[PATCH v2 1/3] selftests/mm: make file-backed THP split work by writing PMD size data

[PATCH v2 1/3] selftests/mm: make file-backed THP split work by writing PMD size data

[Zi Yan]

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.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
V1 -> V2: write PMD size data instead of setting
          /sys/kernel/mm/transparent_hugepage/shmem_enabled to "force".

 .../selftests/mm/split_huge_page_test.c       | 52 ++++++++++++++++---
 1 file changed, 44 insertions(+), 8 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..ba498aaaf857 100644
--- 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");
 }
 
-- 
2.45.2

[PATCH v2 2/3] mm/huge_memory: allow split shmem large folio to any lower order

[Zi Yan]

Commit 4d684b5f92ba ("mm: shmem: add large folio support for tmpfs") has
added large folio support to shmem. Remove the restriction in
split_huge_page*().

Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/huge_memory.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 3d3ebdc002d5..deb4e72daeb9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3299,7 +3299,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 		/* Some pages can be beyond EOF: drop them from page cache */
 		if (tail->index >= end) {
 			if (shmem_mapping(folio->mapping))
-				nr_dropped++;
+				nr_dropped += new_nr;
 			else if (folio_test_clear_dirty(tail))
 				folio_account_cleaned(tail,
 					inode_to_wb(folio->mapping->host));
@@ -3465,12 +3465,6 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 			return -EINVAL;
 		}
 	} else if (new_order) {
-		/* Split shmem folio to non-zero order not supported */
-		if (shmem_mapping(folio->mapping)) {
-			VM_WARN_ONCE(1,
-				"Cannot split shmem folio to non-0 order");
-			return -EINVAL;
-		}
 		/*
 		 * No split if the file system does not support large folio.
 		 * Note that we might still have THPs in such mappings due to
-- 
2.45.2

[PATCH v2 3/3] selftests/mm: test splitting file-backed THP to any lower order.

[Zi Yan]

Now split_huge_page*() supports shmem THP split to any lower order.
Test it.

The test now reads file content out after split to check if the split
corrupts the file data.

Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 tools/testing/selftests/mm/split_huge_page_test.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index ba498aaaf857..e0304046b1a0 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -261,7 +261,7 @@ void split_pte_mapped_thp(void)
 	close(kpageflags_fd);
 }
 
-void split_file_backed_thp(void)
+void split_file_backed_thp(int order)
 {
 	int status;
 	int fd;
@@ -313,7 +313,7 @@ void split_file_backed_thp(void)
 	}
 
 	/* split the file-backed THP */
-	write_debugfs(PATH_FMT, testfile, pgoff_start, pgoff_end, 0);
+	write_debugfs(PATH_FMT, testfile, pgoff_start, pgoff_end, order);
 
 	/* check file content after split */
 	status = lseek(fd, 0, SEEK_SET);
@@ -351,7 +351,7 @@ void split_file_backed_thp(void)
 		ksft_exit_fail_msg("cannot remove tmp dir: %s\n", strerror(errno));
 
 	ksft_print_msg("Please check dmesg for more information\n");
-	ksft_test_result_pass("File-backed THP split test done\n");
+	ksft_test_result_pass("File-backed THP split to order %d test done\n", order);
 	return;
 
 close_file:
@@ -517,7 +517,7 @@ int main(int argc, char **argv)
 	if (argc > 1)
 		optional_xfs_path = argv[1];
 
-	ksft_set_plan(1+8+2+9);
+	ksft_set_plan(1+8+1+9+9);
 
 	pagesize = getpagesize();
 	pageshift = ffs(pagesize) - 1;
@@ -534,7 +534,8 @@ int main(int argc, char **argv)
 			split_pmd_thp_to_order(i);
 
 	split_pte_mapped_thp();
-	split_file_backed_thp();
+	for (i = 0; i < 9; i++)
+		split_file_backed_thp(i);
 
 	created_tmp = prepare_thp_fs(optional_xfs_path, fs_loc_template,
 			&fs_loc);
-- 
2.45.2

Re: [PATCH v2 2/3] mm/huge_memory: allow split shmem large folio to any lower order

[Yang Shi]

On 1/22/25 8:19 AM, Zi Yan wrote:
> Commit 4d684b5f92ba ("mm: shmem: add large folio support for tmpfs") has
> added large folio support to shmem. Remove the restriction in
> split_huge_page*().

Reviewed-by: Yang Shi <yang@os.amperecomputing.com>

>
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> ---
>   mm/huge_memory.c | 8 +-------
>   1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 3d3ebdc002d5..deb4e72daeb9 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3299,7 +3299,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>   		/* Some pages can be beyond EOF: drop them from page cache */
>   		if (tail->index >= end) {
>   			if (shmem_mapping(folio->mapping))
> -				nr_dropped++;
> +				nr_dropped += new_nr;
>   			else if (folio_test_clear_dirty(tail))
>   				folio_account_cleaned(tail,
>   					inode_to_wb(folio->mapping->host));
> @@ -3465,12 +3465,6 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>   			return -EINVAL;
>   		}
>   	} else if (new_order) {
> -		/* Split shmem folio to non-zero order not supported */
> -		if (shmem_mapping(folio->mapping)) {
> -			VM_WARN_ONCE(1,
> -				"Cannot split shmem folio to non-0 order");
> -			return -EINVAL;
> -		}
>   		/*
>   		 * No split if the file system does not support large folio.
>   		 * Note that we might still have THPs in such mappings due to