On Mon, Jun 10, 2019 at 06:34:46AM -0700, Christoph Hellwig wrote:
> I don't really like the magic enum types. I'd rather go back to my
> initial idea to turn the same_page argument into an output parameter,
> so that the callers can act upon it. Untested patch below:
>
>
> diff --git a/block/bio.c b/block/bio.c
> index 683cbb40f051..d4999ef3b1fb 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -636,7 +636,7 @@ EXPORT_SYMBOL(bio_clone_fast);
>
> static inline bool page_is_mergeable(const struct bio_vec *bv,
> struct page *page, unsigned int len, unsigned int off,
> - bool same_page)
> + bool *same_page)
> {
> phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) +
> bv->bv_offset + bv->bv_len - 1;
> @@ -647,26 +647,17 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
> if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
> return false;
>
> - if ((vec_end_addr & PAGE_MASK) != page_addr) {
> - if (same_page)
> - return false;
> - if (pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
> - return false;
> - }
> -
> - WARN_ON_ONCE(same_page && (len + off) > PAGE_SIZE);
> -
> + *same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
> + if (!*same_page && pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
> + return false;
> return true;
> }
>
> -/*
> - * Check if the @page can be added to the current segment(@bv), and make
> - * sure to call it only if page_is_mergeable(@bv, @page) is true
> - */
> -static bool can_add_page_to_seg(struct request_queue *q,
> - struct bio_vec *bv, struct page *page, unsigned len,
> - unsigned offset)
> +static bool bio_try_merge_pc_page(struct request_queue *q, struct bio *bio,
> + struct page *page, unsigned len, unsigned offset,
> + bool *same_page)
> {
> + struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
> unsigned long mask = queue_segment_boundary(q);
> phys_addr_t addr1 = page_to_phys(bv->bv_page) + bv->bv_offset;
> phys_addr_t addr2 = page_to_phys(page) + offset + len - 1;
> @@ -677,7 +668,13 @@ static bool can_add_page_to_seg(struct request_queue *q,
> if (bv->bv_len + len > queue_max_segment_size(q))
> return false;
>
> - return true;
> + /*
> + * If the queue doesn't support SG gaps and adding this
> + * offset would create a gap, disallow it.
> + */
> + if (bvec_gap_to_prev(q, bv, offset))
> + return false;
> + return __bio_try_merge_page(bio, page, len, offset, same_page);
> }
>
> /**
> @@ -701,6 +698,7 @@ static int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
> bool put_same_page)
> {
> struct bio_vec *bvec;
> + bool same_page = false;
>
> /*
> * cloned bio must not modify vec list
> @@ -711,29 +709,11 @@ static int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
> if (((bio->bi_iter.bi_size + len) >> 9) > queue_max_hw_sectors(q))
> return 0;
>
> - if (bio->bi_vcnt > 0) {
> - bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
> -
> - if (page == bvec->bv_page &&
> - offset == bvec->bv_offset + bvec->bv_len) {
> - if (put_same_page)
> - put_page(page);
> - bvec->bv_len += len;
> - goto done;
> - }
> -
> - /*
> - * If the queue doesn't support SG gaps and adding this
> - * offset would create a gap, disallow it.
> - */
> - if (bvec_gap_to_prev(q, bvec, offset))
> - return 0;
> -
> - if (page_is_mergeable(bvec, page, len, offset, false) &&
> - can_add_page_to_seg(q, bvec, page, len, offset)) {
> - bvec->bv_len += len;
> - goto done;
> - }
> + if (bio->bi_vcnt > 0 &&
> + bio_try_merge_pc_page(q, bio, page, len, offset, &same_page)) {
> + if (put_same_page && same_page)
> + put_page(page);
> + goto done;
> }
>
> if (bio_full(bio))
> @@ -747,8 +727,8 @@ static int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
> bvec->bv_len = len;
> bvec->bv_offset = offset;
> bio->bi_vcnt++;
> - done:
> bio->bi_iter.bi_size += len;
> + done:
> bio->bi_phys_segments = bio->bi_vcnt;
> bio_set_flag(bio, BIO_SEG_VALID);
> return len;
> @@ -767,8 +747,7 @@ EXPORT_SYMBOL(bio_add_pc_page);
> * @page: start page to add
> * @len: length of the data to add
> * @off: offset of the data relative to @page
> - * @same_page: if %true only merge if the new data is in the same physical
> - * page as the last segment of the bio.
