[PATCH v4 06/15] selftests/mm: size tmpfs according to PMD page size in split_huge_page_test

Sayali Patil
2026-04-06T09:20:39Z

The split_file_backed_thp() test mounts a tmpfs with a fixed size of
"4m". This works on systems with smaller PMD page sizes,
but fails on configurations where the PMD huge page size is
larger (e.g. 16MB).

On such systems, the fixed 4MB tmpfs is insufficient to allocate even
a single PMD-sized THP, causing the test to fail.

Fix this by sizing the tmpfs dynamically based on the runtime
pmd_pagesize, allocating space for two PMD-sized pages.

Before patch:
running ./split_huge_page_test /tmp/xfs_dir_YTrI5E
--------------------------------------------------
TAP version 13
1..55
ok 1 Split zero filled huge pages successful
ok 2 Split huge pages to order 0 successful
ok 3 Split huge pages to order 2 successful
ok 4 Split huge pages to order 3 successful
ok 5 Split huge pages to order 4 successful
ok 6 Split huge pages to order 5 successful
ok 7 Split huge pages to order 6 successful
ok 8 Split huge pages to order 7 successful
ok 9 Split PTE-mapped huge pages successful
Please enable pr_debug in split_huge_pages_in_file() for more info.
Failed to write data to testing file: Success (0)
Bail out! Error occurred
Planned tests != run tests (55 != 9)
Totals: pass:9 fail:0 xfail:0 xpass:0 skip:0 error:0
[FAIL]

After patch:
running ./split_huge_page_test /tmp/xfs_dir_bMvj6o
--------------------------------------------------
TAP version 13
1..55
ok 1 Split zero filled huge pages successful
ok 2 Split huge pages to order 0 successful
ok 3 Split huge pages to order 2 successful
ok 4 Split huge pages to order 3 successful
ok 5 Split huge pages to order 4 successful
ok 6 Split huge pages to order 5 successful
ok 7 Split huge pages to order 6 successful
ok 8 Split huge pages to order 7 successful
ok 9 Split PTE-mapped huge pages successful
Please enable pr_debug in split_huge_pages_in_file() for more info.
Please check dmesg for more information
ok 10 File-backed THP split to order 0 test done
Please enable pr_debug in split_huge_pages_in_file() for more info.
Please check dmesg for more information
ok 11 File-backed THP split to order 1 test done
Please enable pr_debug in split_huge_pages_in_file() for more info.
Please check dmesg for more information
ok 12 File-backed THP split to order 2 test done
...
ok 55 Split PMD-mapped pagecache folio to order 7 at
in-folio offset 128 passed
Totals: pass:55 fail:0 xfail:0 xpass:0 skip:0 error:0
[PASS]
ok 1 split_huge_page_test /tmp/xfs_dir_bMvj6o

Fixes: fbe37501b252 ("mm: huge_memory: debugfs for file-backed THP split")
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
---
tools/testing/selftests/mm/split_huge_page_test.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index e0167111bdd1..57e8a1c9647a 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -484,6 +484,8 @@ static void split_file_backed_thp(int order)
char tmpfs_template[] = "/tmp/thp_split_XXXXXX";
const char *tmpfs_loc = mkdtemp(tmpfs_template);
char testfile[INPUT_MAX];
+ unsigned long size = 2 * pmd_pagesize;
+ char opts[64];
ssize_t num_written, num_read;
char *file_buf1, *file_buf2;
uint64_t pgoff_start = 0, pgoff_end = 1024;
@@ -503,7 +505,8 @@ static void split_file_backed_thp(int order)
file_buf1[i] = (char)i;
memset(file_buf2, 0, pmd_pagesize);

- status = mount("tmpfs", tmpfs_loc, "tmpfs", 0, "huge=always,size=4m");
+ snprintf(opts, sizeof(opts), "huge=always,size=%lu", size);
+ status = mount("tmpfs", tmpfs_loc, "tmpfs", 0, opts);

if (status)
ksft_exit_fail_msg("Unable to create a tmpfs for testing\n");
--
2.52.0