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

Darrick J. Wong
2025-08-14T18:27:14Z

On Thu, Aug 14, 2025 at 04:21:37PM +0200, Pankaj Raghav (Samsung) wrote:
> 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>

Seems fine to me, though I wonder if this oughn't go along with the
rest of the largest_zero_folio changes?

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
> 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
>
>