[PATCH -next] tmpfs: fault in smaller chunks if large folio allocation not allowed

[Kefeng Wang <wangkefeng.wang@huawei.com>]

The tmpfs supports large folio, but there is some configurable options
to enable/disable large folio allocation, and for huge=within_size,
large folio only allowabled if it fully within i_size, so there is
performance issue when perform write without large folio, the issue is
similar to commit 4e527d5841e2 ("iomap: fault in smaller chunks for
non-large folio mappings").

Fix it by checking whether it allows large folio allocation or not
before perform write.

Fixes: 9aac777aaf94 ("filemap: Convert generic_perform_write() to support large folios")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 include/linux/fs.h | 2 ++
 mm/filemap.c       | 7 ++++++-
 mm/shmem.c         | 5 +++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1e25267e2e48..d642e323354b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -346,6 +346,8 @@ struct readahead_control;
 #define IOCB_DIO_CALLER_COMP	(1 << 22)
 /* kiocb is a read or write operation submitted by fs/aio.c. */
 #define IOCB_AIO_RW		(1 << 23)
+/* fault int small chunks(PAGE_SIZE) from userspace */
+#define IOCB_NO_LARGE_CHUNK	(1 << 24)
 
 /* for use in trace events */
 #define TRACE_IOCB_STRINGS \
diff --git a/mm/filemap.c b/mm/filemap.c
index 3e46ca45e13d..27e73f2680ef 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4132,9 +4132,14 @@ ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
 	loff_t pos = iocb->ki_pos;
 	struct address_space *mapping = file->f_mapping;
 	const struct address_space_operations *a_ops = mapping->a_ops;
-	size_t chunk = mapping_max_folio_size(mapping);
 	long status = 0;
 	ssize_t written = 0;
+	size_t chunk;
+
+	if (iocb->ki_flags & IOCB_NO_LARGE_CHUNK)
+		chunk = PAGE_SIZE;
+	else
+		chunk = mapping_max_folio_size(mapping);
 
 	do {
 		struct folio *folio;
diff --git a/mm/shmem.c b/mm/shmem.c
index 530fe8cfcc21..2909bead774b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3228,6 +3228,7 @@ static ssize_t shmem_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file->f_mapping->host;
+	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
 	ssize_t ret;
 
 	inode_lock(inode);
@@ -3240,6 +3241,10 @@ static ssize_t shmem_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	ret = file_update_time(file);
 	if (ret)
 		goto unlock;
+
+	if (!shmem_allowable_huge_orders(inode, NULL, index, 0, false))
+		iocb->ki_flags |= IOCB_NO_LARGE_CHUNK;
+
 	ret = generic_perform_write(iocb, from);
 unlock:
 	inode_unlock(inode);
-- 
2.27.0