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;
+		}
+
+		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);
-- 
2.47.2

On 2025/8/9 03:01, 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(-)
> 

[snip]

> +
> +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)

Missed calling free(vaddr_orders) before returning.

> +		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;
> +		}
> +

Ditto.

> +	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);

On 11 Aug 2025, at 3:52, Baolin Wang wrote:

> On 2025/8/9 03:01, 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(-)
>>
>
> [snip]
>
>> +
>> +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)
>
> Missed calling free(vaddr_orders) before returning.
>
>> +		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;
>> +		}
>> +
>
> Ditto.
>
>> +	return status;
>> +}
>> +

Will add free() in the above two locations. Thank you for spotting them.

Best Regards,
Yan, Zi

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);

On 10 Aug 2025, at 12:49, Donet Tom wrote:

> 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?

Yeah, I missed a vaddr += psize() here. Thank you for pointing this out.

Best Regards,
Yan, Zi

On Fri, Aug 08, 2025 at 03:01:43PM -0400, 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));
> 

is_backed_by_thp() shares similar logic as get_page_flags(), I am thinking we can
leverage get_page_flags() here.

> 			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)
>+{

Nit.

In vm_util.c, we usually name the file descriptor as xxx_fd.

>+	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;
>+}
>+

Maybe a simple document here would be helpful.

>+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;
>+		}
>+
>+		next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
>+
>+		if (next_folio_vaddr >= vaddr_start + len)
>+			break;

Would we skip order 1 folio at the last position?

For example, vaddr_start is 0x2000, len is 0x2000 and the folio at vaddr_start
is an order 1 folio, whose size is exactly 0x2000.

Then we will get next_folio_vaddr == vaddr_start + len.

Could that happen?

>+
>+		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))) {

Maybe we can put them into one line.

>+				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()));
>+		}

The while loop share similar logic as the outer for loop. Is it possible
reduce some duplication?

>+
>+		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);
>+

I took a look into thp_setting.h, where defines an array with NR_ORDERS
element which is 20. Maybe we can leverage it here, since we don't expect the
order to be larger.

>+	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);
>-- 
>2.47.2

-- 
Wei Yang
Help you, Help me

On 9 Aug 2025, at 16:18, Wei Yang wrote:

> On Fri, Aug 08, 2025 at 03:01:43PM -0400, 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));
>>
>
> is_backed_by_thp() shares similar logic as get_page_flags(), I am thinking we can
> leverage get_page_flags() here.

I was lazy for this one. I will use check_folio_orders() in the next version.

>
>> 			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)
>> +{
>
> Nit.
>
> In vm_util.c, we usually name the file descriptor as xxx_fd.

OK. I can rename them.
>
>> +	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;
>> +}
>> +
>
> Maybe a simple document here would be helpful.

Will do.

>
>> +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;
>> +		}
>> +
>> +		next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
>> +
>> +		if (next_folio_vaddr >= vaddr_start + len)
>> +			break;
>
> Would we skip order 1 folio at the last position?
>
> For example, vaddr_start is 0x2000, len is 0x2000 and the folio at vaddr_start
> is an order 1 folio, whose size is exactly 0x2000.
>
> Then we will get next_folio_vaddr == vaddr_start + len.
>
> Could that happen?

No. After the loop, there is code checking cur_order and updating orders[].

>
>> +
>> +		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))) {
>
> Maybe we can put them into one line.

Sure.

>
>> +				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()));
>> +		}
>
> The while loop share similar logic as the outer for loop. Is it possible
> reduce some duplication?

Outer loop is to filter order-0 and non head pages and while loop is
to find current THP/mTHP orders. It would be messy to combine them.
But feel free to provide ideas if you see a way.

>
>> +
>> +		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);
>> +
>
> I took a look into thp_setting.h, where defines an array with NR_ORDERS
> element which is 20. Maybe we can leverage it here, since we don't expect the
> order to be larger.
>

20 is too large for current use. We can revisit this when the function
gets more users.

>> +	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);
>> -- 
>> 2.47.2
>
> -- 
> Wei Yang
> Help you, Help me


Best Regards,
Yan, Zi

On Mon, Aug 11, 2025 at 02:39:08PM -0400, Zi Yan wrote:
[...]
>>> +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;
>>> +		}
>>> +
>>> +		next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
>>> +
>>> +		if (next_folio_vaddr >= vaddr_start + len)
>>> +			break;
>>
>> Would we skip order 1 folio at the last position?
>>
>> For example, vaddr_start is 0x2000, len is 0x2000 and the folio at vaddr_start
>> is an order 1 folio, whose size is exactly 0x2000.
>>
>> Then we will get next_folio_vaddr == vaddr_start + len.
>>
>> Could that happen?
>
>No. After the loop, there is code checking cur_order and updating orders[].
>

Oh, I missed this.

-- 
Wei Yang
Help you, Help me