simplify passthrough bio handling

simplify passthrough bio handling

[Christoph Hellwig]

Hi Jens,

this series removes the special casing when adding pages to passthrough
bios in favor of simply checking that they match the queue limits once
before submissions.  This mirrors where the zone append users have been
moving and a recent doing the same for a single optimizes passthrough
user.

Diffstat:
 block/bio.c                        |  107 +-----------------------------
 block/blk-map.c                    |  128 ++++++++++---------------------------
 block/blk-mq.c                     |    4 -
 block/blk.h                        |    8 --
 drivers/nvme/target/passthru.c     |   18 +++--
 drivers/nvme/target/zns.c          |    3 
 drivers/target/target_core_pscsi.c |    6 -
 include/linux/bio.h                |    2 
 include/linux/blk-mq.h             |    8 --
 9 files changed, 57 insertions(+), 227 deletions(-)

[PATCH 1/2] block: remove bio_add_pc_page

[Christoph Hellwig]

Lift bio_split_rw_at into blk_rq_append_bio so that it validates the
hardware limits.  With this all passthrough callers can simply add
bio_add_page to build the bio and delay checking for exceeding of limits
to this point instead of doing it for each page.

While this looks like adding a new expensive loop over all bio_vecs,
blk_rq_append_bio is already doing that just to counter the number of
segments.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/bio.c                        | 107 ++------------------------
 block/blk-map.c                    | 118 +++++++----------------------
 block/blk.h                        |   8 --
 drivers/nvme/target/passthru.c     |  18 +++--
 drivers/nvme/target/zns.c          |   3 +-
 drivers/target/target_core_pscsi.c |   6 +-
 include/linux/bio.h                |   2 -
 7 files changed, 48 insertions(+), 214 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index d5bdc31d88d3..4e1a27d312c9 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -946,8 +946,11 @@ static bool bvec_try_merge_page(struct bio_vec *bv, struct page *page,
 
 /*
  * Try to merge a page into a segment, while obeying the hardware segment
- * size limit.  This is not for normal read/write bios, but for passthrough
- * or Zone Append operations that we can't split.
+ * size limit.
+ *
+ * This is kept around for the integrity metadata, which is still tries
+ * to build the initial bio to the hardware limit and doesn't have proper
+ * helpers to split.  Hopefully this will go away soon.
  */
 bool bvec_try_merge_hw_page(struct request_queue *q, struct bio_vec *bv,
 		struct page *page, unsigned len, unsigned offset,
@@ -964,106 +967,6 @@ bool bvec_try_merge_hw_page(struct request_queue *q, struct bio_vec *bv,
 	return bvec_try_merge_page(bv, page, len, offset, same_page);
 }
 
