and rename it to is_backed_by_folio().

is_backed_by_folio() checks if the given vaddr is backed a folio with
a given order. It does so by:
1. getting the pfn of the vaddr;
2. checking kpageflags of the pfn;

if order is greater than 0:
3. checking kpageflags of the head pfn;
4. checking kpageflags of all tail pfns.

pmd_order is added to split_huge_page_test.c and replaces max_order.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 .../selftests/mm/split_huge_page_test.c       | 67 +++++++++++++------
 tools/testing/selftests/mm/vm_util.c          |  2 +-
 tools/testing/selftests/mm/vm_util.h          |  1 +
 3 files changed, 48 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 63ac82f0b9e0..3aaf783f339f 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -25,6 +25,7 @@
 uint64_t pagesize;
 unsigned int pageshift;
 uint64_t pmd_pagesize;
+unsigned int pmd_order;
 
 #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
 #define SMAP_PATH "/proc/self/smaps"
@@ -36,23 +37,48 @@ uint64_t pmd_pagesize;
 
 #define GET_ORDER(nr_pages)    (31 - __builtin_clz(nr_pages))
 
-int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
+int is_backed_by_folio(char *vaddr, int order, int pagemap_fd, int kpageflags_fd)
 {
-	uint64_t paddr;
-	uint64_t page_flags;
+	unsigned long pfn_head;
+	uint64_t pfn_flags;
+	unsigned long pfn;
+	unsigned long i;
 
-	if (pagemap_file) {
-		pread(pagemap_file, &paddr, sizeof(paddr),
-			((long)vaddr >> pageshift) * sizeof(paddr));
+	if (!pagemap_fd || !kpageflags_fd)
+		return 0;
 
-		if (kpageflags_file) {
-			pread(kpageflags_file, &page_flags, sizeof(page_flags),
-				PAGEMAP_PFN(paddr) * sizeof(page_flags));
+	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
 
-			return !!(page_flags & KPF_THP);
-		}
+	if (pfn == -1UL)
+		return 0;
+
+	if (get_pfn_flags(pfn, kpageflags_fd, &pfn_flags))
+		return 0;
+
+	if (!order) {
+		if (pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))
+			return 0;
+		return 1;
 	}
-	return 0;
+
+	if (!(pfn_flags & KPF_THP))
+		return 0;
+
+	pfn_head = pfn & ~((1 << order) - 1);
+
+	if (get_pfn_flags(pfn_head, kpageflags_fd, &pfn_flags))
+		return 0;
+
+	if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD)))
+		return 0;
+
+	for (i = 1; i < (1UL << order) - 1; i++) {
+		if (get_pfn_flags(pfn_head + i, kpageflags_fd, &pfn_flags))
+			return 0;
+		if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL)))
+			return 0;
+	}
+	return 1;
 }
 
 static void write_file(const char *path, const char *buf, size_t buflen)
@@ -233,7 +259,7 @@ void split_pte_mapped_thp(void)
 	thp_size = 0;
 	for (i = 0; i < pagesize * 4; i++)
 		if (i % pagesize == 0 &&
-		    is_backed_by_thp(&pte_mapped[i], pagemap_fd, kpageflags_fd))
+		    is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd))
 			thp_size++;
 
 	if (thp_size != 4)
@@ -250,7 +276,7 @@ void split_pte_mapped_thp(void)
 			ksft_exit_fail_msg("%ld byte corrupted\n", i);
 
 		if (i % pagesize == 0 &&
-		    is_backed_by_thp(&pte_mapped[i], pagemap_fd, kpageflags_fd))
+		    !is_backed_by_folio(&pte_mapped[i], 0, pagemap_fd, kpageflags_fd))
 			thp_size++;
 	}
 
@@ -522,7 +548,6 @@ int main(int argc, char **argv)
 	const char *fs_loc;
 	bool created_tmp;
 	int offset;
-	unsigned int max_order;
 	unsigned int nr_pages;
 	unsigned int tests;
 
