[PATCH v2 1/8] ext4: make ext4_mpage_readpages() support large folios

Zhang Yi
2025-05-12T06:44:51Z

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

ext4_mpage_readpages() currently assumes that each folio is the size of
PAGE_SIZE. Modify it to atomically calculate the number of blocks per
folio and iterate through the blocks in each folio, which would allow
for support of larger folios.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
fs/ext4/readpage.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index 5d3a9dc9a32d..f329daf6e5c7 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -227,24 +227,30 @@ int ext4_mpage_readpages(struct inode *inode,
int length;
unsigned relative_block = 0;
struct ext4_map_blocks map;
- unsigned int nr_pages = rac ? readahead_count(rac) : 1;
+ unsigned int nr_pages, folio_pages;

map.m_pblk = 0;
map.m_lblk = 0;
map.m_len = 0;
map.m_flags = 0;

- for (; nr_pages; nr_pages--) {
+ nr_pages = rac ? readahead_count(rac) : folio_nr_pages(folio);
+ for (; nr_pages; nr_pages -= folio_pages) {
int fully_mapped = 1;
- unsigned first_hole = blocks_per_page;
+ unsigned int first_hole;
+ unsigned int blocks_per_folio;

if (rac)
folio = readahead_folio(rac);
+
+ folio_pages = folio_nr_pages(folio);
prefetchw(&folio->flags);

if (folio_buffers(folio))
goto confused;

+ blocks_per_folio = folio_size(folio) >> blkbits;
+ first_hole = blocks_per_folio;
block_in_file = next_block =
(sector_t)folio->index << (PAGE_SHIFT - blkbits);
last_block = block_in_file + nr_pages * blocks_per_page;
@@ -270,7 +276,7 @@ int ext4_mpage_readpages(struct inode *inode,
map.m_flags &= ~EXT4_MAP_MAPPED;
break;
}
- if (page_block == blocks_per_page)
+ if (page_block == blocks_per_folio)
break;
page_block++;
block_in_file++;
@@ -281,7 +287,7 @@ int ext4_mpage_readpages(struct inode *inode,
* Then do more ext4_map_blocks() calls until we are
* done with this folio.
*/
- while (page_block < blocks_per_page) {
+ while (page_block < blocks_per_folio) {
if (block_in_file < last_block) {
map.m_lblk = block_in_file;
map.m_len = last_block - block_in_file;
@@ -296,13 +302,13 @@ int ext4_mpage_readpages(struct inode *inode,
}
if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
fully_mapped = 0;
- if (first_hole == blocks_per_page)
+ if (first_hole == blocks_per_folio)
first_hole = page_block;
page_block++;
block_in_file++;
continue;
}
- if (first_hole != blocks_per_page)
+ if (first_hole != blocks_per_folio)
goto confused; /* hole -> non-hole */

/* Contiguous blocks? */
@@ -315,13 +321,13 @@ int ext4_mpage_readpages(struct inode *inode,
/* needed? */
map.m_flags &= ~EXT4_MAP_MAPPED;
break;
- } else if (page_block == blocks_per_page)
+ } else if (page_block == blocks_per_folio)
break;
page_block++;
block_in_file++;
}
}
- if (first_hole != blocks_per_page) {
+ if (first_hole != blocks_per_folio) {
folio_zero_segment(folio, first_hole << blkbits,
folio_size(folio));
if (first_hole == 0) {
@@ -367,11 +373,11 @@ int ext4_mpage_readpages(struct inode *inode,

if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
(relative_block == map.m_len)) ||
- (first_hole != blocks_per_page)) {
+ (first_hole != blocks_per_folio)) {
submit_bio(bio);
bio = NULL;
} else
- last_block_in_bio = first_block + blocks_per_page - 1;
+ last_block_in_bio = first_block + blocks_per_folio - 1;
continue;
confused:
if (bio) {
--
2.46.1