+ selftests-mm-check-after-split-folio-orders-in-split_huge_page_test.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: selftests/mm: check after-split folio orders in split_huge_page_test.
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-check-after-split-folio-orders-in-split_huge_page_test.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-check-after-split-folio-orders-in-split_huge_page_test.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Zi Yan <ziy@nvidia.com>
Subject: selftests/mm: check after-split folio orders in split_huge_page_test.
Date: Mon, 18 Aug 2025 14:46:22 -0400

Instead of just checking the existence of PMD folios before and after folio
split tests, use check_folio_orders() to check after-split folio orders.

The split ranges in split_thp_in_pagecache_to_order_at() are changed to
[addr, addr + pagesize) for every pmd_pagesize. It prevents folios within
the range being split multiple times due to debugfs split function always
perform splits with a pagesize step for a given range.

The following tests are not changed:
1. split_pte_mapped_thp: the test already uses kpageflags to check;
2. split_file_backed_thp: no vaddr available.

Link: https://lkml.kernel.org/r/20250818184622.1521620-6-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Donet Tom <donettom@linux.ibm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: wang lian <lianux.mm@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/split_huge_page_test.c |   88 ++++++++----
 1 file changed, 64 insertions(+), 24 deletions(-)

--- a/tools/testing/selftests/mm/split_huge_page_test.c~selftests-mm-check-after-split-folio-orders-in-split_huge_page_test
+++ a/tools/testing/selftests/mm/split_huge_page_test.c
@@ -26,6 +26,7 @@ uint64_t pagesize;
 unsigned int pageshift;
 uint64_t pmd_pagesize;
 unsigned int pmd_order;
+int *expected_orders;
 
 #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
 #define SMAP_PATH "/proc/self/smaps"
@@ -35,6 +36,11 @@ unsigned int pmd_order;
 #define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
 #define PATH_FMT "%s,0x%lx,0x%lx,%d"
 
+const char *pagemap_proc = "/proc/self/pagemap";
+const char *kpageflags_proc = "/proc/kpageflags";
+int pagemap_fd;
+int kpageflags_fd;
+
 static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
 		int kpageflags_fd)
 {
@@ -366,6 +372,13 @@ static void split_pmd_thp_to_order(int o
 		if (one_page[i] != (char)i)
 			ksft_exit_fail_msg("%ld byte corrupted\n", i);
 
+	memset(expected_orders, 0, sizeof(int) * (pmd_order + 1));
+	expected_orders[order] = 4 << (pmd_order - order);
+
+	if (check_after_split_folio_orders(one_page, len, pagemap_fd,
+					   kpageflags_fd, expected_orders,
+					   (pmd_order + 1)))
+		ksft_exit_fail_msg("Unexpected THP split\n");
 
 	if (!check_huge_anon(one_page, 0, pmd_pagesize))
 		ksft_exit_fail_msg("Still AnonHugePages not split\n");
@@ -380,22 +393,6 @@ static void split_pte_mapped_thp(void)
 	size_t len = 4 * pmd_pagesize;
 	uint64_t thp_size;
 	size_t i;
-	const char *pagemap_template = "/proc/%d/pagemap";
-	const char *kpageflags_proc = "/proc/kpageflags";
-	char pagemap_proc[255];
-	int pagemap_fd;
-	int kpageflags_fd;
-
-	if (snprintf(pagemap_proc, 255, pagemap_template, getpid()) < 0)
-		ksft_exit_fail_msg("get pagemap proc error: %s\n", strerror(errno));
-
-	pagemap_fd = open(pagemap_proc, O_RDONLY);
-	if (pagemap_fd == -1)
-		ksft_exit_fail_msg("read pagemap: %s\n", strerror(errno));
-
-	kpageflags_fd = open(kpageflags_proc, O_RDONLY);
-	if (kpageflags_fd == -1)
-		ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
 
 	one_page = mmap((void *)(1UL << 30), len, PROT_READ | PROT_WRITE,
 			MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
@@ -453,8 +450,6 @@ static void split_pte_mapped_thp(void)
 
 	ksft_test_result_pass("Split PTE-mapped huge pages successful\n");
 	munmap(one_page, len);
-	close(pagemap_fd);
-	close(kpageflags_fd);
 }
 
 static void split_file_backed_thp(int order)
@@ -657,6 +652,7 @@ static void split_thp_in_pagecache_to_or
 		const char *fs_loc, int order, int offset)
 {
 	int fd;
+	char *split_addr;
 	char *addr;
 	size_t i;
 	char testfile[INPUT_MAX];
@@ -670,14 +666,33 @@ static void split_thp_in_pagecache_to_or
 	err = create_pagecache_thp_and_fd(testfile, fd_size, &fd, &addr);
 	if (err)
 		return;
+
 	err = 0;
 
