Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1190 insertions, 0 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
new file mode 100644
index 0000000000..65e75efa9b
--- /dev/null
+++ b/block/blk-merge.c
@@ -0,0 +1,1190 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Functions related to segment and merge handling
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/blk-integrity.h>
+#include <linux/scatterlist.h>
+#include <linux/part_stat.h>
+#include <linux/blk-cgroup.h>
+
+#include <trace/events/block.h>
+
+#include "blk.h"
+#include "blk-mq-sched.h"
+#include "blk-rq-qos.h"
+#include "blk-throttle.h"
+
+static inline void bio_get_first_bvec(struct bio *bio, struct bio_vec *bv)
+{
+	*bv = mp_bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
+}
+
+static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
+{
+	struct bvec_iter iter = bio->bi_iter;
+	int idx;
+
+	bio_get_first_bvec(bio, bv);
+	if (bv->bv_len == bio->bi_iter.bi_size)
+		return;		/* this bio only has a single bvec */
+
+	bio_advance_iter(bio, &iter, iter.bi_size);
+
+	if (!iter.bi_bvec_done)
+		idx = iter.bi_idx - 1;
+	else	/* in the middle of bvec */
+		idx = iter.bi_idx;
+
+	*bv = bio->bi_io_vec[idx];
+
+	/*
+	 * iter.bi_bvec_done records actual length of the last bvec
+	 * if this bio ends in the middle of one io vector
+	 */
+	if (iter.bi_bvec_done)
+		bv->bv_len = iter.bi_bvec_done;
+}
+
+static inline bool bio_will_gap(struct request_queue *q,
+		struct request *prev_rq, struct bio *prev, struct bio *next)
+{
+	struct bio_vec pb, nb;
+
+	if (!bio_has_data(prev) || !queue_virt_boundary(q))
+		return false;
+
+	/*
+	 * Don't merge if the 1st bio starts with non-zero offset, otherwise it
+	 * is quite difficult to respect the sg gap limit.  We work hard to
+	 * merge a huge number of small single bios in case of mkfs.
+	 */
+	if (prev_rq)
+		bio_get_first_bvec(prev_rq->bio, &pb);
+	else
+		bio_get_first_bvec(prev, &pb);
+	if (pb.bv_offset & queue_virt_boundary(q))
+		return true;
+
+	/*
+	 * We don't need to worry about the situation that the merged segment
+	 * ends in unaligned virt boundary:
+	 *
+	 * - if 'pb' ends aligned, the merged segment ends aligned
+	 * - if 'pb' ends unaligned, the next bio must include
+	 *   one single bvec of 'nb', otherwise the 'nb' can't
+	 *   merge with 'pb'
+	 */
+	bio_get_last_bvec(prev, &pb);
+	bio_get_first_bvec(next, &nb);
+	if (biovec_phys_mergeable(q, &pb, &nb))
+		return false;
+	return __bvec_gap_to_prev(&q->limits, &pb, nb.bv_offset);
+}
+
+static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
+{
+	return bio_will_gap(req->q, req, req->biotail, bio);
+}
+
+static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
+{
+	return bio_will_gap(req->q, NULL, bio, req->bio);
+}
+
+/*
+ * The max size one bio can handle is UINT_MAX becasue bvec_iter.bi_size
+ * is defined as 'unsigned int', meantime it has to be aligned to with the
+ * logical block size, which is the minimum accepted unit by hardware.