-/**
- * bio_add_hw_page - attempt to add a page to a bio with hw constraints
- * @q: the target queue
- * @bio: destination bio
- * @page: page to add
- * @len: vec entry length
- * @offset: vec entry offset
- * @max_sectors: maximum number of sectors that can be added
- * @same_page: return if the segment has been merged inside the same page
- *
- * Add a page to a bio while respecting the hardware max_sectors, max_segment
- * and gap limitations.
- */
-int bio_add_hw_page(struct request_queue *q, struct bio *bio,
-		struct page *page, unsigned int len, unsigned int offset,
-		unsigned int max_sectors, bool *same_page)
-{
-	unsigned int max_size = max_sectors << SECTOR_SHIFT;
-
-	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
-		return 0;
-
-	len = min3(len, max_size, queue_max_segment_size(q));
-	if (len > max_size - bio->bi_iter.bi_size)
-		return 0;
-
-	if (bio->bi_vcnt > 0) {
-		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
-
-		if (bvec_try_merge_hw_page(q, bv, page, len, offset,
-				same_page)) {
-			bio->bi_iter.bi_size += len;
-			return len;
-		}
-
-		if (bio->bi_vcnt >=
-		    min(bio->bi_max_vecs, queue_max_segments(q)))
-			return 0;
-
-		/*
-		 * If the queue doesn't support SG gaps and adding this segment
-		 * would create a gap, disallow it.
-		 */
-		if (bvec_gap_to_prev(&q->limits, bv, offset))
-			return 0;
-	}
-
-	bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], page, len, offset);
-	bio->bi_vcnt++;
-	bio->bi_iter.bi_size += len;
-	return len;
-}
-
-/**
- * bio_add_hw_folio - attempt to add a folio to a bio with hw constraints
- * @q: the target queue
- * @bio: destination bio
- * @folio: folio to add
- * @len: vec entry length
- * @offset: vec entry offset in the folio
- * @max_sectors: maximum number of sectors that can be added
- * @same_page: return if the segment has been merged inside the same folio
- *
- * Add a folio to a bio while respecting the hardware max_sectors, max_segment
- * and gap limitations.
- */
-int bio_add_hw_folio(struct request_queue *q, struct bio *bio,
-		struct folio *folio, size_t len, size_t offset,
-		unsigned int max_sectors, bool *same_page)
-{
-	if (len > UINT_MAX || offset > UINT_MAX)
-		return 0;
-	return bio_add_hw_page(q, bio, folio_page(folio, 0), len, offset,
-			       max_sectors, same_page);
-}
-
-/**
- * bio_add_pc_page	- attempt to add page to passthrough bio
- * @q: the target queue
- * @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 can fail for a
- * number of reasons, such as the bio being full or target block device
- * limitations. The target block device must allow bio's up to PAGE_SIZE,
- * so it is always possible to add a single page to an empty bio.
- *
- * This should only be used by passthrough bios.
- */
-int bio_add_pc_page(struct request_queue *q, struct bio *bio,
-		struct page *page, unsigned int len, unsigned int offset)
-{
-	bool same_page = false;
-	return bio_add_hw_page(q, bio, page, len, offset,
-			queue_max_hw_sectors(q), &same_page);
-}
-EXPORT_SYMBOL(bio_add_pc_page);
-
 /**
  * __bio_add_page - add page(s) to a bio in a new segment
  * @bio: destination bio
diff --git a/block/blk-map.c b/block/blk-map.c
index 894009b2d881..67a2da3b7ed9 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -189,7 +189,7 @@ static int bio_copy_user_iov(struct request *rq, struct rq_map_data *map_data,
 			}
 		}
 
-		if (bio_add_pc_page(rq->q, bio, page, bytes, offset) < bytes) {
+		if (bio_add_page(bio, page, bytes, offset) < bytes) {
 			if (!map_data)
 				__free_page(page);
 			break;
@@ -272,86 +272,27 @@ static struct bio *blk_rq_map_bio_alloc(struct request *rq,
 static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 		gfp_t gfp_mask)
 {
-	iov_iter_extraction_t extraction_flags = 0;
-	unsigned int max_sectors = queue_max_hw_sectors(rq->q);
 	unsigned int nr_vecs = iov_iter_npages(iter, BIO_MAX_VECS);
 	struct bio *bio;
 	int ret;
-	int j;
 
 	if (!iov_iter_count(iter))
 		return -EINVAL;
 