@@ -543,28 +568,28 @@ int main(int argc, char **argv)
 		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
 
 	nr_pages = pmd_pagesize / pagesize;
-	max_order = GET_ORDER(nr_pages);
-	tests = 2 + (max_order - 1) + (2 * max_order) + (max_order - 1) * 4 + 2;
+	pmd_order = GET_ORDER(nr_pages);
+	tests = 2 + (pmd_order - 1) + (2 * pmd_order) + (pmd_order - 1) * 4 + 2;
 	ksft_set_plan(tests);
 
 	fd_size = 2 * pmd_pagesize;
 
 	split_pmd_zero_pages();
 
-	for (i = 0; i < max_order; i++)
+	for (i = 0; i < pmd_order; i++)
 		if (i != 1)
 			split_pmd_thp_to_order(i);
 
 	split_pte_mapped_thp();
-	for (i = 0; i < max_order; i++)
+	for (i = 0; i < pmd_order; i++)
 		split_file_backed_thp(i);
 
 	created_tmp = prepare_thp_fs(optional_xfs_path, fs_loc_template,
 			&fs_loc);
-	for (i = max_order - 1; i >= 0; i--)
+	for (i = pmd_order - 1; i >= 0; i--)
 		split_thp_in_pagecache_to_order_at(fd_size, fs_loc, i, -1);
 
-	for (i = 0; i < max_order; i++)
+	for (i = 0; i < pmd_order; i++)
 		for (offset = 0;
 		     offset < nr_pages;
 		     offset += MAX(nr_pages / 4, 1 << i))
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 4d952d1bc96d..193ba1a1a3cc 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -338,7 +338,7 @@ 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)
+int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
 {
 	size_t count;
 
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 02e3f1e7065b..148b792cff0f 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -92,6 +92,7 @@ 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 get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);
-- 
2.47.2

On Tue, Aug 12, 2025 at 11:55:11AM -0400, Zi Yan wrote:
>and rename it to is_backed_by_folio().
>
>is_backed_by_folio() checks if the given vaddr is backed a folio with
>a given order. It does so by:
>1. getting the pfn of the vaddr;
>2. checking kpageflags of the pfn;
>
>if order is greater than 0:
>3. checking kpageflags of the head pfn;
>4. checking kpageflags of all tail pfns.
>
>pmd_order is added to split_huge_page_test.c and replaces max_order.
>
>Signed-off-by: Zi Yan <ziy@nvidia.com>
>---
> .../selftests/mm/split_huge_page_test.c       | 67 +++++++++++++------
> tools/testing/selftests/mm/vm_util.c          |  2 +-
> tools/testing/selftests/mm/vm_util.h          |  1 +
> 3 files changed, 48 insertions(+), 22 deletions(-)
>
>diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>index 63ac82f0b9e0..3aaf783f339f 100644
>--- a/tools/testing/selftests/mm/split_huge_page_test.c
>+++ b/tools/testing/selftests/mm/split_huge_page_test.c
>@@ -25,6 +25,7 @@
> uint64_t pagesize;
> unsigned int pageshift;
> uint64_t pmd_pagesize;
>+unsigned int pmd_order;
> 
> #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
> #define SMAP_PATH "/proc/self/smaps"
>@@ -36,23 +37,48 @@ uint64_t pmd_pagesize;
> 
> #define GET_ORDER(nr_pages)    (31 - __builtin_clz(nr_pages))
> 
>-int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>+int is_backed_by_folio(char *vaddr, int order, int pagemap_fd, int kpageflags_fd)
> {
>-	uint64_t paddr;
>-	uint64_t page_flags;
>+	unsigned long pfn_head;
>+	uint64_t pfn_flags;
>+	unsigned long pfn;
>+	unsigned long i;
> 
>-	if (pagemap_file) {
>-		pread(pagemap_file, &paddr, sizeof(paddr),
>-			((long)vaddr >> pageshift) * sizeof(paddr));
>+	if (!pagemap_fd || !kpageflags_fd)
>+		return 0;

The same in patch 2.