+ */
+static unsigned int bio_allowed_max_sectors(const struct queue_limits *lim)
+{
+	return round_down(UINT_MAX, lim->logical_block_size) >> SECTOR_SHIFT;
+}
+
+static struct bio *bio_split_discard(struct bio *bio,
+				     const struct queue_limits *lim,
+				     unsigned *nsegs, struct bio_set *bs)
+{
+	unsigned int max_discard_sectors, granularity;
+	sector_t tmp;
+	unsigned split_sectors;
+
+	*nsegs = 1;
+
+	/* Zero-sector (unknown) and one-sector granularities are the same.  */
+	granularity = max(lim->discard_granularity >> 9, 1U);
+
+	max_discard_sectors =
+		min(lim->max_discard_sectors, bio_allowed_max_sectors(lim));
+	max_discard_sectors -= max_discard_sectors % granularity;
+
+	if (unlikely(!max_discard_sectors)) {
+		/* XXX: warn */
+		return NULL;
+	}
+
+	if (bio_sectors(bio) <= max_discard_sectors)
+		return NULL;
+
+	split_sectors = max_discard_sectors;
+
+	/*
+	 * If the next starting sector would be misaligned, stop the discard at
+	 * the previous aligned sector.
+	 */
+	tmp = bio->bi_iter.bi_sector + split_sectors -
+		((lim->discard_alignment >> 9) % granularity);
+	tmp = sector_div(tmp, granularity);
+
+	if (split_sectors > tmp)
+		split_sectors -= tmp;
+
+	return bio_split(bio, split_sectors, GFP_NOIO, bs);
+}
+
+static struct bio *bio_split_write_zeroes(struct bio *bio,
+					  const struct queue_limits *lim,
+					  unsigned *nsegs, struct bio_set *bs)
+{
+	*nsegs = 0;
+	if (!lim->max_write_zeroes_sectors)
+		return NULL;
+	if (bio_sectors(bio) <= lim->max_write_zeroes_sectors)
+		return NULL;
+	return bio_split(bio, lim->max_write_zeroes_sectors, GFP_NOIO, bs);
+}
+
+/*
+ * Return the maximum number of sectors from the start of a bio that may be
+ * submitted as a single request to a block device. If enough sectors remain,
+ * align the end to the physical block size. Otherwise align the end to the
+ * logical block size. This approach minimizes the number of non-aligned
+ * requests that are submitted to a block device if the start of a bio is not
+ * aligned to a physical block boundary.
+ */
+static inline unsigned get_max_io_size(struct bio *bio,
+				       const struct queue_limits *lim)
+{
+	unsigned pbs = lim->physical_block_size >> SECTOR_SHIFT;
+	unsigned lbs = lim->logical_block_size >> SECTOR_SHIFT;
+	unsigned max_sectors = lim->max_sectors, start, end;
+
+	if (lim->chunk_sectors) {
+		max_sectors = min(max_sectors,
+			blk_chunk_sectors_left(bio->bi_iter.bi_sector,
+					       lim->chunk_sectors));
+	}
+
+	start = bio->bi_iter.bi_sector & (pbs - 1);
+	end = (start + max_sectors) & ~(pbs - 1);
+	if (end > start)
+		return end - start;
+	return max_sectors & ~(lbs - 1);
+}
+
+/**
+ * get_max_segment_size() - maximum number of bytes to add as a single segment
+ * @lim: Request queue limits.
+ * @start_page: See below.
+ * @offset: Offset from @start_page where to add a segment.
+ *
+ * Returns the maximum number of bytes that can be added as a single segment.
+ */
+static inline unsigned get_max_segment_size(const struct queue_limits *lim,
+		struct page *start_page, unsigned long offset)
+{
+	unsigned long mask = lim->seg_boundary_mask;
+
+	offset = mask & (page_to_phys(start_page) + offset);
+
+	/*
+	 * Prevent an overflow if mask = ULONG_MAX and offset = 0 by adding 1
+	 * after having calculated the minimum.