 	bio = blk_rq_map_bio_alloc(rq, nr_vecs, gfp_mask);
-	if (bio == NULL)
+	if (!bio)
 		return -ENOMEM;
-
-	if (blk_queue_pci_p2pdma(rq->q))
-		extraction_flags |= ITER_ALLOW_P2PDMA;
-	if (iov_iter_extract_will_pin(iter))
-		bio_set_flag(bio, BIO_PAGE_PINNED);
-
-	while (iov_iter_count(iter)) {
-		struct page *stack_pages[UIO_FASTIOV];
-		struct page **pages = stack_pages;
-		ssize_t bytes;
-		size_t offs;
-		int npages;
-
-		if (nr_vecs > ARRAY_SIZE(stack_pages))
-			pages = NULL;
-
-		bytes = iov_iter_extract_pages(iter, &pages, LONG_MAX,
-					       nr_vecs, extraction_flags, &offs);
-		if (unlikely(bytes <= 0)) {
-			ret = bytes ? bytes : -EFAULT;
-			goto out_unmap;
-		}
-
-		npages = DIV_ROUND_UP(offs + bytes, PAGE_SIZE);
-
-		if (unlikely(offs & queue_dma_alignment(rq->q)))
-			j = 0;
-		else {
-			for (j = 0; j < npages; j++) {
-				struct page *page = pages[j];
-				unsigned int n = PAGE_SIZE - offs;
-				bool same_page = false;
-
-				if (n > bytes)
-					n = bytes;
-
-				if (!bio_add_hw_page(rq->q, bio, page, n, offs,
-						     max_sectors, &same_page))
-					break;
-
-				if (same_page)
-					bio_release_page(bio, page);
-				bytes -= n;
-				offs = 0;
-			}
-		}
-		/*
-		 * release the pages we didn't map into the bio, if any
-		 */
-		while (j < npages)
-			bio_release_page(bio, pages[j++]);
-		if (pages != stack_pages)
-			kvfree(pages);
-		/* couldn't stuff something into bio? */
-		if (bytes) {
-			iov_iter_revert(iter, bytes);
-			break;
-		}
-	}
-
+	ret = bio_iov_iter_get_pages(bio, iter);
+	if (ret)
+		goto out_put;
 	ret = blk_rq_append_bio(rq, bio);
 	if (ret)
-		goto out_unmap;
+		goto out_release;
 	return 0;
 
- out_unmap:
+out_release:
 	bio_release_pages(bio, false);
+out_put:
 	blk_mq_map_bio_put(bio);
 	return ret;
 }
@@ -422,8 +363,7 @@ static struct bio *bio_map_kern(struct request_queue *q, void *data,
 			page = virt_to_page(data);
 		else
 			page = vmalloc_to_page(data);
-		if (bio_add_pc_page(q, bio, page, bytes,
-				    offset) < bytes) {
+		if (bio_add_page(bio, page, bytes, offset) < bytes) {
 			/* we don't support partial mappings */
 			bio_uninit(bio);
 			kfree(bio);
@@ -507,7 +447,7 @@ static struct bio *bio_copy_kern(struct request_queue *q, void *data,
 		if (!reading)
 			memcpy(page_address(page), p, bytes);
 
-		if (bio_add_pc_page(q, bio, page, bytes, 0) < bytes)
+		if (bio_add_page(bio, page, bytes, 0) < bytes)
 			break;
 
 		len -= bytes;
@@ -536,12 +476,19 @@ static struct bio *bio_copy_kern(struct request_queue *q, void *data,
  */
 int blk_rq_append_bio(struct request *rq, struct bio *bio)
 {
-	struct bvec_iter iter;
-	struct bio_vec bv;
+	const struct queue_limits *lim = &rq->q->limits;
+	unsigned int max_bytes = lim->max_hw_sectors << SECTOR_SHIFT;
 	unsigned int nr_segs = 0;
+	int ret;
 
-	bio_for_each_bvec(bv, bio, iter)
-		nr_segs++;
+	/* check that the data layout matches the hardware restrictions */
+	ret = bio_split_rw_at(bio, lim, &nr_segs, max_bytes);
+	if (ret) {
+		/* if we would have to split the bio, copy instead */
+		if (ret > 0)
+			ret = -EREMOTEIO;
+		return ret;
+	}
 
 	if (!rq->bio) {
 		blk_rq_bio_prep(rq, bio, nr_segs);
@@ -561,9 +508,7 @@ EXPORT_SYMBOL(blk_rq_append_bio);
 /* Prepare bio for passthrough IO given ITER_BVEC iter */
 static int blk_rq_map_user_bvec(struct request *rq, const struct iov_iter *iter)
 {
-	const struct queue_limits *lim = &rq->q->limits;
-	unsigned int max_bytes = lim->max_hw_sectors << SECTOR_SHIFT;
-	unsigned int nsegs;
+	unsigned int max_bytes = rq->q->limits.max_hw_sectors << SECTOR_SHIFT;
 	struct bio *bio;
 	int ret;
 
