[PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

Pankaj Raghav (Samsung)
2025-08-14T14:21:45Z

From: Pankaj Raghav <p.raghav@samsung.com>

iomap_dio_zero() uses a custom allocated memory of zeroes for padding
zeroes. This was a temporary solution until there was a way to request a
zero folio that was greater than the PAGE_SIZE.

Use largest_zero_folio() function instead of using the custom allocated
memory of zeroes. There is no guarantee from largest_zero_folio()
function that it will always return a PMD sized folio. Adapt the code so
that it can also work if largest_zero_folio() returns a ZERO_PAGE.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
fs/iomap/direct-io.c | 38 +++++++++++++++-----------------------
1 file changed, 15 insertions(+), 23 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index b84f6af2eb4c..a7a281ea3e50 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -24,13 +24,6 @@
#define IOMAP_DIO_WRITE (1U << 30)
#define IOMAP_DIO_DIRTY (1U << 31)

-/*
- * Used for sub block zeroing in iomap_dio_zero()
- */
-#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
-#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
-static struct page *zero_page;
-
struct iomap_dio {
struct kiocb *iocb;
const struct iomap_dio_ops *dops;
@@ -285,24 +278,35 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
{
struct inode *inode = file_inode(dio->iocb->ki_filp);
struct bio *bio;
+ struct folio *zero_folio = largest_zero_folio();
+ int nr_vecs = max(1, i_blocksize(inode) / folio_size(zero_folio));

if (!len)
return 0;
+
/*
- * Max block size supported is 64k
+ * This limit shall never be reached as most filesystems have a
+ * maximum blocksize of 64k.
*/
- if (WARN_ON_ONCE(len > IOMAP_ZERO_PAGE_SIZE))
+ if (WARN_ON_ONCE(nr_vecs > BIO_MAX_VECS))
return -EINVAL;

- bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
+ bio = iomap_dio_alloc_bio(iter, dio, nr_vecs,
+ REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
GFP_KERNEL);
bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
bio->bi_private = dio;
bio->bi_end_io = iomap_dio_bio_end_io;

- __bio_add_page(bio, zero_page, len, 0);
+ while (len > 0) {
+ unsigned int io_len = min(len, folio_size(zero_folio));
+
+ bio_add_folio_nofail(bio, zero_folio, io_len, 0);
+ len -= io_len;
+ }
iomap_dio_submit_bio(iter, dio, bio, pos);
+
return 0;
}

@@ -822,15 +826,3 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
return iomap_dio_complete(dio);
}
EXPORT_SYMBOL_GPL(iomap_dio_rw);
-
-static int __init iomap_dio_init(void)
-{
- zero_page = alloc_pages(GFP_KERNEL | __GFP_ZERO,
- IOMAP_ZERO_PAGE_ORDER);
-
- if (!zero_page)
- return -ENOMEM;
-
- return 0;
-}
-fs_initcall(iomap_dio_init);

base-commit: 931e46dcbc7e6035a90e9c4a27a84b660e083f0a
--
2.50.1