On Wed, May 23, 2018 at 04:43:24PM +0200, Christoph Hellwig wrote:
> For the upcoming removal of buffer heads in XFS we need to keep track of
> the number of outstanding writeback requests per page. For this we need
> to know if bio_add_page merged a region with the previous bvec or not.
> Instead of adding additional arguments this refactors bio_add_page to
> be implemented using three lower level helpers which users like XFS can
> use directly if they care about the merge decisions.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> Reviewed-by: Jens Axboe <axboe@xxxxxxxxx>
Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> block/bio.c | 96 +++++++++++++++++++++++++++++----------------
> include/linux/bio.h | 9 +++++
> 2 files changed, 72 insertions(+), 33 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 53e0f0a1ed94..fdf635d42bbd 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -773,7 +773,7 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
> return 0;
> }
>
> - if (bio->bi_vcnt >= bio->bi_max_vecs)
> + if (bio_full(bio))
> return 0;
>
> /*
> @@ -821,52 +821,82 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
> EXPORT_SYMBOL(bio_add_pc_page);
>
> /**
> - * bio_add_page - attempt to add page to bio
> - * @bio: destination bio
> - * @page: page to add
> - * @len: vec entry length
> - * @offset: vec entry offset
> + * __bio_try_merge_page - try appending data to an existing bvec.
> + * @bio: destination bio
> + * @page: page to add
> + * @len: length of the data to add
> + * @off: offset of the data in @page
> *
> - * Attempt to add a page to the bio_vec maplist. This will only fail
> - * if either bio->bi_vcnt == bio->bi_max_vecs or it's a cloned bio.
> + * Try to add the data at @page + @off to the last bvec of @bio. This is a
> + * a useful optimisation for file systems with a block size smaller than the
> + * page size.
> + *
> + * Return %true on success or %false on failure.
> */
> -int bio_add_page(struct bio *bio, struct page *page,
> - unsigned int len, unsigned int offset)
> +bool __bio_try_merge_page(struct bio *bio, struct page *page,
> + unsigned int len, unsigned int off)
> {
> - struct bio_vec *bv;
> -
> - /*
> - * cloned bio must not modify vec list
> - */
> if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
> - return 0;
> + return false;
>
> - /*
> - * For filesystems with a blocksize smaller than the pagesize
> - * we will often be called with the same page as last time and
> - * a consecutive offset. Optimize this special case.
> - */
> if (bio->bi_vcnt > 0) {
> - bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
> + struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
>
> - if (page == bv->bv_page &&
> - offset == bv->bv_offset + bv->bv_len) {
> + if (page == bv->bv_page && off == bv->bv_offset + bv->bv_len) {
> bv->bv_len += len;
> - goto done;
> + bio->bi_iter.bi_size += len;
> + return true;
> }
> }
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(__bio_try_merge_page);
>
> - if (bio->bi_vcnt >= bio->bi_max_vecs)
> - return 0;
> +/**
> + * __bio_add_page - add page to a bio in a new segment
> + * @bio: destination bio
> + * @page: page to add
> + * @len: length of the data to add
> + * @off: offset of the data in @page
> + *
> + * Add the data at @page + @off to @bio as a new bvec. The caller must ensure
> + * that @bio has space for another bvec.
> + */
> +void __bio_add_page(struct bio *bio, struct page *page,
> + unsigned int len, unsigned int off)
> +{
> + struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt];
>
> - bv = &bio->bi_io_vec[bio->bi_vcnt];
> - bv->bv_page = page;
> - bv->bv_len = len;
> - bv->bv_offset = offset;
> + WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
> + WARN_ON_ONCE(bio_full(bio));
> +
> + bv->bv_page = page;
> + bv->bv_offset = off;
> + bv->bv_len = len;
>
> - bio->bi_vcnt++;
> -done:
> bio->bi_iter.bi_size += len;
> + bio->bi_vcnt++;
> +}
> +EXPORT_SYMBOL_GPL(__bio_add_page);
> +
> +/**
> + * bio_add_page - attempt to add page to bio
> + * @bio: destination bio
> + * @page: page to add
> + * @len: vec entry length
> + * @offset: vec entry offset
> + *
> + * Attempt to add a page to the bio_vec maplist. This will only fail
> + * if either bio->bi_vcnt == bio->bi_max_vecs or it's a cloned bio.
> + */
> +int bio_add_page(struct bio *bio, struct page *page,
> + unsigned int len, unsigned int offset)
> +{
> + if (!__bio_try_merge_page(bio, page, len, offset)) {
> + if (bio_full(bio))
> + return 0;
> + __bio_add_page(bio, page, len, offset);
> + }
> return len;
> }
> EXPORT_SYMBOL(bio_add_page);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index ce547a25e8ae..3e73c8bc25ea 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -123,6 +123,11 @@ static inline void *bio_data(struct bio *bio)
> return NULL;
> }
>
> +static inline bool bio_full(struct bio *bio)
> +{
> + return bio->bi_vcnt >= bio->bi_max_vecs;
> +}
> +
> /*
> * will die
> */
> @@ -470,6 +475,10 @@ void bio_chain(struct bio *, struct bio *);
> extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
> extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
> unsigned int, unsigned int);
> +bool __bio_try_merge_page(struct bio *bio, struct page *page,
> + unsigned int len, unsigned int off);
> +void __bio_add_page(struct bio *bio, struct page *page,
> + unsigned int len, unsigned int off);
> int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);
> struct rq_map_data;
> extern struct bio *bio_map_user_iov(struct request_queue *,
> --
> 2.17.0
>
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