> 
>-		if (kpageflags_file) {
>-			pread(kpageflags_file, &page_flags, sizeof(page_flags),
>-				PAGEMAP_PFN(paddr) * sizeof(page_flags));
>+	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
> 
>-			return !!(page_flags & KPF_THP);
>-		}
>+	if (pfn == -1UL)
>+		return 0;
>+
>+	if (get_pfn_flags(pfn, kpageflags_fd, &pfn_flags))
>+		return 0;
>+
>+	if (!order) {
>+		if (pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))
>+			return 0;
>+		return 1;
> 	}
>-	return 0;
>+
>+	if (!(pfn_flags & KPF_THP))
>+		return 0;
>+
>+	pfn_head = pfn & ~((1 << order) - 1);
>+
>+	if (get_pfn_flags(pfn_head, kpageflags_fd, &pfn_flags))
>+		return 0;
>+
>+	if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD)))
>+		return 0;
>+
>+	for (i = 1; i < (1UL << order) - 1; i++) {

Do we miss the last tail?

>+		if (get_pfn_flags(pfn_head + i, kpageflags_fd, &pfn_flags))
>+			return 0;
>+		if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL)))
>+			return 0;
>+	}

If this folio is larger than order, would it still return 1?

>+	return 1;
> }
> 
> static void write_file(const char *path, const char *buf, size_t buflen)
>@@ -233,7 +259,7 @@ void split_pte_mapped_thp(void)
> 	thp_size = 0;
> 	for (i = 0; i < pagesize * 4; i++)
> 		if (i % pagesize == 0 &&
>-		    is_backed_by_thp(&pte_mapped[i], pagemap_fd, kpageflags_fd))
>+		    is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd))
> 			thp_size++;
> 
> 	if (thp_size != 4)
>@@ -250,7 +276,7 @@ void split_pte_mapped_thp(void)
> 			ksft_exit_fail_msg("%ld byte corrupted\n", i);
> 
> 		if (i % pagesize == 0 &&
>-		    is_backed_by_thp(&pte_mapped[i], pagemap_fd, kpageflags_fd))
>+		    !is_backed_by_folio(&pte_mapped[i], 0, pagemap_fd, kpageflags_fd))
> 			thp_size++;
> 	}
> 
>@@ -522,7 +548,6 @@ int main(int argc, char **argv)
> 	const char *fs_loc;
> 	bool created_tmp;
> 	int offset;
>-	unsigned int max_order;
> 	unsigned int nr_pages;
> 	unsigned int tests;
> 
>@@ -543,28 +568,28 @@ int main(int argc, char **argv)
> 		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
> 
> 	nr_pages = pmd_pagesize / pagesize;
>-	max_order = GET_ORDER(nr_pages);
>-	tests = 2 + (max_order - 1) + (2 * max_order) + (max_order - 1) * 4 + 2;
>+	pmd_order = GET_ORDER(nr_pages);
>+	tests = 2 + (pmd_order - 1) + (2 * pmd_order) + (pmd_order - 1) * 4 + 2;
> 	ksft_set_plan(tests);
> 
> 	fd_size = 2 * pmd_pagesize;
> 
> 	split_pmd_zero_pages();
> 
>-	for (i = 0; i < max_order; i++)
>+	for (i = 0; i < pmd_order; i++)
> 		if (i != 1)
> 			split_pmd_thp_to_order(i);
> 
> 	split_pte_mapped_thp();
>-	for (i = 0; i < max_order; i++)
>+	for (i = 0; i < pmd_order; i++)
> 		split_file_backed_thp(i);
> 
> 	created_tmp = prepare_thp_fs(optional_xfs_path, fs_loc_template,
> 			&fs_loc);
>-	for (i = max_order - 1; i >= 0; i--)
>+	for (i = pmd_order - 1; i >= 0; i--)
> 		split_thp_in_pagecache_to_order_at(fd_size, fs_loc, i, -1);
> 
>-	for (i = 0; i < max_order; i++)
>+	for (i = 0; i < pmd_order; i++)
> 		for (offset = 0;
> 		     offset < nr_pages;
> 		     offset += MAX(nr_pages / 4, 1 << i))
>diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
>index 4d952d1bc96d..193ba1a1a3cc 100644
>--- a/tools/testing/selftests/mm/vm_util.c
>+++ b/tools/testing/selftests/mm/vm_util.c
>@@ -338,7 +338,7 @@ 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)
>+int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
> {
> 	size_t count;
> 
>diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
>index 02e3f1e7065b..148b792cff0f 100644
>--- a/tools/testing/selftests/mm/vm_util.h
>+++ b/tools/testing/selftests/mm/vm_util.h
>@@ -92,6 +92,7 @@ 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 get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags);
> 
> 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 13 Aug 2025, at 17:41, Wei Yang wrote:

