[PATCH 1/3] selftests/mm: make file-backed THP split work by setting force option

[Zi Yan <ziy@xxxxxxxxxx>]

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.

Set /sys/kernel/mm/transparent_hugepage/shmem_enabled to "force" to force
THP allocation.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Tested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 .../selftests/mm/split_huge_page_test.c       | 48 +++++++++++++++++--
 1 file changed, 45 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 3f353f3d070f..8e15fc9dce3a 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -264,15 +264,46 @@ void split_pte_mapped_thp(void)
 void split_file_backed_thp(void)
 {
 	int status;
-	int fd;
-	ssize_t num_written;
+	int fd, shmem_sysctl_fd;
+	ssize_t num_written, num_read;
 	char tmpfs_template[] = "/tmp/thp_split_XXXXXX";
 	const char *tmpfs_loc = mkdtemp(tmpfs_template);
-	char testfile[INPUT_MAX];
+	char testfile[INPUT_MAX], sysctl_buf[INPUT_MAX] = {0};
 	uint64_t pgoff_start = 0, pgoff_end = 1024;
+	const char *shmem_sysctl = "/sys/kernel/mm/transparent_hugepage/shmem_enabled";
+	char *opt1, *opt2;
 
 	ksft_print_msg("Please enable pr_debug in split_huge_pages_in_file() for more info.\n");
 
+	shmem_sysctl_fd = open(shmem_sysctl, O_RDWR);
+	if (shmem_sysctl_fd == -1) {
+		ksft_perror("cannot open shmem sysctl");
+		goto out;
+	}
+
+	num_read = read(shmem_sysctl_fd, sysctl_buf, INPUT_MAX);
+	if (num_read < 1) {
+		ksft_perror("Failed to read shmem sysctl");
+		goto cleanup_sysctl;
+	}
+
+	opt1 = strchr(sysctl_buf, '[');
+	opt2 = strchr(sysctl_buf, ']');
+	if (!opt1 || !opt2) {
+		ksft_perror("cannot read shmem sysctl config");
+		goto cleanup_sysctl;
+	}
+
+	/* get existing shmem sysctl config into sysctl_buf */
+	strncpy(sysctl_buf, opt1 + 1, opt2 - opt1 - 1);
+	memset(sysctl_buf + (opt2 - opt1 - 1), 0, INPUT_MAX);
+
+	num_written = write(shmem_sysctl_fd, "force", sizeof("force"));
+	if (num_written < 1) {
+		ksft_perror("Fail to write force to shmem sysctl");
+		goto cleanup_sysctl;
+	}
+
 	status = mount("tmpfs", tmpfs_loc, "tmpfs", 0, "huge=always,size=4m");
 
 	if (status)
@@ -317,13 +348,24 @@ void split_file_backed_thp(void)
 	if (status)
 		ksft_exit_fail_msg("cannot remove tmp dir: %s\n", strerror(errno));
 
+	num_written = write(shmem_sysctl_fd, sysctl_buf, strlen(sysctl_buf) + 1);
+	if (num_written < 1)
+		ksft_perror("Fail to restore shmem sysctl");
+
+	close(shmem_sysctl_fd);
 	ksft_print_msg("Please check dmesg for more information\n");
 	ksft_test_result_pass("File-backed THP split test done\n");
 	return;
 
 cleanup:
+	num_written = write(shmem_sysctl_fd, sysctl_buf, strlen(sysctl_buf) + 1);
+	if (num_written < 1)
+		ksft_perror("Fail to restore shmem sysctl");
 	umount(tmpfs_loc);
 	rmdir(tmpfs_loc);
+cleanup_sysctl:
+	close(shmem_sysctl_fd);
+out:
 	ksft_exit_fail_msg("Error occurred\n");
 }
 
-- 
2.45.2