> + * @same_page: return if the segment has been merged inside the same page
> *
> * 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
> @@ -779,7 +758,7 @@ EXPORT_SYMBOL(bio_add_pc_page);
> * Return %true on success or %false on failure.
> */
> bool __bio_try_merge_page(struct bio *bio, struct page *page,
> - unsigned int len, unsigned int off, bool same_page)
> + unsigned int len, unsigned int off, bool *same_page)
> {
> if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
> return false;
> @@ -837,7 +816,9 @@ EXPORT_SYMBOL_GPL(__bio_add_page);
> 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, false)) {
> + bool same_page = false;
> +
> + if (!__bio_try_merge_page(bio, page, len, offset, &same_page)) {
> if (bio_full(bio))
> return 0;
> __bio_add_page(bio, page, len, offset);
> @@ -900,6 +881,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
> struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
> struct page **pages = (struct page **)bv;
> + bool same_page = false;
> ssize_t size, left;
> unsigned len, i;
> size_t offset;
> @@ -920,8 +902,15 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> struct page *page = pages[i];
>
> len = min_t(size_t, PAGE_SIZE - offset, left);
> - if (WARN_ON_ONCE(bio_add_page(bio, page, len, offset) != len))
> - return -EINVAL;
> +
> + if (__bio_try_merge_page(bio, page, len, offset, &same_page)) {
> + if (same_page)
> + put_page(page);
> + } else {
> + if (WARN_ON_ONCE(bio_full(bio)))
> + return -EINVAL;
> + __bio_add_page(bio, page, len, offset);
> + }
> offset = 0;
> }
>
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 23ef63fd1669..12654c2e78f8 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -287,7 +287,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> struct iomap_readpage_ctx *ctx = data;
> struct page *page = ctx->cur_page;
> struct iomap_page *iop = iomap_page_create(inode, page);
> - bool is_contig = false;
> + bool same_page = false, is_contig = false;
> loff_t orig_pos = pos;
> unsigned poff, plen;
> sector_t sector;
> @@ -315,10 +315,14 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> * Try to merge into a previous segment if we can.
> */
> sector = iomap_sector(iomap, pos);
> - if (ctx->bio && bio_end_sector(ctx->bio) == sector) {
> - if (__bio_try_merge_page(ctx->bio, page, plen, poff, true))
> - goto done;
> + if (ctx->bio && bio_end_sector(ctx->bio) == sector)
> is_contig = true;
> +
> + if (is_contig &&
> + __bio_try_merge_page(ctx->bio, page, plen, poff, &same_page)) {
> + if (!same_page && iop)
> + atomic_inc(&iop->read_count);
> + goto done;
> }
>
> /*
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index a6f0f4761a37..8da5e6637771 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -758,6 +758,7 @@ xfs_add_to_ioend(
> struct block_device *bdev = xfs_find_bdev_for_inode(inode);
> unsigned len = i_blocksize(inode);
> unsigned poff = offset & (PAGE_SIZE - 1);
> + bool merged, same_page = false;
> sector_t sector;
>
> sector = xfs_fsb_to_db(ip, wpc->imap.br_startblock) +
> @@ -774,9 +775,13 @@ xfs_add_to_ioend(
> wpc->imap.br_state, offset, bdev, sector);
> }
>
> - if (!__bio_try_merge_page(wpc->ioend->io_bio, page, len, poff, true)) {
> - if (iop)
> - atomic_inc(&iop->write_count);
> + merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
> + &same_page);
> +
> + if (iop && !same_page)
> + atomic_inc(&iop->write_count);
> +
> + if (!merged) {
> if (bio_full(wpc->ioend->io_bio))
> xfs_chain_bio(wpc->ioend, wbc, bdev, sector);
> bio_add_page(wpc->ioend->io_bio, page, len, poff);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index ea73df36529a..3df3b127b394 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -423,7 +423,7 @@ 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, bool same_page);
> + unsigned int len, unsigned int off, bool *same_page);
> 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);
I'd suggest to take a look at V3, in which each flag is documented well
enough, and it is much more simpler than this one.
Also maybe other callers need to pass BVEC_MERGE_PUT_SAME_PAGE.
Thanks,
Ming