> On Tue, Aug 12, 2025 at 11:55:11AM -0400, Zi Yan wrote:
>> and rename it to is_backed_by_folio().
>>
>> is_backed_by_folio() checks if the given vaddr is backed a folio with
>> a given order. It does so by:
>> 1. getting the pfn of the vaddr;
>> 2. checking kpageflags of the pfn;
>>
>> if order is greater than 0:
>> 3. checking kpageflags of the head pfn;
>> 4. checking kpageflags of all tail pfns.
>>
>> pmd_order is added to split_huge_page_test.c and replaces max_order.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>> .../selftests/mm/split_huge_page_test.c       | 67 +++++++++++++------
>> tools/testing/selftests/mm/vm_util.c          |  2 +-
>> tools/testing/selftests/mm/vm_util.h          |  1 +
>> 3 files changed, 48 insertions(+), 22 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>> index 63ac82f0b9e0..3aaf783f339f 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -25,6 +25,7 @@
>> uint64_t pagesize;
>> unsigned int pageshift;
>> uint64_t pmd_pagesize;
>> +unsigned int pmd_order;
>>
>> #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
>> #define SMAP_PATH "/proc/self/smaps"
>> @@ -36,23 +37,48 @@ uint64_t pmd_pagesize;
>>
>> #define GET_ORDER(nr_pages)    (31 - __builtin_clz(nr_pages))
>>
>> -int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>> +int is_backed_by_folio(char *vaddr, int order, int pagemap_fd, int kpageflags_fd)
>> {
>> -	uint64_t paddr;
>> -	uint64_t page_flags;
>> +	unsigned long pfn_head;
>> +	uint64_t pfn_flags;
>> +	unsigned long pfn;
>> +	unsigned long i;
>>
>> -	if (pagemap_file) {
>> -		pread(pagemap_file, &paddr, sizeof(paddr),
>> -			((long)vaddr >> pageshift) * sizeof(paddr));
>> +	if (!pagemap_fd || !kpageflags_fd)
>> +		return 0;
>
> The same in patch 2.

Will fix it.

>
>>
>> -		if (kpageflags_file) {
>> -			pread(kpageflags_file, &page_flags, sizeof(page_flags),
>> -				PAGEMAP_PFN(paddr) * sizeof(page_flags));
>> +	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
>>
>> -			return !!(page_flags & KPF_THP);
>> -		}
>> +	if (pfn == -1UL)
>> +		return 0;
>> +
>> +	if (get_pfn_flags(pfn, kpageflags_fd, &pfn_flags))
>> +		return 0;
>> +
>> +	if (!order) {
>> +		if (pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))
>> +			return 0;
>> +		return 1;
>> 	}
>> -	return 0;
>> +
>> +	if (!(pfn_flags & KPF_THP))
>> +		return 0;
>> +
>> +	pfn_head = pfn & ~((1 << order) - 1);
>> +
>> +	if (get_pfn_flags(pfn_head, kpageflags_fd, &pfn_flags))
>> +		return 0;
>> +
>> +	if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD)))
>> +		return 0;
>> +
>> +	for (i = 1; i < (1UL << order) - 1; i++) {
>
> Do we miss the last tail?

Yes, will fix it.

>
>> +		if (get_pfn_flags(pfn_head + i, kpageflags_fd, &pfn_flags))
>> +			return 0;
>> +		if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL)))
>> +			return 0;
>> +	}
>
> If this folio is larger than order, would it still return 1?

Yes, but it should be good enough for current use. Will add a comment about it.

Thanks for the review.

Best Regards,
Yan, Zi