@@ -576,18 +521,10 @@ static int blk_rq_map_user_bvec(struct request *rq, const struct iov_iter *iter)
 		return -ENOMEM;
 	bio_iov_bvec_set(bio, iter);
 
-	/* check that the data layout matches the hardware restrictions */
-	ret = bio_split_rw_at(bio, lim, &nsegs, max_bytes);
-	if (ret) {
-		/* if we would have to split the bio, copy instead */
-		if (ret > 0)
-			ret = -EREMOTEIO;
+	ret = blk_rq_append_bio(rq, bio);
+	if (ret)
 		blk_mq_map_bio_put(bio);
-		return ret;
-	}
-
-	blk_rq_bio_prep(rq, bio, nsegs);
-	return 0;
+	return ret;
 }
 
 /**
@@ -644,8 +581,11 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 			ret = bio_copy_user_iov(rq, map_data, &i, gfp_mask);
 		else
 			ret = bio_map_user_iov(rq, &i, gfp_mask);
-		if (ret)
+		if (ret) {
+			if (ret == -EREMOTEIO)
+				ret = -EINVAL;
 			goto unmap_rq;
+		}
 		if (!bio)
 			bio = rq->bio;
 	} while (iov_iter_count(&i));
diff --git a/block/blk.h b/block/blk.h
index cbf6a676ffe9..4904b86d5fec 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -556,14 +556,6 @@ void bdev_set_nr_sectors(struct block_device *bdev, sector_t sectors);
 struct gendisk *__alloc_disk_node(struct request_queue *q, int node_id,
 		struct lock_class_key *lkclass);
 
-int bio_add_hw_page(struct request_queue *q, struct bio *bio,
-		struct page *page, unsigned int len, unsigned int offset,
-		unsigned int max_sectors, bool *same_page);
-
-int bio_add_hw_folio(struct request_queue *q, struct bio *bio,
-		struct folio *folio, size_t len, size_t offset,
-		unsigned int max_sectors, bool *same_page);
-
 /*
  * Clean up a page appropriately, where the page may be pinned, may have a
  * ref taken on it or neither.
diff --git a/drivers/nvme/target/passthru.c b/drivers/nvme/target/passthru.c
index 30b21936b0c6..26e2907ce8bb 100644
--- a/drivers/nvme/target/passthru.c
+++ b/drivers/nvme/target/passthru.c
@@ -261,6 +261,7 @@ static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
 {
 	struct scatterlist *sg;
 	struct bio *bio;
+	int ret = -EINVAL;
 	int i;
 
 	if (req->sg_cnt > BIO_MAX_VECS)
@@ -277,16 +278,19 @@ static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
 	}
 
 	for_each_sg(req->sg, sg, req->sg_cnt, i) {
-		if (bio_add_pc_page(rq->q, bio, sg_page(sg), sg->length,
-				    sg->offset) < sg->length) {
-			nvmet_req_bio_put(req, bio);
-			return -EINVAL;
-		}
+		if (bio_add_page(bio, sg_page(sg), sg->length, sg->offset) <
+				sg->length)
+			goto out_bio_put;
 	}
 
-	blk_rq_bio_prep(rq, bio, req->sg_cnt);
-
+	ret = blk_rq_append_bio(rq, bio);
+	if (ret)
+		goto out_bio_put;
 	return 0;
+
+out_bio_put:
+	nvmet_req_bio_put(req, bio);
+	return ret;
 }
 
 static void nvmet_passthru_execute_cmd(struct nvmet_req *req)
diff --git a/drivers/nvme/target/zns.c b/drivers/nvme/target/zns.c
index 3aef35b05111..29a60fabfcc8 100644
--- a/drivers/nvme/target/zns.c
+++ b/drivers/nvme/target/zns.c
@@ -586,8 +586,7 @@ void nvmet_bdev_execute_zone_append(struct nvmet_req *req)
 	for_each_sg(req->sg, sg, req->sg_cnt, sg_cnt) {
 		unsigned int len = sg->length;
 