+	 */
+	return min(mask - offset, (unsigned long)lim->max_segment_size - 1) + 1;
+}
+
+/**
+ * bvec_split_segs - verify whether or not a bvec should be split in the middle
+ * @lim:      [in] queue limits to split based on
+ * @bv:       [in] bvec to examine
+ * @nsegs:    [in,out] Number of segments in the bio being built. Incremented
+ *            by the number of segments from @bv that may be appended to that
+ *            bio without exceeding @max_segs
+ * @bytes:    [in,out] Number of bytes in the bio being built. Incremented
+ *            by the number of bytes from @bv that may be appended to that
+ *            bio without exceeding @max_bytes
+ * @max_segs: [in] upper bound for *@nsegs
+ * @max_bytes: [in] upper bound for *@bytes
+ *
+ * When splitting a bio, it can happen that a bvec is encountered that is too
+ * big to fit in a single segment and hence that it has to be split in the
+ * middle. This function verifies whether or not that should happen. The value
+ * %true is returned if and only if appending the entire @bv to a bio with
+ * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
+ * the block driver.
+ */
+static bool bvec_split_segs(const struct queue_limits *lim,
+		const struct bio_vec *bv, unsigned *nsegs, unsigned *bytes,
+		unsigned max_segs, unsigned max_bytes)
+{
+	unsigned max_len = min(max_bytes, UINT_MAX) - *bytes;
+	unsigned len = min(bv->bv_len, max_len);
+	unsigned total_len = 0;
+	unsigned seg_size = 0;
+
+	while (len && *nsegs < max_segs) {
+		seg_size = get_max_segment_size(lim, bv->bv_page,
+						bv->bv_offset + total_len);
+		seg_size = min(seg_size, len);
+
+		(*nsegs)++;
+		total_len += seg_size;
+		len -= seg_size;
+
+		if ((bv->bv_offset + total_len) & lim->virt_boundary_mask)
+			break;
+	}
+
+	*bytes += total_len;
+
+	/* tell the caller to split the bvec if it is too big to fit */
+	return len > 0 || bv->bv_len > max_len;
+}
+
+/**
+ * bio_split_rw - split a bio in two bios
+ * @bio:  [in] bio to be split
+ * @lim:  [in] queue limits to split based on
+ * @segs: [out] number of segments in the bio with the first half of the sectors
+ * @bs:	  [in] bio set to allocate the clone from
+ * @max_bytes: [in] maximum number of bytes per bio
+ *
+ * Clone @bio, update the bi_iter of the clone to represent the first sectors
+ * of @bio and update @bio->bi_iter to represent the remaining sectors. The
+ * following is guaranteed for the cloned bio:
+ * - That it has at most @max_bytes worth of data
+ * - That it has at most queue_max_segments(@q) segments.
+ *
+ * Except for discard requests the cloned bio will point at the bi_io_vec of
+ * the original bio. It is the responsibility of the caller to ensure that the
+ * original bio is not freed before the cloned bio. The caller is also
+ * responsible for ensuring that @bs is only destroyed after processing of the
+ * split bio has finished.
+ */
+struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
+		unsigned *segs, struct bio_set *bs, unsigned max_bytes)
+{
+	struct bio_vec bv, bvprv, *bvprvp = NULL;
+	struct bvec_iter iter;
+	unsigned nsegs = 0, bytes = 0;
+
+	bio_for_each_bvec(bv, bio, iter) {
+		/*
+		 * If the queue doesn't support SG gaps and adding this
+		 * offset would create a gap, disallow it.
+		 */
+		if (bvprvp && bvec_gap_to_prev(lim, bvprvp, bv.bv_offset))
+			goto split;
+
+		if (nsegs < lim->max_segments &&
+		    bytes + bv.bv_len <= max_bytes &&
+		    bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
+			nsegs++;
+			bytes += bv.bv_len;
+		} else {
+			if (bvec_split_segs(lim, &bv, &nsegs, &bytes,
+					lim->max_segments, max_bytes))
+				goto split;
+		}
+
+		bvprv = bv;
+		bvprvp = &bvprv;
+	}
+
+	*segs = nsegs;
+	return NULL;
+split:
+	/*
+	 * We can't sanely support splitting for a REQ_NOWAIT bio. End it
+	 * with EAGAIN if splitting is required and return an error pointer.
