selftests/mm: make file-backed THP split work by writing PMD size data

Commit acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs")
changes huge=always to allocate THP/mTHP based on write size and
split_huge_page_test does not write PMD size data, so file-back THP is not
created during the test.  Fix it by writing PMD size data.

Link: https://lkml.kernel.org/r/20250122161928.1240637-1-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kirill A. Shuemov <kirill.shutemov@linux.intel.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 3f353f3d070fa133c77dd4bc83bcae3dfa91f83d..ba498aaaf857c7d263d9d6087744522855f42bf6 100644 (file)
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -265,14 +265,28 @@ void split_file_backed_thp(void)
 {
        int status;
        int fd;
-       ssize_t num_written;
        char tmpfs_template[] = "/tmp/thp_split_XXXXXX";
        const char *tmpfs_loc = mkdtemp(tmpfs_template);
        char testfile[INPUT_MAX];
+       ssize_t num_written, num_read;
+       char *file_buf1, *file_buf2;
        uint64_t pgoff_start = 0, pgoff_end = 1024;
+       int i;
 
        ksft_print_msg("Please enable pr_debug in split_huge_pages_in_file() for more info.\n");
 
+       file_buf1 = (char *)malloc(pmd_pagesize);
+       file_buf2 = (char *)malloc(pmd_pagesize);
+
+       if (!file_buf1 || !file_buf2) {
+               ksft_print_msg("cannot allocate file buffers\n");
+               goto out;
+       }
+
+       for (i = 0; i < pmd_pagesize; i++)
+               file_buf1[i] = (char)i;
+       memset(file_buf2, 0, pmd_pagesize);
+
        status = mount("tmpfs", tmpfs_loc, "tmpfs", 0, "huge=always,size=4m");
 
        if (status)
@@ -281,26 +295,45 @@ void split_file_backed_thp(void)
        status = snprintf(testfile, INPUT_MAX, "%s/thp_file", tmpfs_loc);
        if (status >= INPUT_MAX) {
                ksft_exit_fail_msg("Fail to create file-backed THP split testing file\n");
+               goto cleanup;
        }
 
-       fd = open(testfile, O_CREAT|O_WRONLY, 0664);
+       fd = open(testfile, O_CREAT|O_RDWR, 0664);
        if (fd == -1) {
                ksft_perror("Cannot open testing file");
                goto cleanup;
        }
 
-       /* write something to the file, so a file-backed THP can be allocated */
-       num_written = write(fd, tmpfs_loc, strlen(tmpfs_loc) + 1);
-       close(fd);
+       /* write pmd size data to the file, so a file-backed THP can be allocated */
+       num_written = write(fd, file_buf1, pmd_pagesize);
 
-       if (num_written < 1) {
-               ksft_perror("Fail to write data to testing file");
-               goto cleanup;
+       if (num_written == -1 || num_written != pmd_pagesize) {
+               ksft_perror("Failed to write data to testing file");
+               goto close_file;
        }
 
        /* split the file-backed THP */
        write_debugfs(PATH_FMT, testfile, pgoff_start, pgoff_end, 0);
 
+       /* check file content after split */
+       status = lseek(fd, 0, SEEK_SET);
+       if (status == -1) {
+               ksft_perror("Cannot lseek file");
+               goto close_file;
+       }
+
+       num_read = read(fd, file_buf2, num_written);
+       if (num_read == -1 || num_read != num_written) {
+               ksft_perror("Cannot read file content back");
+               goto close_file;
+       }
+
+       if (strncmp(file_buf1, file_buf2, pmd_pagesize) != 0) {
+               ksft_print_msg("File content changed\n");
+               goto close_file;
+       }
+
+       close(fd);
        status = unlink(testfile);
        if (status) {
                ksft_perror("Cannot remove testing file");
@@ -321,9 +354,12 @@ void split_file_backed_thp(void)
        ksft_test_result_pass("File-backed THP split test done\n");
        return;
 
+close_file:
+       close(fd);
 cleanup:
        umount(tmpfs_loc);
        rmdir(tmpfs_loc);
+out:
        ksft_exit_fail_msg("Error occurred\n");
 }