-		if (bio_add_pc_page(bdev_get_queue(bio->bi_bdev), bio,
-				sg_page(sg), len, sg->offset) != len) {
+		if (bio_add_page(bio, sg_page(sg), len, sg->offset) != len) {
 			status = NVME_SC_INTERNAL;
 			goto out_put_bio;
 		}
diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 287ac5b0495f..f991cf759836 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c
@@ -823,7 +823,6 @@ static sense_reason_t
 pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 		struct request *req)
 {
-	struct pscsi_dev_virt *pdv = PSCSI_DEV(cmd->se_dev);
 	struct bio *bio = NULL;
 	struct page *page;
 	struct scatterlist *sg;
@@ -871,12 +870,11 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 					(rw) ? "rw" : "r", nr_vecs);
 			}
 
-			pr_debug("PSCSI: Calling bio_add_pc_page() i: %d"
+			pr_debug("PSCSI: Calling bio_add_page() i: %d"
 				" bio: %p page: %p len: %d off: %d\n", i, bio,
 				page, len, off);
 
-			rc = bio_add_pc_page(pdv->pdv_sd->request_queue,
-					bio, page, bytes, off);
+			rc = bio_add_page(bio, page, bytes, off);
 			pr_debug("PSCSI: bio->bi_vcnt: %d nr_vecs: %d\n",
 				bio_segments(bio), nr_vecs);
 			if (rc != bytes) {
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 1eec59699100..4b79bf50f4f0 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -413,8 +413,6 @@ int __must_check bio_add_page(struct bio *bio, struct page *page, unsigned len,
 			      unsigned off);
 bool __must_check bio_add_folio(struct bio *bio, struct folio *folio,
 				size_t len, size_t off);
-extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
-			   unsigned int, unsigned int);
 void __bio_add_page(struct bio *bio, struct page *page,
 		unsigned int len, unsigned int off);
 void bio_add_folio_nofail(struct bio *bio, struct folio *folio, size_t len,
-- 
2.45.2

[PATCH 2/2] block: remove blk_rq_bio_prep

[Christoph Hellwig]

There is not real point in a helper just to assign three values to four
fields, especially when the surrounding code is working on the
neighbor fields directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-map.c        | 10 ++++++----
 block/blk-mq.c         |  4 +++-
 include/linux/blk-mq.h |  8 --------
 3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/block/blk-map.c b/block/blk-map.c
index 67a2da3b7ed9..d2f22744b3d1 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -490,17 +490,19 @@ int blk_rq_append_bio(struct request *rq, struct bio *bio)
 		return ret;
 	}
 
-	if (!rq->bio) {
-		blk_rq_bio_prep(rq, bio, nr_segs);
-	} else {
+	if (rq->bio) {
 		if (!ll_back_merge_fn(rq, bio, nr_segs))
 			return -EINVAL;
 		rq->biotail->bi_next = bio;
 		rq->biotail = bio;
-		rq->__data_len += (bio)->bi_iter.bi_size;
+		rq->__data_len += bio->bi_iter.bi_size;
 		bio_crypt_free_ctx(bio);
+		return 0;
 	}
 
+	rq->nr_phys_segments = nr_segs;
+	rq->bio = rq->biotail = bio;
+	rq->__data_len = bio->bi_iter.bi_size;
 	return 0;
 }
 EXPORT_SYMBOL(blk_rq_append_bio);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 16feec6c11ab..2e6132f778fd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2658,8 +2658,10 @@ static void blk_mq_bio_to_request(struct request *rq, struct bio *bio,
 	if (bio->bi_opf & REQ_RAHEAD)
 		rq->cmd_flags |= REQ_FAILFAST_MASK;
 
+	rq->bio = rq->biotail = bio;
 	rq->__sector = bio->bi_iter.bi_sector;
-	blk_rq_bio_prep(rq, bio, nr_segs);
+	rq->__data_len = bio->bi_iter.bi_size;
+	rq->nr_phys_segments = nr_segs;
 	if (bio_integrity(bio))
 		rq->nr_integrity_segments = blk_rq_count_integrity_sg(rq->q,
 								      bio);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 2322b54a86ed..a0a9007cc1e3 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -968,14 +968,6 @@ static inline void blk_mq_cleanup_rq(struct request *rq)
 		rq->q->mq_ops->cleanup_rq(rq);
 }
 
