[PATCH v2 2/8] ext4: make regular file's buffered write path support large folios

Zhang Yi
2025-05-12T06:44:54Z

From: Zhang Yi <yi.zhang@huawei.com>

The current buffered write path in ext4 can only allocate and handle
folios of PAGE_SIZE size. To support larger folios, modify
ext4_da_write_begin() and ext4_write_begin() to allocate higher-order
folios, and trim the write length if it exceeds the folio size.
Additionally, in ext4_da_do_write_end(), use offset_in_folio() instead
of PAGE_SIZE.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
fs/ext4/inode.c | 31 +++++++++++++++++++++----------
1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 94c7d2d828a6..4d8187f3814e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1027,7 +1027,7 @@ int ext4_block_write_begin(handle_t *handle, struct folio *folio,
loff_t pos, unsigned len,
get_block_t *get_block)
{
- unsigned from = pos & (PAGE_SIZE - 1);
+ unsigned int from = offset_in_folio(folio, pos);
unsigned to = from + len;
struct inode *inode = folio->mapping->host;
unsigned block_start, block_end;
@@ -1041,8 +1041,7 @@ int ext4_block_write_begin(handle_t *handle, struct folio *folio,
bool should_journal_data = ext4_should_journal_data(inode);

BUG_ON(!folio_test_locked(folio));
- BUG_ON(from > PAGE_SIZE);
- BUG_ON(to > PAGE_SIZE);
+ BUG_ON(to > folio_size(folio));
BUG_ON(from > to);

head = folio_buffers(folio);
@@ -1152,6 +1151,7 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
struct folio *folio;
pgoff_t index;
unsigned from, to;
+ fgf_t fgp = FGP_WRITEBEGIN;

ret = ext4_emergency_state(inode->i_sb);
if (unlikely(ret))
@@ -1164,8 +1164,6 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
*/
needed_blocks = ext4_writepage_trans_blocks(inode) + 1;
index = pos >> PAGE_SHIFT;
- from = pos & (PAGE_SIZE - 1);
- to = from + len;

if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) {
ret = ext4_try_to_write_inline_data(mapping, inode, pos, len,
@@ -1184,10 +1182,18 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
* the folio (if needed) without using GFP_NOFS.
*/
retry_grab:
- folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
- mapping_gfp_mask(mapping));
+ fgp |= fgf_set_order(len);
+ folio = __filemap_get_folio(mapping, index, fgp,
+ mapping_gfp_mask(mapping));
if (IS_ERR(folio))
return PTR_ERR(folio);
+
+ if (pos + len > folio_pos(folio) + folio_size(folio))
+ len = folio_pos(folio) + folio_size(folio) - pos;
+
+ from = offset_in_folio(folio, pos);
+ to = from + len;
+
/*
* The same as page allocation, we prealloc buffer heads before
* starting the handle.
@@ -2920,6 +2926,7 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
struct folio *folio;
pgoff_t index;
struct inode *inode = mapping->host;
+ fgf_t fgp = FGP_WRITEBEGIN;

ret = ext4_emergency_state(inode->i_sb);
if (unlikely(ret))
@@ -2945,11 +2952,15 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
}

retry:
- folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
- mapping_gfp_mask(mapping));
+ fgp |= fgf_set_order(len);
+ folio = __filemap_get_folio(mapping, index, fgp,
+ mapping_gfp_mask(mapping));
if (IS_ERR(folio))
return PTR_ERR(folio);

+ if (pos + len > folio_pos(folio) + folio_size(folio))
+ len = folio_pos(folio) + folio_size(folio) - pos;
+
ret = ext4_block_write_begin(NULL, folio, pos, len,
ext4_da_get_block_prep);
if (ret < 0) {
@@ -3038,7 +3049,7 @@ static int ext4_da_do_write_end(struct address_space *mapping,
unsigned long end;

i_size_write(inode, new_i_size);
- end = (new_i_size - 1) & (PAGE_SIZE - 1);
+ end = offset_in_folio(folio, new_i_size - 1);
if (copied && ext4_da_should_update_i_disksize(folio, end)) {
ext4_update_i_disksize(inode, new_i_size);
disksize_changed = true;
--
2.46.1