len,
> +			       int pagemap_file, int kpageflags_file,
> +			       int orders[], int nr_orders)
> +{
> +	uint64_t page_flags = 0;
> +	int cur_order = -1;
> +	char *vaddr;
> +
> +	if (!pagemap_file || !kpageflags_file)
> +		return -1;
> +	if (nr_orders <= 0)
> +		return -1;
> +
> +	for (vaddr = vaddr_start; vaddr < vaddr_start + len; ) {
> +		char *next_folio_vaddr;
> +		int status;
> +
> +		if (get_page_flags(vaddr, 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]++;
> +			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;
> +			continue;

If KPF_COMPOUND_TAIL is set, do we use the same vaddr, or should we 
advance to the next vaddr before continuing?


> +		}
> +
> +		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_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;
> +					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)
> +			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_file,
> +			int kpageflags_file, 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_file,
> +				     kpageflags_file, vaddr_orders, nr_orders);
> +	if (status)
> +		return status;
> +
> +	status = 0;
> +	for (i = 0; i < nr_orders; i++)
> +		if (vaddr_orders[i] != orders[i]) {
> +			ksft_print_msg("order %d: expected: %d got %d\n", i,
> +				       orders[i], vaddr_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 1843ad48d32b..02e3f1e7065b 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -18,6 +18,11 @@
>   #define PM_SWAP                       BIT_ULL(62)
>   #define PM_PRESENT                    BIT_ULL(63)
>   
> +#define KPF_COMPOUND_HEAD             BIT_ULL(15)
> +#define KPF_COMPOUND_TAIL             BIT_ULL(16)
> +#define KPF_THP                       BIT_ULL(22)
> +
> +
>   /*
>    * Ignore the checkpatch warning, we must read from x but don't want to do
>    * anything with it in order to trigger a read page fault. We therefore must use
> @@ -85,6 +90,8 @@ 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(char *vaddr_start, size_t len, 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);