-static inline void blk_rq_bio_prep(struct request *rq, struct bio *bio,
-		unsigned int nr_segs)
-{
-	rq->nr_phys_segments = nr_segs;
-	rq->__data_len = bio->bi_iter.bi_size;
-	rq->bio = rq->biotail = bio;
-}
-
 void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
 		struct lock_class_key *key);
 
-- 
2.45.2

Re: [PATCH 1/2] block: remove bio_add_pc_page

[Sagi Grimberg]

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>



On 03/01/2025 9:33, Christoph Hellwig wrote:
> Lift bio_split_rw_at into blk_rq_append_bio so that it validates the
> hardware limits.  With this all passthrough callers can simply add
> bio_add_page to build the bio and delay checking for exceeding of limits
> to this point instead of doing it for each page.
>
> While this looks like adding a new expensive loop over all bio_vecs,
> blk_rq_append_bio is already doing that just to counter the number of
> segments.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   block/bio.c                        | 107 ++------------------------
>   block/blk-map.c                    | 118 +++++++----------------------
>   block/blk.h                        |   8 --
>   drivers/nvme/target/passthru.c     |  18 +++--
>   drivers/nvme/target/zns.c          |   3 +-
>   drivers/target/target_core_pscsi.c |   6 +-
>   include/linux/bio.h                |   2 -
>   7 files changed, 48 insertions(+), 214 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index d5bdc31d88d3..4e1a27d312c9 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -946,8 +946,11 @@ static bool bvec_try_merge_page(struct bio_vec *bv, struct page *page,
>   
>   /*
>    * Try to merge a page into a segment, while obeying the hardware segment
> - * size limit.  This is not for normal read/write bios, but for passthrough
> - * or Zone Append operations that we can't split.
> + * size limit.
> + *
> + * This is kept around for the integrity metadata, which is still tries
> + * to build the initial bio to the hardware limit and doesn't have proper
> + * helpers to split.  Hopefully this will go away soon.
>    */
>   bool bvec_try_merge_hw_page(struct request_queue *q, struct bio_vec *bv,
>   		struct page *page, unsigned len, unsigned offset,
> @@ -964,106 +967,6 @@ bool bvec_try_merge_hw_page(struct request_queue *q, struct bio_vec *bv,
>   	return bvec_try_merge_page(bv, page, len, offset, same_page);
>   }
>   
> -/**
> - * bio_add_hw_page - attempt to add a page to a bio with hw constraints
> - * @q: the target queue
> - * @bio: destination bio
> - * @page: page to add
> - * @len: vec entry length
> - * @offset: vec entry offset
> - * @max_sectors: maximum number of sectors that can be added
> - * @same_page: return if the segment has been merged inside the same page
> - *
> - * Add a page to a bio while respecting the hardware max_sectors, max_segment
> - * and gap limitations.
> - */
> -int bio_add_hw_page(struct request_queue *q, struct bio *bio,
> -		struct page *page, unsigned int len, unsigned int offset,
> -		unsigned int max_sectors, bool *same_page)
> -{
> -	unsigned int max_size = max_sectors << SECTOR_SHIFT;
> -
> -	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
> -		return 0;
> -
> -	len = min3(len, max_size, queue_max_segment_size(q));
> -	if (len > max_size - bio->bi_iter.bi_size)
> -		return 0;
> -
> -	if (bio->bi_vcnt > 0) {
> -		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
> -
> -		if (bvec_try_merge_hw_page(q, bv, page, len, offset,
> -				same_page)) {
> -			bio->bi_iter.bi_size += len;
> -			return len;
> -		}
> -
> -		if (bio->bi_vcnt >=
> -		    min(bio->bi_max_vecs, queue_max_segments(q)))
> -			return 0;
> -
> -		/*
> -		 * If the queue doesn't support SG gaps and adding this segment
> -		 * would create a gap, disallow it.
> -		 */
> -		if (bvec_gap_to_prev(&q->limits, bv, offset))
> -			return 0;
> -	}
> -
> -	bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], page, len, offset);
> -	bio->bi_vcnt++;
> -	bio->bi_iter.bi_size += len;
> -	return len;
> -}
> -
> -/**
> - * bio_add_hw_folio - attempt to add a folio to a bio with hw constraints
> - * @q: the target queue
> - * @bio: destination bio
> - * @folio: folio to add
