On Wed, May 9, 2018 at 3:47 PM, Christoph Hellwig <hch@xxxxxx> 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.
The merge policy may be transparent to fs, such as multipage bvec.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> block/bio.c | 87 ++++++++++++++++++++++++++++++---------------
> include/linux/bio.h | 9 +++++
> 2 files changed, 67 insertions(+), 29 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 53e0f0a1ed94..6ceba6adbf42 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;
>
> /*
> @@ -820,6 +820,59 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
> }
> EXPORT_SYMBOL(bio_add_pc_page);
>
> +/**
> + * __bio_try_merge_page - try adding data to an existing bvec
> + * @bio: destination bio
> + * @page: page to add
> + * @len: length of the range to add
> + * @off: offset into @page
> + *
> + * Try adding the data described at @page + @offset to the last bvec of @bio.
> + * Return %true on success or %false on failure. This can happen frequently
> + * for file systems with a block size smaller than the page size.
> + */
> +bool __bio_try_merge_page(struct bio *bio, struct page *page,
> + unsigned int len, unsigned int off)
> +{
> + if (bio->bi_vcnt > 0) {
> + struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
> +
> + if (page == bv->bv_page && off == bv->bv_offset + bv->bv_len) {
> + bv->bv_len += len;
> + bio->bi_iter.bi_size += len;
> + return true;
> + }
> + }
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(__bio_try_merge_page);
> +
> +/**
> + * __bio_add_page - add page to a bio in a new segment
> + * @bio: destination bio
> + * @page: page to add
> + * @len: length of the range to add
> + * @off: offset into @page
> + *
> + * Add the data at @page + @offset 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];
> +
> + WARN_ON_ONCE(bio_full(bio));
> +
> + bv->bv_page = page;
> + bv->bv_offset = off;
> + bv->bv_len = len;
> +
> + bio->bi_iter.bi_size += len;
> + bio->bi_vcnt++;
> +}
> +EXPORT_SYMBOL_GPL(__bio_add_page);
Given both __bio_try_merge_page() and __bio_add_page() are exported,
please add WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)), otherwise
both may be misused by external users.
--
Ming Lei
