Re: [PATCH v3 6/7] bio: add a helper calculating nr segments to alloc

Ming Lei
2021-01-11T02:59:30Z

On Sat, Jan 09, 2021 at 04:03:02PM +0000, Pavel Begunkov wrote:
> Add a helper function calculating the number of bvec segments we need to
> allocate to construct a bio. It doesn't change anything functionally,
> but will be used to not duplicate special cases in the future.
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> fs/block_dev.c | 7 ++++---
> fs/iomap/direct-io.c | 9 ++++-----
> include/linux/bio.h | 10 ++++++++++
> 3 files changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 3b8963e228a1..6f5bd9950baf 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -416,7 +416,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
> dio->size += bio->bi_iter.bi_size;
> pos += bio->bi_iter.bi_size;
>
> - nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
> + nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_PAGES);
> if (!nr_pages) {
> bool polled = false;
>
> @@ -481,9 +481,10 @@ blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> {
> int nr_pages;
>
> - nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES + 1);
> - if (!nr_pages)
> + if (!iov_iter_count(iter))
> return 0;
> +
> + nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_PAGES + 1);
> if (is_sync_kiocb(iocb) && nr_pages <= BIO_MAX_PAGES)
> return __blkdev_direct_IO_simple(iocb, iter, nr_pages);
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 933f234d5bec..ea1e8f696076 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -250,11 +250,8 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> orig_count = iov_iter_count(dio->submit.iter);
> iov_iter_truncate(dio->submit.iter, length);
>
> - nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
> - if (nr_pages <= 0) {
> - ret = nr_pages;
> + if (!iov_iter_count(dio->submit.iter))
> goto out;
> - }
>
> if (need_zeroout) {
> /* zero out from the start of the block to the write offset */
> @@ -263,6 +260,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> iomap_dio_zero(dio, iomap, pos - pad, pad);
> }
>
> + nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_PAGES);
> do {
> size_t n;
> if (dio->error) {
> @@ -308,7 +306,8 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> dio->size += n;
> copied += n;
>
> - nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
> + nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
> + BIO_MAX_PAGES);
> iomap_dio_submit_bio(dio, iomap, bio, pos);
> pos += n;
> } while (nr_pages);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 1edda614f7ce..d8f9077c43ef 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -10,6 +10,7 @@
> #include <linux/ioprio.h>
> /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
> #include <linux/blk_types.h>
> +#include <linux/uio.h>
>
> #define BIO_DEBUG
>
> @@ -441,6 +442,15 @@ static inline void bio_wouldblock_error(struct bio *bio)
> bio_endio(bio);
> }
>
> +/*
> + * Calculate number of bvec segments that should be allocated to fit data
> + * pointed by @iter.
> + */
> +static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
> +{
> + return iov_iter_npages(iter, max_segs);
> +}
> +
> struct request_queue;
>
> extern int submit_bio_wait(struct bio *bio);
> --
> 2.24.0
>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

--
Ming