> - * @len: vec entry length
> - * @offset: vec entry offset in the folio
> - * @max_sectors: maximum number of sectors that can be added
> - * @same_page: return if the segment has been merged inside the same folio
> - *
> - * Add a folio to a bio while respecting the hardware max_sectors, max_segment
> - * and gap limitations.
> - */
> -int bio_add_hw_folio(struct request_queue *q, struct bio *bio,
> -		struct folio *folio, size_t len, size_t offset,
> -		unsigned int max_sectors, bool *same_page)
> -{
> -	if (len > UINT_MAX || offset > UINT_MAX)
> -		return 0;
> -	return bio_add_hw_page(q, bio, folio_page(folio, 0), len, offset,
> -			       max_sectors, same_page);
> -}
> -
> -/**
> - * bio_add_pc_page	- attempt to add page to passthrough bio
> - * @q: the target queue
> - * @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 can fail for a
> - * number of reasons, such as the bio being full or target block device
> - * limitations. The target block device must allow bio's up to PAGE_SIZE,
> - * so it is always possible to add a single page to an empty bio.
> - *
> - * This should only be used by passthrough bios.
> - */
> -int bio_add_pc_page(struct request_queue *q, struct bio *bio,
> -		struct page *page, unsigned int len, unsigned int offset)
> -{
> -	bool same_page = false;
> -	return bio_add_hw_page(q, bio, page, len, offset,
> -			queue_max_hw_sectors(q), &same_page);
> -}
> -EXPORT_SYMBOL(bio_add_pc_page);
> -
>   /**
>    * __bio_add_page - add page(s) to a bio in a new segment
>    * @bio: destination bio
> diff --git a/block/blk-map.c b/block/blk-map.c
> index 894009b2d881..67a2da3b7ed9 100644
> --- a/block/blk-map.c
> +++ b/block/blk-map.c
> @@ -189,7 +189,7 @@ static int bio_copy_user_iov(struct request *rq, struct rq_map_data *map_data,
>   			}
>   		}
>   
> -		if (bio_add_pc_page(rq->q, bio, page, bytes, offset) < bytes) {
> +		if (bio_add_page(bio, page, bytes, offset) < bytes) {
>   			if (!map_data)
>   				__free_page(page);
>   			break;
> @@ -272,86 +272,27 @@ static struct bio *blk_rq_map_bio_alloc(struct request *rq,
>   static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
>   		gfp_t gfp_mask)
>   {
> -	iov_iter_extraction_t extraction_flags = 0;
> -	unsigned int max_sectors = queue_max_hw_sectors(rq->q);
>   	unsigned int nr_vecs = iov_iter_npages(iter, BIO_MAX_VECS);
>   	struct bio *bio;
>   	int ret;
> -	int j;
>   
>   	if (!iov_iter_count(iter))
>   		return -EINVAL;
>   
>   	bio = blk_rq_map_bio_alloc(rq, nr_vecs, gfp_mask);
> -	if (bio == NULL)
> +	if (!bio)
>   		return -ENOMEM;
> -
> -	if (blk_queue_pci_p2pdma(rq->q))
> -		extraction_flags |= ITER_ALLOW_P2PDMA;
> -	if (iov_iter_extract_will_pin(iter))
> -		bio_set_flag(bio, BIO_PAGE_PINNED);
> -
> -	while (iov_iter_count(iter)) {
> -		struct page *stack_pages[UIO_FASTIOV];
> -		struct page **pages = stack_pages;
> -		ssize_t bytes;
> -		size_t offs;
> -		int npages;
> -
> -		if (nr_vecs > ARRAY_SIZE(stack_pages))
> -			pages = NULL;
> -
> -		bytes = iov_iter_extract_pages(iter, &pages, LONG_MAX,
> -					       nr_vecs, extraction_flags, &offs);
> -		if (unlikely(bytes <= 0)) {
> -			ret = bytes ? bytes : -EFAULT;
> -			goto out_unmap;
> -		}
> -
> -		npages = DIV_ROUND_UP(offs + bytes, PAGE_SIZE);
> -
> -		if (unlikely(offs & queue_dma_alignment(rq->q)))
> -			j = 0;
> -		else {
> -			for (j = 0; j < npages; j++) {
> -				struct page *page = pages[j];
> -				unsigned int n = PAGE_SIZE - offs;
> -				bool same_page = false;
> -
> -				if (n > bytes)
> -					n = bytes;
> -
> -				if (!bio_add_hw_page(rq->q, bio, page, n, offs,
> -						     max_sectors, &same_page))
> -					break;
> -
> -				if (same_page)
> -					bio_release_page(bio, page);
> -				bytes -= n;
> -				offs = 0;
> -			}
> -		}
> -		/*
> -		 * release the pages we didn't map into the bio, if any
> -		 */
> -		while (j < npages)
> -			bio_release_page(bio, pages[j++]);
> -		if (pages != stack_pages)
> -			kvfree(pages);
> -		/* couldn't stuff something into bio? */
> -		if (bytes) {
> -			iov_iter_revert(iter, bytes);
> -			break;
> -		}
> -	}
> -
> +	ret = bio_iov_iter_get_pages(bio, iter);
> +	if (ret)
> +		goto out_put;

