[PATCH v2 4/7] mm/selftests: Fix split_huge_page_test failure on systems with 64KB page size

[Aboorva Devarajan <aboorvad@linux.ibm.com>]

From: Donet Tom <donettom@linux.ibm.com>

The split_huge_page_test fails on systems with a 64KB base page size.
This is because the order of a 2MB huge page is different:

On 64KB systems, the order is 5.

On 4KB systems, it's 9.

The test currently assumes a maximum huge page order of 9, which is only
valid for 4KB base page systems. On systems with 64KB pages, attempting
to split huge pages beyond their actual order (5) causes the test to fail.

In this patch, we calculate the huge page order based on the system's base
page size. With this change, the tests now run successfully on both 64KB
and 4KB page size systems.

Fixes: fa6c02315f745 ("mm: huge_memory: a new debugfs interface for splitting THP tests")
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
---
 .../selftests/mm/split_huge_page_test.c       | 23 ++++++++++++++-----
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index aa7400ed0e99..38296a758330 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -514,6 +514,15 @@ void split_thp_in_pagecache_to_order_at(size_t fd_size, const char *fs_loc,
 	}
 }
 
+static unsigned int get_order(unsigned int pages)
+{
+	unsigned int order = 0;
+
+	while ((1U << order) < pages)
+		order++;
+	return order;
+}
+
 int main(int argc, char **argv)
 {
 	int i;
@@ -523,6 +532,7 @@ int main(int argc, char **argv)
 	const char *fs_loc;
 	bool created_tmp;
 	int offset;
+	unsigned int max_order;
 
 	ksft_print_header();
 
@@ -534,32 +544,33 @@ int main(int argc, char **argv)
 	if (argc > 1)
 		optional_xfs_path = argv[1];
 
-	ksft_set_plan(1+8+1+9+9+8*4+2);
-
 	pagesize = getpagesize();
 	pageshift = ffs(pagesize) - 1;
 	pmd_pagesize = read_pmd_pagesize();
 	if (!pmd_pagesize)
 		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
 
+	max_order = get_order(pmd_pagesize/pagesize);
+	ksft_set_plan(1+(max_order-1)+1+max_order+max_order+(max_order-1)*4+2);
+
 	fd_size = 2 * pmd_pagesize;
 
 	split_pmd_zero_pages();
 
-	for (i = 0; i < 9; i++)
+	for (i = 0; i < max_order; i++)
 		if (i != 1)
 			split_pmd_thp_to_order(i);
 
 	split_pte_mapped_thp();
-	for (i = 0; i < 9; i++)
+	for (i = 0; i < max_order; i++)
 		split_file_backed_thp(i);
 
 	created_tmp = prepare_thp_fs(optional_xfs_path, fs_loc_template,
 			&fs_loc);
-	for (i = 8; i >= 0; i--)
+	for (i = (max_order-1); i >= 0; i--)
 		split_thp_in_pagecache_to_order_at(fd_size, fs_loc, i, -1);
 
-	for (i = 0; i < 9; i++)
+	for (i = 0; i < max_order; i++)
 		for (offset = 0;
 		     offset < pmd_pagesize / pagesize;
 		     offset += MAX(pmd_pagesize / pagesize / 4, 1 << i))
-- 
2.43.5