-	if (offset == -1)
-		write_debugfs(PID_FMT, getpid(), (uint64_t)addr,
-			      (uint64_t)addr + fd_size, order);
-	else
-		write_debugfs(PID_FMT_OFFSET, getpid(), (uint64_t)addr,
-			      (uint64_t)addr + fd_size, order, offset);
+	memset(expected_orders, 0, sizeof(int) * (pmd_order + 1));
+	/*
+	 * use [split_addr, split_addr + pagesize) range to split THPs, since
+	 * the debugfs function always split a range with pagesize step and
+	 * providing a full [addr, addr + fd_size) range can trigger multiple
+	 * splits, complicating after-split result checking.
+	 */
+	if (offset == -1) {
+		for (split_addr = addr; split_addr < addr + fd_size; split_addr += pmd_pagesize)
+			write_debugfs(PID_FMT, getpid(), (uint64_t)split_addr,
+				      (uint64_t)split_addr + pagesize, order);
+
+		expected_orders[order] = fd_size / (pagesize << order);
+	} else {
+		int times = fd_size / pmd_pagesize;
+
+		for (split_addr = addr; split_addr < addr + fd_size; split_addr += pmd_pagesize)
+			write_debugfs(PID_FMT_OFFSET, getpid(), (uint64_t)split_addr,
+				      (uint64_t)split_addr + pagesize, order, offset);
+
+		for (i = order + 1; i < pmd_order; i++)
+			expected_orders[i] = times;
+		expected_orders[order] = 2 * times;
+	}
 
 	for (i = 0; i < fd_size; i++)
 		if (*(addr + i) != (char)i) {
@@ -686,6 +701,14 @@ static void split_thp_in_pagecache_to_or
 			goto out;
 		}
 
+	if (check_after_split_folio_orders(addr, fd_size, pagemap_fd,
+					   kpageflags_fd, expected_orders,
+					   (pmd_order + 1))) {
+		ksft_print_msg("Unexpected THP split\n");
+		err = 1;
+		goto out;
+	}
+
 	if (!check_huge_file(addr, 0, pmd_pagesize)) {
 		ksft_print_msg("Still FilePmdMapped not split\n");
 		err = EXIT_FAILURE;
@@ -737,9 +760,22 @@ int main(int argc, char **argv)
 
 	nr_pages = pmd_pagesize / pagesize;
 	pmd_order = sz2ord(pmd_pagesize, pagesize);
+
+	expected_orders = (int *)malloc(sizeof(int) * (pmd_order + 1));
+	if (!expected_orders)
+		ksft_exit_fail_msg("Fail to allocate memory: %s\n", strerror(errno));
+
 	tests = 2 + (pmd_order - 1) + (2 * pmd_order) + (pmd_order - 1) * 4 + 2;
 	ksft_set_plan(tests);
 
+	pagemap_fd = open(pagemap_proc, O_RDONLY);
+	if (pagemap_fd == -1)
+		ksft_exit_fail_msg("read pagemap: %s\n", strerror(errno));
+
+	kpageflags_fd = open(kpageflags_proc, O_RDONLY);
+	if (kpageflags_fd == -1)
+		ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
+
 	fd_size = 2 * pmd_pagesize;
 
 	split_pmd_zero_pages();
@@ -764,6 +800,10 @@ int main(int argc, char **argv)
 			split_thp_in_pagecache_to_order_at(fd_size, fs_loc, i, offset);
 	cleanup_thp_fs(fs_loc, created_tmp);
 
+	close(pagemap_fd);
+	close(kpageflags_fd);
+	free(expected_orders);
+
 	ksft_finished();
 
 	return 0;
_

Patches currently in -mm which might be from ziy@nvidia.com are

selftests-mm-fix-force_read-to-read-input-value-correctly.patch
mm-huge_memory-add-new_order-and-offset-to-split_huge_pages-pr_debug.patch
selftests-mm-mark-all-functions-static-in-split_huge_page_testc.patch
selftests-mm-reimplement-is_backed_by_thp-with-more-precise-check.patch
selftests-mm-add-check_after_split_folio_orders-helper.patch
selftests-mm-check-after-split-folio-orders-in-split_huge_page_test.patch