This looks like a more involved change than converting bio_add_hw_page. 
Perhaps should go into a separate patch? Other than that, looks good 
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

Re: [PATCH 2/2] block: remove blk_rq_bio_prep

[Sagi Grimberg]

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

Re: simplify passthrough bio handling

[Jens Axboe]

On Fri, 03 Jan 2025 08:33:56 +0100, Christoph Hellwig wrote:
> this series removes the special casing when adding pages to passthrough
> bios in favor of simply checking that they match the queue limits once
> before submissions.  This mirrors where the zone append users have been
> moving and a recent doing the same for a single optimizes passthrough
> user.
> 
> Diffstat:
>  block/bio.c                        |  107 +-----------------------------
>  block/blk-map.c                    |  128 ++++++++++---------------------------
>  block/blk-mq.c                     |    4 -
>  block/blk.h                        |    8 --
>  drivers/nvme/target/passthru.c     |   18 +++--
>  drivers/nvme/target/zns.c          |    3
>  drivers/target/target_core_pscsi.c |    6 -
>  include/linux/bio.h                |    2
>  include/linux/blk-mq.h             |    8 --
>  9 files changed, 57 insertions(+), 227 deletions(-)
> 
> [...]

Applied, thanks!

[1/2] block: remove bio_add_pc_page
      commit: 6aeb4f836480617be472de767c4cb09c1060a067
[2/2] block: remove blk_rq_bio_prep
      commit: 02ee5d69e3baf2796ba75b928fcbc9cf7884c5e9

Best regards,
-- 
Jens Axboe

Re: [PATCH 1/2] block: remove bio_add_pc_page

[Chaitanya Kulkarni]

On 1/2/25 23:33, Christoph Hellwig wrote:
> Lift bio_split_rw_at into blk_rq_append_bio so that it validates the
> hardware limits.  With this all passthrough callers can simply add
> bio_add_page to build the bio and delay checking for exceeding of limits
> to this point instead of doing it for each page.
>
> While this looks like adding a new expensive loop over all bio_vecs,
> blk_rq_append_bio is already doing that just to counter the number of
> segments.
>
> Signed-off-by: Christoph Hellwig<hch@lst.de>


Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck

Re: [PATCH 2/2] block: remove blk_rq_bio_prep

[Chaitanya Kulkarni]

On 1/2/25 23:33, Christoph Hellwig wrote:
> There is not real point in a helper just to assign three values to four
> fields, especially when the surrounding code is working on the
> neighbor fields directly.
>
> Signed-off-by: Christoph Hellwig<hch@lst.de>


Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck