[PATCH 0/2] kselftest: mm: fix some failure of split_huge_page_test

[PATCH 0/2] kselftest: mm: fix some failure of split_huge_page_test

[Yeoreum Yun]

split_huge_page_test can fail for the following reasons:

  1. During the test, khugepaged may collapse previously split pages again,
     causing intermittent failures.

  2. Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
     glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
     made by memalign(). The underlying VMA may start at a different address
     from the aligned address returned by memalign(). Moreover, a subsequent
     madvise(MADV_HUGEPAGE) call does not split the VMA because it already
     has the same advice.

     This causes the test to fail because the check_huge_xxx() helpers
     incorrectly require the address returned by memalign() to match the
     VMA start address reported in /proc/self/smaps.

Address these issues by applying MADV_NOHUGEPAGE after faulting in the
huge page, preventing khugepaged from collapsing it again, and by replacing
the use of /proc/self/smaps in the check_huge_xxx() helpers with
/proc/self/pagemap and /proc/kpageflags.

This patch based on v7.2

---
Yeoreum Yun (2):
      kselftest: mm: prevent random failure of huge page split for khugepaged
      kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

 tools/testing/selftests/mm/khugepaged.c           |  26 ++---
 tools/testing/selftests/mm/split_huge_page_test.c |  17 ++-
 tools/testing/selftests/mm/vm_util.c              | 135 ++++++++++++++++++----
 tools/testing/selftests/mm/vm_util.h              |   1 +
 4 files changed, 142 insertions(+), 37 deletions(-)
---
base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
change-id: 20260820-fix_split-f44939ec44b8

Best regards,
-- 
Sincerely,
Yeoreum Yun

[PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged

[Yeoreum Yun]

There're some random failure for split_huge_page_test when khugepaged
collapses pages into pmd again which had split by the test.

Prevent the khugepaged's collapses for split page by setting the
mapped pmd-huge-page with MADV_NOHUGEPAGE before split.

Reported-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 tools/testing/selftests/mm/split_huge_page_test.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 32b991472f744..99b45e5518199 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -303,6 +303,9 @@ static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp
 	if (!rss_anon_before)
 		ksft_exit_fail_msg("No RssAnon is allocated before split\n");
 
+	/* Prevent khugepaged from collapsing the pages. */
+	madvise(one_page, len, MADV_NOHUGEPAGE);
+
 	/* split all THPs */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
 		      (uint64_t)one_page + len, 0);
@@ -350,6 +353,9 @@ static void split_pmd_thp_to_order(int order)
 	if (!check_huge_anon(one_page, 4, pmd_pagesize))
 		ksft_exit_fail_msg("No THP is allocated\n");
 
+	/* Prevent khugepaged from collapsing the pages. */
+	madvise(one_page, len, MADV_NOHUGEPAGE);
+
 	/* split all THPs */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
 		(uint64_t)one_page + len, order);
@@ -436,6 +442,9 @@ static void split_pte_mapped_thp(void)
 		goto out;
 	}
 
+	/* Prevent khugepaged from collapsing the pages. */
+	madvise(thp_area, thp_area_size, MADV_NOHUGEPAGE);
+
 	/* Split all THPs through the remapped pages. */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)page_area,
 		      (uint64_t)page_area + page_area_size, 0);
@@ -665,6 +674,8 @@ static int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size,
 		ksft_test_result_skip("Pagecache folio split skipped\n");
 		return -2;
 	}
+	/* Prevent khugepaged from collapsing the pages. */
+	madvise(*addr, fd_size, MADV_NOHUGEPAGE);
 	return 0;
 err_out_close:
 	close(*fd);

-- 
2.43.0

[PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Yeoreum Yun]

Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
made by memalign().

The underlying VMA may start at a different address from the aligned
address returned by memalign(). Furthermore, a subsequent
madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
already set.

This causes split_huge_page_test to fail because the check_huge_xxx()
helpers incorrectly require the address returned by memalign() to
match the VMA start address reported in /proc/self/smaps.

Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
/proc/self/smaps to detect huge pages and change the meaning of
check_huge_xxx()'s nr_hpages argument:

  - nr_hpages > 0: check all of pages in the range are huge page.
  - nr_hpages < 0: check all of pages in the range are not huge page.
  - nr_hpages == 0: invalid.

Reported-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 tools/testing/selftests/mm/khugepaged.c           |  26 ++---
 tools/testing/selftests/mm/split_huge_page_test.c |   6 +-
 tools/testing/selftests/mm/vm_util.c              | 135 ++++++++++++++++++----
 tools/testing/selftests/mm/vm_util.h              |   1 +
 4 files changed, 131 insertions(+), 37 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 10e8dedcb087d..2e4665e6d5852 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -533,7 +533,7 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
 	ret = madvise_collapse_retry(p, nr_hpages * hpage_pmd_size);
 	if (((bool)ret) == expect)
 		fail("Fail: Bad return value");
-	else if (!ops->check_huge(p, expect ? nr_hpages : 0))
+	else if (!ops->check_huge(p, expect ? nr_hpages : -nr_hpages))
 		fail("Fail: check_huge()");
 	else
 		success("OK");
@@ -545,7 +545,7 @@ static void madvise_collapse(const char *msg, char *p, int nr_hpages,
 			     struct mem_ops *ops, bool expect)
 {
 	/* Sanity check */
-	if (!ops->check_huge(p, 0))
+	if (!ops->check_huge(p, -nr_hpages))
 		ksft_exit_fail_msg("Unexpected huge page\n");
 	__madvise_collapse(msg, p, nr_hpages, ops, expect);
 }
@@ -558,7 +558,7 @@ static bool wait_for_scan(const char *msg, char *p, int nr_hpages,
 	int timeout = 6; /* 3 seconds */
 
 	/* Sanity check */
-	if (!ops->check_huge(p, 0))
+	if (!ops->check_huge(p, -nr_hpages))
 		ksft_exit_fail_msg("Unexpected huge page\n");
 
 	madvise(p, nr_hpages * hpage_pmd_size, MADV_HUGEPAGE);
@@ -605,7 +605,7 @@ static void khugepaged_collapse(const char *msg, char *p, int nr_hpages,
 	if (ops != &__anon_ops)
 		ops->fault(p, 0, nr_hpages * hpage_pmd_size);
 
-	if (ops->check_huge(p, expect ? nr_hpages : 0))
+	if (ops->check_huge(p, expect ? nr_hpages : -nr_hpages))
 		success("OK");
 	else
 		fail("Fail");
@@ -643,7 +643,7 @@ static void alloc_at_fault(void)
 
 	madvise(p, page_size, MADV_DONTNEED);
 	ksft_print_msg("Split huge PMD on MADV_DONTNEED...");
-	if (check_huge_anon(p, 0, hpage_pmd_size))
+	if (check_huge_anon(p, -1, hpage_pmd_size))
 		success("OK");
 	else
 		fail("Fail");
@@ -815,7 +815,7 @@ static void collapse_single_pte_entry_compound(struct collapse_context *c, struc
 	madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
 	ksft_print_msg("Split huge page leaving single PTE mapping compound page...");
 	madvise(p + page_size, hpage_pmd_size - page_size, MADV_DONTNEED);
-	if (ops->check_huge(p, 0))
+	if (ops->check_huge(p, -1))
 		success("OK");
 	else
 		fail("Fail");
@@ -836,7 +836,7 @@ static void collapse_full_of_compound(struct collapse_context *c, struct mem_ops
 	ksft_print_msg("Split huge page leaving single PTE page table full of compound pages...");
 	madvise(p, page_size, MADV_NOHUGEPAGE);
 	madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
-	if (ops->check_huge(p, 0))
+	if (ops->check_huge(p, -1))
 		success("OK");
 	else
 		fail("Fail");
@@ -903,7 +903,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
 
 	ksft_print_msg("Allocate small page...");
 	ops->fault(p, 0, page_size);
-	if (ops->check_huge(p, 0))
+	if (ops->check_huge(p, -1))
 		success("OK");
 	else
 		fail("Fail");
@@ -911,7 +911,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
 	ksft_print_msg("Share small page over fork()...");
 	if (!fork()) {
 		/* Do not touch settings on child exit */
-		if (ops->check_huge(p, 0))
+		if (ops->check_huge(p, -1))
 			success("OK");
 		else
 			fail("Fail");
@@ -929,7 +929,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
 	exit_status = WEXITSTATUS(wstatus);
 
 	ksft_print_msg("Check if parent still has small page...");
-	if (ops->check_huge(p, 0))
+	if (ops->check_huge(p, -1))
 		success("OK");
 	else
 		fail("Fail");
@@ -955,7 +955,7 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
 		ksft_print_msg("Split huge page PMD in child process...");
 		madvise(p, page_size, MADV_NOHUGEPAGE);
 		madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
-		if (ops->check_huge(p, 0))
+		if (ops->check_huge(p, -1))
 			success("OK");
 		else
 			fail("Fail");
@@ -1003,7 +1003,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
 		ksft_print_msg("Trigger CoW on page %d of %d...",
 				hpage_pmd_nr - max_ptes_shared - 1, hpage_pmd_nr);
 		ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared - 1) * page_size);
-		if (ops->check_huge(p, 0))
+		if (ops->check_huge(p, -1))
 			success("OK");
 		else
 			fail("Fail");
@@ -1016,7 +1016,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
 			       hpage_pmd_nr - max_ptes_shared, hpage_pmd_nr);
 			ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared) *
 				    page_size);
-			if (ops->check_huge(p, 0))
+			if (ops->check_huge(p, -1))
 				success("OK");
 			else
 				fail("Fail");
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 99b45e5518199..4fcd330cf0726 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -314,7 +314,7 @@ static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp
 		if (one_page[i] != (char)0)
 			ksft_exit_fail_msg("%ld byte corrupted\n", i);
 
-	if (!check_huge_anon(one_page, 0, pmd_pagesize))
+	if (!check_huge_anon(one_page, -nr_hpages, pmd_pagesize))
 		ksft_exit_fail_msg("Still AnonHugePages not split\n");
 
 	rss_anon_after = rss_anon();
@@ -372,7 +372,7 @@ static void split_pmd_thp_to_order(int order)
 					   (pmd_order + 1)))
 		ksft_exit_fail_msg("Unexpected THP split\n");
 
-	if (!check_huge_anon(one_page, 0, pmd_pagesize))
+	if (!check_huge_anon(one_page, -4, pmd_pagesize))
 		ksft_exit_fail_msg("Still AnonHugePages not split\n");
 
 	ksft_test_result_pass("Split huge pages to order %d successful\n", order);
@@ -746,7 +746,7 @@ static void split_thp_in_pagecache_to_order_at(size_t fd_size,
 		goto out;
 	}
 
-	if (!check_huge_file(addr, 0, pmd_pagesize)) {
+	if (!check_huge_file(addr, -(fd_size / pmd_pagesize), pmd_pagesize)) {
 		ksft_print_msg("Still FilePmdMapped not split\n");
 		err = EXIT_FAILURE;
 		goto out;
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 311fc5b4513eb..166d5d79289f3 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -14,6 +14,8 @@
 #define PMD_SIZE_FILE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
 #define SMAP_FILE_PATH "/proc/self/smaps"
 #define STATUS_FILE_PATH "/proc/self/status"
+#define PAGEMAP_FILE_PATH "/proc/self/pagemap"
+#define KPAGEFLAGS_FILE_PATH "/proc/kpageflags"
 #define MAX_LINE_LENGTH 500
 
 unsigned int __page_size;
@@ -229,37 +231,128 @@ char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
 	return entry;
 }
 
-bool __check_huge(void *addr, char *pattern, int nr_hpages,
-		  uint64_t hpage_size)
-{
-	char buffer[MAX_LINE_LENGTH];
-	uint64_t thp = -1;
-	char *entry;
-
-	entry = __get_smap_entry(addr, pattern, buffer, sizeof(buffer));
-	if (!entry)
-		goto err_out;
-
-	if (sscanf(entry, "%9" SCNu64 " kB", &thp) != 1)
-		ksft_exit_fail_msg("Reading smap error\n");
-
-err_out:
-	return thp == (nr_hpages * (hpage_size >> 10));
-}
-
 bool check_huge_anon(void *addr, int nr_hpages, uint64_t hpage_size)
 {
-	return __check_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
+	int i, pagemap_fd, nr = 0;
+	uint64_t categories;
+	bool expect_huge;
+
+	if (nr_hpages == 0 || hpage_size == 0)
+		return false;
+
+	if (nr_hpages < 0) {
+		nr_hpages = -nr_hpages;
+		expect_huge = false;
+	} else
+		expect_huge = true;
+
+	pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
+
+	for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
+		categories = pagemap_scan_get_categories(pagemap_fd, addr);
+		if (!(categories & PAGE_IS_HUGE))
+			continue;
+		if (categories & PAGE_IS_FILE)
+			continue;
+		nr++;
+	}
+
+	close(pagemap_fd);
+	return expect_huge ? nr == nr_hpages : nr == 0;
 }
 
 bool check_huge_file(void *addr, int nr_hpages, uint64_t hpage_size)
 {
-	return __check_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size);
+	int i, pagemap_fd, kpf_fd, nr = 0;
+	unsigned long pfn;
+	uint64_t categories, kpf;
+	bool expect_huge;
+
+	if (nr_hpages == 0 || hpage_size == 0)
+		return false;
+
+	if (nr_hpages < 0) {
+		nr_hpages = -nr_hpages;
+		expect_huge = false;
+	} else
+		expect_huge = true;
+
+	pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
+
+	kpf_fd = open(KPAGEFLAGS_FILE_PATH, O_RDONLY);
+	if (kpf_fd < 0)
+		ksft_exit_fail_msg("open kpageflags: %s\n", strerror(errno));
+
+	for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
+		categories = pagemap_scan_get_categories(pagemap_fd, addr);
+		pfn = pagemap_get_pfn(pagemap_fd, addr);
+		if (pfn == -1UL)
+			continue;
+		if (pageflags_get(pfn, kpf_fd, &kpf))
+			ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
+		if (!(categories & PAGE_IS_HUGE))
+			continue;
+		if (!(categories & PAGE_IS_FILE))
+			continue;
+		if (kpf & KPF_SWAPBACKED)
+			continue;
+		nr++;
+	}
+
+	close(pagemap_fd);
+	close(kpf_fd);
+
+	return expect_huge ? nr == nr_hpages : nr == 0;
 }
 
 bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size)
 {
-	return __check_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
+	int i, pagemap_fd, kpf_fd, nr = 0;
+	unsigned long pfn;
+	uint64_t categories, kpf;
+	bool expect_huge;
+
+	if (nr_hpages == 0 || hpage_size == 0)
+		return false;
+
+	if (nr_hpages < 0) {
+		nr_hpages = -nr_hpages;
+		expect_huge = true;
+	} else
+		expect_huge = false;
+
+	pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
+
+	kpf_fd = open(KPAGEFLAGS_FILE_PATH, O_RDONLY);
+	if (kpf_fd < 0)
+		ksft_exit_fail_msg("open kpageflags: %s\n", strerror(errno));
+
+	for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
+		categories = pagemap_scan_get_categories(pagemap_fd, addr);
+		pfn = pagemap_get_pfn(pagemap_fd, addr);
+		if (pfn == -1UL)
+			continue;
+		if (pageflags_get(pfn, kpf_fd, &kpf))
+			ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
+		if (!(categories & PAGE_IS_HUGE))
+			continue;
+		if (!(categories & PAGE_IS_FILE))
+			continue;
+		if (!(kpf & KPF_SWAPBACKED))
+			continue;
+		nr++;
+	}
+
+	close(pagemap_fd);
+	close(kpf_fd);
+
+	return expect_huge ? nr == nr_hpages : nr == 0;
 }
 
 int64_t allocate_transhuge(void *ptr, int pagemap_fd)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index ea8fc8fdf0eb0..0a1627f36efc3 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -18,6 +18,7 @@
 #define PM_SWAP                       BIT_ULL(62)
 #define PM_PRESENT                    BIT_ULL(63)
 
+#define KPF_SWAPBACKED                BIT_ULL(14)
 #define KPF_COMPOUND_HEAD             BIT_ULL(15)
 #define KPF_COMPOUND_TAIL             BIT_ULL(16)
 #define KPF_HWPOISON                  BIT_ULL(19)

-- 
2.43.0

Re: [PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged

[Zi Yan]

On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
> There're some random failure for split_huge_page_test when khugepaged
> collapses pages into pmd again which had split by the test.
>
> Prevent the khugepaged's collapses for split page by setting the
> mapped pmd-huge-page with MADV_NOHUGEPAGE before split.

Why not disable khugepaged using APIs from hugepage_setting.h?
>
> Reported-by: Kevin Brodsky <kevin.brodsky@arm.com>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>  tools/testing/selftests/mm/split_huge_page_test.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>



-- 
Best Regards,
Yan, Zi

Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Zi Yan]

On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
> Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
> glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
> made by memalign().
>
> The underlying VMA may start at a different address from the aligned
> address returned by memalign(). Furthermore, a subsequent
> madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
> already set.
>
> This causes split_huge_page_test to fail because the check_huge_xxx()
> helpers incorrectly require the address returned by memalign() to
> match the VMA start address reported in /proc/self/smaps.
>
> Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
> /proc/self/smaps to detect huge pages and change the meaning of
> check_huge_xxx()'s nr_hpages argument:

Have you checked Baolin's patches[1] in mm-new? They resue
gather_after_split_folio_orders() to reimplement check_huge_xxx(), also
based on pagemap and kpageflags. Does it fix the issue?

[1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com/

>
>   - nr_hpages > 0: check all of pages in the range are huge page.
>   - nr_hpages < 0: check all of pages in the range are not huge page.
>   - nr_hpages == 0: invalid.
>
> Reported-by: David Hildenbrand (Arm) <david@kernel.org>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>  tools/testing/selftests/mm/khugepaged.c           |  26 ++---
>  tools/testing/selftests/mm/split_huge_page_test.c |   6 +-
>  tools/testing/selftests/mm/vm_util.c              | 135 ++++++++++++++++++----
>  tools/testing/selftests/mm/vm_util.h              |   1 +
>  4 files changed, 131 insertions(+), 37 deletions(-)
>


-- 
Best Regards,
Yan, Zi

Re: [PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged

[Yeoreum Yun]

On Thu, Aug 20, 2026 at 03:51:34PM -0400, Zi Yan wrote:
> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
> > There're some random failure for split_huge_page_test when khugepaged
> > collapses pages into pmd again which had split by the test.
> >
> > Prevent the khugepaged's collapses for split page by setting the
> > mapped pmd-huge-page with MADV_NOHUGEPAGE before split.
> 
> Why not disable khugepaged using APIs from hugepage_setting.h?

Well, this also works with hugepage_save_settings() and write the
khugepaged/scan_sleep_millisecs with the maximum integer.

I don't have a strong opinion but since it seems more hackish way to
change scan_sllep_millisecs, I use madvise() with MADV_NOHUGEPATE.

Would it be better to change using APIs in hugepage_setting,h?

-- 
Sincerely,
Yeoreum Yun

Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Yeoreum Yun]

> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
> > Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
> > glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
> > made by memalign().
> >
> > The underlying VMA may start at a different address from the aligned
> > address returned by memalign(). Furthermore, a subsequent
> > madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
> > already set.
> >
> > This causes split_huge_page_test to fail because the check_huge_xxx()
> > helpers incorrectly require the address returned by memalign() to
> > match the VMA start address reported in /proc/self/smaps.
> >
> > Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
> > /proc/self/smaps to detect huge pages and change the meaning of
> > check_huge_xxx()'s nr_hpages argument:
> 
> Have you checked Baolin's patches[1] in mm-new? They resue
> gather_after_split_folio_orders() to reimplement check_huge_xxx(), also
> based on pagemap and kpageflags. Does it fix the issue?
> 
> [1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com/
>

Unfortunately, No. since __check_pmd_huge() in check_huge_xxx() still use
/proc/self/smaps [1] for pmd THP, it still has problem though ths patch
series applied.

[1] https://lore.kernel.org/all/56b16691f605426b33b5cf47319233de6127a6b3.1785985999.git.baolin.wang@linux.alibaba.com/


> >
> >   - nr_hpages > 0: check all of pages in the range are huge page.
> >   - nr_hpages < 0: check all of pages in the range are not huge page.
> >   - nr_hpages == 0: invalid.
> >
> > Reported-by: David Hildenbrand (Arm) <david@kernel.org>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> >  tools/testing/selftests/mm/khugepaged.c           |  26 ++---
> >  tools/testing/selftests/mm/split_huge_page_test.c |   6 +-
> >  tools/testing/selftests/mm/vm_util.c              | 135 ++++++++++++++++++----
> >  tools/testing/selftests/mm/vm_util.h              |   1 +
> >  4 files changed, 131 insertions(+), 37 deletions(-)
> >
> 
> 
> -- 
> Best Regards,
> Yan, Zi
> 

-- 
Sincerely,
Yeoreum Yun

Re: [PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged

[Zi Yan]

On Thu Aug 20, 2026 at 5:23 PM EDT, Yeoreum Yun wrote:
> On Thu, Aug 20, 2026 at 03:51:34PM -0400, Zi Yan wrote:
>> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
>> > There're some random failure for split_huge_page_test when khugepaged
>> > collapses pages into pmd again which had split by the test.
>> >
>> > Prevent the khugepaged's collapses for split page by setting the
>> > mapped pmd-huge-page with MADV_NOHUGEPAGE before split.
>> 
>> Why not disable khugepaged using APIs from hugepage_setting.h?
>
> Well, this also works with hugepage_save_settings() and write the
> khugepaged/scan_sleep_millisecs with the maximum integer.
>
> I don't have a strong opinion but since it seems more hackish way to
> change scan_sllep_millisecs, I use madvise() with MADV_NOHUGEPATE.
>
> Would it be better to change using APIs in hugepage_setting,h?

No. I did not realize there is no way of stopping khugepaged completely.

BTW, I am curious about your khugepaged config causing this issue.
IIRC, khugepaged scan interval is about minutes and
the time between madvise(MADV_HUGEPAGE) and the second
is_backed_by_folio() should not be that long.

For your patch, maybe you want to check the return value of madvise() to
make sure it succeeds.

Otherwise,

feel free to add

Reviewed-by: Zi Yan <ziy@nvidia.com>

Thanks.


-- 
Best Regards,
Yan, Zi

Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Yeoreum Yun]

On Thu, Aug 20, 2026 at 08:40:16PM +0100, Yeoreum Yun wrote:
> Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
> glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
> made by memalign().
> 
> The underlying VMA may start at a different address from the aligned
> address returned by memalign(). Furthermore, a subsequent
> madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
> already set.
> 
> This causes split_huge_page_test to fail because the check_huge_xxx()
> helpers incorrectly require the address returned by memalign() to
> match the VMA start address reported in /proc/self/smaps.
> 
> Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
> /proc/self/smaps to detect huge pages and change the meaning of
> check_huge_xxx()'s nr_hpages argument:
> 
>   - nr_hpages > 0: check all of pages in the range are huge page.
>   - nr_hpages < 0: check all of pages in the range are not huge page.
>   - nr_hpages == 0: invalid.
> 
> Reported-by: David Hildenbrand (Arm) <david@kernel.org>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>  tools/testing/selftests/mm/khugepaged.c           |  26 ++---
>  tools/testing/selftests/mm/split_huge_page_test.c |   6 +-
>  tools/testing/selftests/mm/vm_util.c              | 135 ++++++++++++++++++----
>  tools/testing/selftests/mm/vm_util.h              |   1 +
>  4 files changed, 131 insertions(+), 37 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> index 10e8dedcb087d..2e4665e6d5852 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -533,7 +533,7 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
>  	ret = madvise_collapse_retry(p, nr_hpages * hpage_pmd_size);
>  	if (((bool)ret) == expect)
>  		fail("Fail: Bad return value");
> -	else if (!ops->check_huge(p, expect ? nr_hpages : 0))
> +	else if (!ops->check_huge(p, expect ? nr_hpages : -nr_hpages))
>  		fail("Fail: check_huge()");
>  	else
>  		success("OK");
> @@ -545,7 +545,7 @@ static void madvise_collapse(const char *msg, char *p, int nr_hpages,
>  			     struct mem_ops *ops, bool expect)
>  {
>  	/* Sanity check */
> -	if (!ops->check_huge(p, 0))
> +	if (!ops->check_huge(p, -nr_hpages))
>  		ksft_exit_fail_msg("Unexpected huge page\n");
>  	__madvise_collapse(msg, p, nr_hpages, ops, expect);
>  }
> @@ -558,7 +558,7 @@ static bool wait_for_scan(const char *msg, char *p, int nr_hpages,
>  	int timeout = 6; /* 3 seconds */
>  
>  	/* Sanity check */
> -	if (!ops->check_huge(p, 0))
> +	if (!ops->check_huge(p, -nr_hpages))
>  		ksft_exit_fail_msg("Unexpected huge page\n");
>  
>  	madvise(p, nr_hpages * hpage_pmd_size, MADV_HUGEPAGE);
> @@ -605,7 +605,7 @@ static void khugepaged_collapse(const char *msg, char *p, int nr_hpages,
>  	if (ops != &__anon_ops)
>  		ops->fault(p, 0, nr_hpages * hpage_pmd_size);
>  
> -	if (ops->check_huge(p, expect ? nr_hpages : 0))
> +	if (ops->check_huge(p, expect ? nr_hpages : -nr_hpages))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -643,7 +643,7 @@ static void alloc_at_fault(void)
>  
>  	madvise(p, page_size, MADV_DONTNEED);
>  	ksft_print_msg("Split huge PMD on MADV_DONTNEED...");
> -	if (check_huge_anon(p, 0, hpage_pmd_size))
> +	if (check_huge_anon(p, -1, hpage_pmd_size))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -815,7 +815,7 @@ static void collapse_single_pte_entry_compound(struct collapse_context *c, struc
>  	madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
>  	ksft_print_msg("Split huge page leaving single PTE mapping compound page...");
>  	madvise(p + page_size, hpage_pmd_size - page_size, MADV_DONTNEED);
> -	if (ops->check_huge(p, 0))
> +	if (ops->check_huge(p, -1))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -836,7 +836,7 @@ static void collapse_full_of_compound(struct collapse_context *c, struct mem_ops
>  	ksft_print_msg("Split huge page leaving single PTE page table full of compound pages...");
>  	madvise(p, page_size, MADV_NOHUGEPAGE);
>  	madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
> -	if (ops->check_huge(p, 0))
> +	if (ops->check_huge(p, -1))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -903,7 +903,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
>  
>  	ksft_print_msg("Allocate small page...");
>  	ops->fault(p, 0, page_size);
> -	if (ops->check_huge(p, 0))
> +	if (ops->check_huge(p, -1))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -911,7 +911,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
>  	ksft_print_msg("Share small page over fork()...");
>  	if (!fork()) {
>  		/* Do not touch settings on child exit */
> -		if (ops->check_huge(p, 0))
> +		if (ops->check_huge(p, -1))
>  			success("OK");
>  		else
>  			fail("Fail");
> @@ -929,7 +929,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
>  	exit_status = WEXITSTATUS(wstatus);
>  
>  	ksft_print_msg("Check if parent still has small page...");
> -	if (ops->check_huge(p, 0))
> +	if (ops->check_huge(p, -1))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -955,7 +955,7 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
>  		ksft_print_msg("Split huge page PMD in child process...");
>  		madvise(p, page_size, MADV_NOHUGEPAGE);
>  		madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
> -		if (ops->check_huge(p, 0))
> +		if (ops->check_huge(p, -1))
>  			success("OK");
>  		else
>  			fail("Fail");
> @@ -1003,7 +1003,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
>  		ksft_print_msg("Trigger CoW on page %d of %d...",
>  				hpage_pmd_nr - max_ptes_shared - 1, hpage_pmd_nr);
>  		ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared - 1) * page_size);
> -		if (ops->check_huge(p, 0))
> +		if (ops->check_huge(p, -1))
>  			success("OK");
>  		else
>  			fail("Fail");
> @@ -1016,7 +1016,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
>  			       hpage_pmd_nr - max_ptes_shared, hpage_pmd_nr);
>  			ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared) *
>  				    page_size);
> -			if (ops->check_huge(p, 0))
> +			if (ops->check_huge(p, -1))
>  				success("OK");
>  			else
>  				fail("Fail");
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index 99b45e5518199..4fcd330cf0726 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -314,7 +314,7 @@ static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp
>  		if (one_page[i] != (char)0)
>  			ksft_exit_fail_msg("%ld byte corrupted\n", i);
>  
> -	if (!check_huge_anon(one_page, 0, pmd_pagesize))
> +	if (!check_huge_anon(one_page, -nr_hpages, pmd_pagesize))
>  		ksft_exit_fail_msg("Still AnonHugePages not split\n");
>  
>  	rss_anon_after = rss_anon();
> @@ -372,7 +372,7 @@ static void split_pmd_thp_to_order(int order)
>  					   (pmd_order + 1)))
>  		ksft_exit_fail_msg("Unexpected THP split\n");
>  
> -	if (!check_huge_anon(one_page, 0, pmd_pagesize))
> +	if (!check_huge_anon(one_page, -4, pmd_pagesize))
>  		ksft_exit_fail_msg("Still AnonHugePages not split\n");
>  
>  	ksft_test_result_pass("Split huge pages to order %d successful\n", order);
> @@ -746,7 +746,7 @@ static void split_thp_in_pagecache_to_order_at(size_t fd_size,
>  		goto out;
>  	}
>  
> -	if (!check_huge_file(addr, 0, pmd_pagesize)) {
> +	if (!check_huge_file(addr, -(fd_size / pmd_pagesize), pmd_pagesize)) {
>  		ksft_print_msg("Still FilePmdMapped not split\n");
>  		err = EXIT_FAILURE;
>  		goto out;
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 311fc5b4513eb..166d5d79289f3 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -14,6 +14,8 @@
>  #define PMD_SIZE_FILE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
>  #define SMAP_FILE_PATH "/proc/self/smaps"
>  #define STATUS_FILE_PATH "/proc/self/status"
> +#define PAGEMAP_FILE_PATH "/proc/self/pagemap"
> +#define KPAGEFLAGS_FILE_PATH "/proc/kpageflags"
>  #define MAX_LINE_LENGTH 500
>  
>  unsigned int __page_size;
> @@ -229,37 +231,128 @@ char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
>  	return entry;
>  }
>  
> -bool __check_huge(void *addr, char *pattern, int nr_hpages,
> -		  uint64_t hpage_size)
> -{
> -	char buffer[MAX_LINE_LENGTH];
> -	uint64_t thp = -1;
> -	char *entry;
> -
> -	entry = __get_smap_entry(addr, pattern, buffer, sizeof(buffer));
> -	if (!entry)
> -		goto err_out;
> -
> -	if (sscanf(entry, "%9" SCNu64 " kB", &thp) != 1)
> -		ksft_exit_fail_msg("Reading smap error\n");
> -
> -err_out:
> -	return thp == (nr_hpages * (hpage_size >> 10));
> -}
> -
>  bool check_huge_anon(void *addr, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
> +	int i, pagemap_fd, nr = 0;
> +	uint64_t categories;
> +	bool expect_huge;
> +
> +	if (nr_hpages == 0 || hpage_size == 0)
> +		return false;
> +
> +	if (nr_hpages < 0) {
> +		nr_hpages = -nr_hpages;
> +		expect_huge = false;
> +	} else
> +		expect_huge = true;
> +
> +	pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
> +	if (pagemap_fd < 0)
> +		ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
> +
> +	for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
> +		categories = pagemap_scan_get_categories(pagemap_fd, addr);
> +		if (!(categories & PAGE_IS_HUGE))
> +			continue;
> +		if (categories & PAGE_IS_FILE)
> +			continue;
> +		nr++;
> +	}
> +
> +	close(pagemap_fd);
> +	return expect_huge ? nr == nr_hpages : nr == 0;
>  }
>  
>  bool check_huge_file(void *addr, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size);
> +	int i, pagemap_fd, kpf_fd, nr = 0;
> +	unsigned long pfn;
> +	uint64_t categories, kpf;
> +	bool expect_huge;
> +
> +	if (nr_hpages == 0 || hpage_size == 0)
> +		return false;
> +
> +	if (nr_hpages < 0) {
> +		nr_hpages = -nr_hpages;
> +		expect_huge = false;
> +	} else
> +		expect_huge = true;
> +
> +	pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
> +	if (pagemap_fd < 0)
> +		ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
> +
> +	kpf_fd = open(KPAGEFLAGS_FILE_PATH, O_RDONLY);
> +	if (kpf_fd < 0)
> +		ksft_exit_fail_msg("open kpageflags: %s\n", strerror(errno));
> +
> +	for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
> +		categories = pagemap_scan_get_categories(pagemap_fd, addr);
> +		pfn = pagemap_get_pfn(pagemap_fd, addr);
> +		if (pfn == -1UL)
> +			continue;
> +		if (pageflags_get(pfn, kpf_fd, &kpf))
> +			ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
> +		if (!(categories & PAGE_IS_HUGE))
> +			continue;
> +		if (!(categories & PAGE_IS_FILE))
> +			continue;
> +		if (kpf & KPF_SWAPBACKED)
> +			continue;
> +		nr++;
> +	}
> +
> +	close(pagemap_fd);
> +	close(kpf_fd);
> +
> +	return expect_huge ? nr == nr_hpages : nr == 0;
>  }
>  
>  bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
> +	int i, pagemap_fd, kpf_fd, nr = 0;
> +	unsigned long pfn;
> +	uint64_t categories, kpf;
> +	bool expect_huge;
> +
> +	if (nr_hpages == 0 || hpage_size == 0)
> +		return false;
> +
> +	if (nr_hpages < 0) {
> +		nr_hpages = -nr_hpages;
> +		expect_huge = true;
> +	} else
> +		expect_huge = false;
> +

Oops... this part has mistaked compared with other function...
I'll fix later...

-- 
Sincerely,
Yeoreum Yun

Re: [PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged

[Yeoreum Yun]

On Thu, Aug 20, 2026 at 07:37:29PM -0400, Zi Yan wrote:
> On Thu Aug 20, 2026 at 5:23 PM EDT, Yeoreum Yun wrote:
> > On Thu, Aug 20, 2026 at 03:51:34PM -0400, Zi Yan wrote:
> >> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
> >> > There're some random failure for split_huge_page_test when khugepaged
> >> > collapses pages into pmd again which had split by the test.
> >> >
> >> > Prevent the khugepaged's collapses for split page by setting the
> >> > mapped pmd-huge-page with MADV_NOHUGEPAGE before split.
> >> 
> >> Why not disable khugepaged using APIs from hugepage_setting.h?
> >
> > Well, this also works with hugepage_save_settings() and write the
> > khugepaged/scan_sleep_millisecs with the maximum integer.
> >
> > I don't have a strong opinion but since it seems more hackish way to
> > change scan_sllep_millisecs, I use madvise() with MADV_NOHUGEPATE.
> >
> > Would it be better to change using APIs in hugepage_setting,h?
> 
> No. I did not realize there is no way of stopping khugepaged completely.
> 
> BTW, I am curious about your khugepaged config causing this issue.
> IIRC, khugepaged scan interval is about minutes and
> the time between madvise(MADV_HUGEPAGE) and the second
> is_backed_by_folio() should not be that long.

Yes. it's relly timing sensitive and I've failed to reproduce in the
real hardware. but in the emulation environment it often failed with 
the scan_sllep_millisecs as 10 seconds while the test running.

> 
> For your patch, maybe you want to check the return value of madvise() to
> make sure it succeeds.

Yeap. but it seems enough just worning message for the madvise() with
MADV_NOHUGEPAGE.

> 
> Otherwise,
> 
> feel free to add
> 
> Reviewed-by: Zi Yan <ziy@nvidia.com>

Thanks!

-- 
Sincerely,
Yeoreum Yun

Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Zi Yan]

On Thu Aug 20, 2026 at 5:26 PM EDT, Yeoreum Yun wrote:
>> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
>> > Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
>> > glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
>> > made by memalign().

I just googled the commit and find that Dev did that. ;)

>> >
>> > The underlying VMA may start at a different address from the aligned
>> > address returned by memalign(). Furthermore, a subsequent
>> > madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
>> > already set.
>> >
>> > This causes split_huge_page_test to fail because the check_huge_xxx()
>> > helpers incorrectly require the address returned by memalign() to
>> > match the VMA start address reported in /proc/self/smaps.
>> >
>> > Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
>> > /proc/self/smaps to detect huge pages and change the meaning of
>> > check_huge_xxx()'s nr_hpages argument:
>> 
>> Have you checked Baolin's patches[1] in mm-new? They resue
>> gather_after_split_folio_orders() to reimplement check_huge_xxx(), also
>> based on pagemap and kpageflags. Does it fix the issue?
>> 
>> [1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com/
>>
>
> Unfortunately, No. since __check_pmd_huge() in check_huge_xxx() still use
> /proc/self/smaps [1] for pmd THP, it still has problem though ths patch
> series applied.
>
> [1] https://lore.kernel.org/all/56b16691f605426b33b5cf47319233de6127a6b3.1785985999.git.baolin.wang@linux.alibaba.com/

In that case, is it possible to use and extend check_large_folios() for
all check_huge_xxx()? You still need pagemap_scan_get_categories() to
check PAGE_IS_HUGE to identify huge mappings. Or at least
check_huge_xxx() in your patch can share most of the code.

BTW, in your check_huge_shmem(), expect_huge seems to be inverted
compared to other check_huge_xxx().

-- 
Best Regards,
Yan, Zi

Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Yeoreum Yun]

On Thu, Aug 20, 2026 at 08:09:12PM -0400, Zi Yan wrote:
> On Thu Aug 20, 2026 at 5:26 PM EDT, Yeoreum Yun wrote:
> >> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
> >> > Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
> >> > glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
> >> > made by memalign().
> 
> I just googled the commit and find that Dev did that. ;)
> 
> >> >
> >> > The underlying VMA may start at a different address from the aligned
> >> > address returned by memalign(). Furthermore, a subsequent
> >> > madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
> >> > already set.
> >> >
> >> > This causes split_huge_page_test to fail because the check_huge_xxx()
> >> > helpers incorrectly require the address returned by memalign() to
> >> > match the VMA start address reported in /proc/self/smaps.
> >> >
> >> > Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
> >> > /proc/self/smaps to detect huge pages and change the meaning of
> >> > check_huge_xxx()'s nr_hpages argument:
> >> 
> >> Have you checked Baolin's patches[1] in mm-new? They resue
> >> gather_after_split_folio_orders() to reimplement check_huge_xxx(), also
> >> based on pagemap and kpageflags. Does it fix the issue?
> >> 
> >> [1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com/
> >>
> >
> > Unfortunately, No. since __check_pmd_huge() in check_huge_xxx() still use
> > /proc/self/smaps [1] for pmd THP, it still has problem though ths patch
> > series applied.
> >
> > [1] https://lore.kernel.org/all/56b16691f605426b33b5cf47319233de6127a6b3.1785985999.git.baolin.wang@linux.alibaba.com/
> 
> In that case, is it possible to use and extend check_large_folios() for
> all check_huge_xxx()? You still need pagemap_scan_get_categories() to
> check PAGE_IS_HUGE to identify huge mappings. Or at least
> check_huge_xxx() in your patch can share most of the code.

Agree. but TBH, I think check_large_folios() can replace checking
PAGE_IS_HUGE and keep the later part to check wehther PAGE_IS_FILE
and SWAPBACKED according to check_huge_xxx().

BTW, Should I do this after [1] is merged into mm-unstable?

> BTW, in your check_huge_shmem(), expect_huge seems to be inverted
> compared to other check_huge_xxx().

Yes. I've noticed. this was my typo while I change the variable name...

Thanks!

[1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com/


> 
> -- 
> Best Regards,
> Yan, Zi
> 

-- 
Sincerely,
Yeoreum Yun

Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Baolin Wang]

On 8/21/26 8:26 AM, Yeoreum Yun wrote:
> On Thu, Aug 20, 2026 at 08:09:12PM -0400, Zi Yan wrote:
>> On Thu Aug 20, 2026 at 5:26 PM EDT, Yeoreum Yun wrote:
>>>> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
>>>>> Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
>>>>> glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
>>>>> made by memalign().
>>
>> I just googled the commit and find that Dev did that. ;)
>>
>>>>>
>>>>> The underlying VMA may start at a different address from the aligned
>>>>> address returned by memalign(). Furthermore, a subsequent
>>>>> madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
>>>>> already set.
>>>>>
>>>>> This causes split_huge_page_test to fail because the check_huge_xxx()
>>>>> helpers incorrectly require the address returned by memalign() to
>>>>> match the VMA start address reported in /proc/self/smaps.
>>>>>
>>>>> Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
>>>>> /proc/self/smaps to detect huge pages and change the meaning of
>>>>> check_huge_xxx()'s nr_hpages argument:
>>>>
>>>> Have you checked Baolin's patches[1] in mm-new? They resue
>>>> gather_after_split_folio_orders() to reimplement check_huge_xxx(), also
>>>> based on pagemap and kpageflags. Does it fix the issue?
>>>>
>>>> [1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com/
>>>>
>>>
>>> Unfortunately, No. since __check_pmd_huge() in check_huge_xxx() still use
>>> /proc/self/smaps [1] for pmd THP, it still has problem though ths patch
>>> series applied.
>>>
>>> [1] https://lore.kernel.org/all/56b16691f605426b33b5cf47319233de6127a6b3.1785985999.git.baolin.wang@linux.alibaba.com/
>>
>> In that case, is it possible to use and extend check_large_folios() for
>> all check_huge_xxx()? You still need pagemap_scan_get_categories() to
>> check PAGE_IS_HUGE to identify huge mappings. Or at least
>> check_huge_xxx() in your patch can share most of the code.
> 
> Agree. but TBH, I think check_large_folios() can replace checking
> PAGE_IS_HUGE and keep the later part to check wehther PAGE_IS_FILE
> and SWAPBACKED according to check_huge_xxx().
> 
> BTW, Should I do this after [1] is merged into mm-unstable?

This series is already in mm-unstable, please rebase your patchset on 
mm-unstable branch. Moreover, we've extended check_huge_xxx() to support 
mTHP, so I don't think you need to change the meaning of 'nr_hpages' 
argument.

Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Zi Yan]

On Thu Aug 20, 2026 at 8:26 PM EDT, Yeoreum Yun wrote:
> On Thu, Aug 20, 2026 at 08:09:12PM -0400, Zi Yan wrote:
>> On Thu Aug 20, 2026 at 5:26 PM EDT, Yeoreum Yun wrote:
>> >> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
>> >> > Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
>> >> > glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
>> >> > made by memalign().
>> 
>> I just googled the commit and find that Dev did that. ;)
>> 
>> >> >
>> >> > The underlying VMA may start at a different address from the aligned
>> >> > address returned by memalign(). Furthermore, a subsequent
>> >> > madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
>> >> > already set.
>> >> >
>> >> > This causes split_huge_page_test to fail because the check_huge_xxx()
>> >> > helpers incorrectly require the address returned by memalign() to
>> >> > match the VMA start address reported in /proc/self/smaps.
>> >> >
>> >> > Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
>> >> > /proc/self/smaps to detect huge pages and change the meaning of
>> >> > check_huge_xxx()'s nr_hpages argument:
>> >> 
>> >> Have you checked Baolin's patches[1] in mm-new? They resue
>> >> gather_after_split_folio_orders() to reimplement check_huge_xxx(), also
>> >> based on pagemap and kpageflags. Does it fix the issue?
>> >> 
>> >> [1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com/
>> >>
>> >
>> > Unfortunately, No. since __check_pmd_huge() in check_huge_xxx() still use
>> > /proc/self/smaps [1] for pmd THP, it still has problem though ths patch
>> > series applied.
>> >
>> > [1] https://lore.kernel.org/all/56b16691f605426b33b5cf47319233de6127a6b3.1785985999.git.baolin.wang@linux.alibaba.com/
>> 
>> In that case, is it possible to use and extend check_large_folios() for
>> all check_huge_xxx()? You still need pagemap_scan_get_categories() to
>> check PAGE_IS_HUGE to identify huge mappings. Or at least
>> check_huge_xxx() in your patch can share most of the code.
>
> Agree. but TBH, I think check_large_folios() can replace checking
> PAGE_IS_HUGE and keep the later part to check wehther PAGE_IS_FILE

IIUC, PAGE_IS_HUGE comes from checking page table entry (see
pagemap_thp_category()), whereas check_large_folios() checks folios,
namely physical memory. A PTE-mapped order-9 (4KB base page) folio is
!PAGE_IS_HUGE but check_large_folios() returns true for PMD_SIZE.
check_huge_xxx() are checking PMD-mapped folios, so PAGE_IS_HUGE is
functionally equivalent.

> and SWAPBACKED according to check_huge_xxx().
>


-- 
Best Regards,
Yan, Zi