+	 */
+	if (bio->bi_opf & REQ_NOWAIT) {
+		bio->bi_status = BLK_STS_AGAIN;
+		bio_endio(bio);
+		return ERR_PTR(-EAGAIN);
+	}
+
+	*segs = nsegs;
+
+	/*
+	 * Individual bvecs might not be logical block aligned. Round down the
+	 * split size so that each bio is properly block size aligned, even if
+	 * we do not use the full hardware limits.
+	 */
+	bytes = ALIGN_DOWN(bytes, lim->logical_block_size);
+
+	/*
+	 * Bio splitting may cause subtle trouble such as hang when doing sync
+	 * iopoll in direct IO routine. Given performance gain of iopoll for
+	 * big IO can be trival, disable iopoll when split needed.
+	 */
+	bio_clear_polled(bio);
+	return bio_split(bio, bytes >> SECTOR_SHIFT, GFP_NOIO, bs);
+}
+EXPORT_SYMBOL_GPL(bio_split_rw);
+
+/**
+ * __bio_split_to_limits - split a bio to fit the queue limits
+ * @bio:     bio to be split
+ * @lim:     queue limits to split based on
+ * @nr_segs: returns the number of segments in the returned bio
+ *
+ * Check if @bio needs splitting based on the queue limits, and if so split off
+ * a bio fitting the limits from the beginning of @bio and return it.  @bio is
+ * shortened to the remainder and re-submitted.
+ *
+ * The split bio is allocated from @q->bio_split, which is provided by the
+ * block layer.
+ */
+struct bio *__bio_split_to_limits(struct bio *bio,
+				  const struct queue_limits *lim,
+				  unsigned int *nr_segs)
+{
+	struct bio_set *bs = &bio->bi_bdev->bd_disk->bio_split;
+	struct bio *split;
+
+	switch (bio_op(bio)) {
+	case REQ_OP_DISCARD:
+	case REQ_OP_SECURE_ERASE:
+		split = bio_split_discard(bio, lim, nr_segs, bs);
+		break;
+	case REQ_OP_WRITE_ZEROES:
+		split = bio_split_write_zeroes(bio, lim, nr_segs, bs);
+		break;
+	default:
+		split = bio_split_rw(bio, lim, nr_segs, bs,
+				get_max_io_size(bio, lim) << SECTOR_SHIFT);
+		if (IS_ERR(split))
+			return NULL;
+		break;
+	}
+
+	if (split) {
+		/* there isn't chance to merge the split bio */
+		split->bi_opf |= REQ_NOMERGE;
+
+		blkcg_bio_issue_init(split);
+		bio_chain(split, bio);
+		trace_block_split(split, bio->bi_iter.bi_sector);
+		submit_bio_noacct(bio);
+		return split;
+	}
+	return bio;
+}
+
+/**
+ * bio_split_to_limits - split a bio to fit the queue limits
+ * @bio:     bio to be split
+ *
+ * Check if @bio needs splitting based on the queue limits of @bio->bi_bdev, and
+ * if so split off a bio fitting the limits from the beginning of @bio and
+ * return it.  @bio is shortened to the remainder and re-submitted.
+ *
+ * The split bio is allocated from @q->bio_split, which is provided by the
+ * block layer.
+ */
+struct bio *bio_split_to_limits(struct bio *bio)
+{
+	const struct queue_limits *lim = &bdev_get_queue(bio->bi_bdev)->limits;
+	unsigned int nr_segs;
+
+	if (bio_may_exceed_limits(bio, lim))
+		return __bio_split_to_limits(bio, lim, &nr_segs);
+	return bio;
+}
+EXPORT_SYMBOL(bio_split_to_limits);
+
+unsigned int blk_recalc_rq_segments(struct request *rq)
+{
+	unsigned int nr_phys_segs = 0;
+	unsigned int bytes = 0;
+	struct req_iterator iter;
+	struct bio_vec bv;
+
+	if (!rq->bio)
+		return 0;
+
+	switch (bio_op(rq->bio)) {
+	case REQ_OP_DISCARD:
+	case REQ_OP_SECURE_ERASE:
+		if (queue_max_discard_segments(rq->q) > 1) {
+			struct bio *bio = rq->bio;
+
+			for_each_bio(bio)
+				nr_phys_segs++;
+			return nr_phys_segs;
+		}
+		return 1;
+	case REQ_OP_WRITE_ZEROES:
+		return 0;
+	default:
+		break;
+	}
+
+	rq_for_each_bvec(bv, rq, iter)
+		bvec_split_segs(&rq->q->limits, &bv, &nr_phys_segs, &bytes,
+				UINT_MAX, UINT_MAX);
+	return nr_phys_segs;
+}
+
+static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
+		struct scatterlist *sglist)
+{
+	if (!*sg)
+		return sglist;
+
+	/*
+	 * If the driver previously mapped a shorter list, we could see a
+	 * termination bit prematurely unless it fully inits the sg table
+	 * on each mapping. We KNOW that there must be more entries here
+	 * or the driver would be buggy, so force clear the termination bit
+	 * to avoid doing a full sg_init_table() in drivers for each command.
+	 */
+	sg_unmark_end(*sg);
+	return sg_next(*sg);
+}
+
+static unsigned blk_bvec_map_sg(struct request_queue *q,
+		struct bio_vec *bvec, struct scatterlist *sglist,
+		struct scatterlist **sg)
+{
+	unsigned nbytes = bvec->bv_len;
+	unsigned nsegs = 0, total = 0;
+
+	while (nbytes > 0) {
+		unsigned offset = bvec->bv_offset + total;
+		unsigned len = min(get_max_segment_size(&q->limits,
+				   bvec->bv_page, offset), nbytes);
+		struct page *page = bvec->bv_page;
+
+		/*
+		 * Unfortunately a fair number of drivers barf on scatterlists
+		 * that have an offset larger than PAGE_SIZE, despite other
+		 * subsystems dealing with that invariant just fine.  For now
+		 * stick to the legacy format where we never present those from
+		 * the block layer, but the code below should be removed once
+		 * these offenders (mostly MMC/SD drivers) are fixed.
+		 */
+		page += (offset >> PAGE_SHIFT);
+		offset &= ~PAGE_MASK;
+
+		*sg = blk_next_sg(sg, sglist);
+		sg_set_page(*sg, page, len, offset);
+
+		total += len;
+		nbytes -= len;
+		nsegs++;
+	}
+
+	return nsegs;
+}
+
+static inline int __blk_bvec_map_sg(struct bio_vec bv,
+		struct scatterlist *sglist, struct scatterlist **sg)
+{
+	*sg = blk_next_sg(sg, sglist);
+	sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
+	return 1;
+}
+
+/* only try to merge bvecs into one sg if they are from two bios */
+static inline bool
+__blk_segment_map_sg_merge(struct request_queue *q, struct bio_vec *bvec,
+			   struct bio_vec *bvprv, struct scatterlist **sg)
+{
+
+	int nbytes = bvec->bv_len;
+
+	if (!*sg)
+		return false;
+
+	if ((*sg)->length + nbytes > queue_max_segment_size(q))
+		return false;
+
+	if (!biovec_phys_mergeable(q, bvprv, bvec))
+		return false;
+
+	(*sg)->length += nbytes;
+
+	return true;
+}
+
+static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
+			     struct scatterlist *sglist,
+			     struct scatterlist **sg)
+{
+	struct bio_vec bvec, bvprv = { NULL };
+	struct bvec_iter iter;
+	int nsegs = 0;
+	bool new_bio = false;
+
+	for_each_bio(bio) {
+		bio_for_each_bvec(bvec, bio, iter) {
+			/*
+			 * Only try to merge bvecs from two bios given we
+			 * have done bio internal merge when adding pages
+			 * to bio
+			 */
+			if (new_bio &&
+			    __blk_segment_map_sg_merge(q, &bvec, &bvprv, sg))
+				goto next_bvec;
+
+			if (bvec.bv_offset + bvec.bv_len <= PAGE_SIZE)
+				nsegs += __blk_bvec_map_sg(bvec, sglist, sg);
+			else
+				nsegs += blk_bvec_map_sg(q, &bvec, sglist, sg);
+ next_bvec:
+			new_bio = false;
+		}
+		if (likely(bio->bi_iter.bi_size)) {
+			bvprv = bvec;
+			new_bio = true;
+		}
+	}
+
+	return nsegs;
+}
+
+/*
+ * map a request to scatterlist, return number of sg entries setup. Caller
+ * must make sure sg can hold rq->nr_phys_segments entries
+ */
+int __blk_rq_map_sg(struct request_queue *q, struct request *rq,
+		struct scatterlist *sglist, struct scatterlist **last_sg)
+{
+	int nsegs = 0;
+
+	if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
+		nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, last_sg);
+	else if (rq->bio)
+		nsegs = __blk_bios_map_sg(q, rq->bio, sglist, last_sg);
+
+	if (*last_sg)
+		sg_mark_end(*last_sg);
+
+	/*
+	 * Something must have been wrong if the figured number of
+	 * segment is bigger than number of req's physical segments
+	 */
+	WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
+
+	return nsegs;
+}
+EXPORT_SYMBOL(__blk_rq_map_sg);
+
+static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
+						  sector_t offset)
+{
+	struct request_queue *q = rq->q;
+	unsigned int max_sectors;
+
+	if (blk_rq_is_passthrough(rq))
+		return q->limits.max_hw_sectors;
+
+	max_sectors = blk_queue_get_max_sectors(q, req_op(rq));
+	if (!q->limits.chunk_sectors ||
+	    req_op(rq) == REQ_OP_DISCARD ||
+	    req_op(rq) == REQ_OP_SECURE_ERASE)
+		return max_sectors;
+	return min(max_sectors,
+		   blk_chunk_sectors_left(offset, q->limits.chunk_sectors));
+}
+
+static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
+		unsigned int nr_phys_segs)
+{
+	if (!blk_cgroup_mergeable(req, bio))
+		goto no_merge;
+
+	if (blk_integrity_merge_bio(req->q, req, bio) == false)
+		goto no_merge;
+
+	/* discard request merge won't add new segment */
+	if (req_op(req) == REQ_OP_DISCARD)
+		return 1;
+
+	if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
+		goto no_merge;
+
+	/*
+	 * This will form the start of a new hw segment.  Bump both
+	 * counters.
+	 */
+	req->nr_phys_segments += nr_phys_segs;
+	return 1;
+
+no_merge:
+	req_set_nomerge(req->q, req);
+	return 0;
+}
+
+int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
+{
+	if (req_gap_back_merge(req, bio))
+		return 0;
+	if (blk_integrity_rq(req) &&
+	    integrity_req_gap_back_merge(req, bio))
+		return 0;
+	if (!bio_crypt_ctx_back_mergeable(req, bio))
+		return 0;
+	if (blk_rq_sectors(req) + bio_sectors(bio) >
+	    blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
+		req_set_nomerge(req->q, req);
+		return 0;
+	}
+
+	return ll_new_hw_segment(req, bio, nr_segs);
+}
+
+static int ll_front_merge_fn(struct request *req, struct bio *bio,
+		unsigned int nr_segs)
+{
+	if (req_gap_front_merge(req, bio))
+		return 0;
+	if (blk_integrity_rq(req) &&
+	    integrity_req_gap_front_merge(req, bio))
+		return 0;
+	if (!bio_crypt_ctx_front_mergeable(req, bio))
+		return 0;
+	if (blk_rq_sectors(req) + bio_sectors(bio) >
+	    blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
+		req_set_nomerge(req->q, req);
+		return 0;
+	}
+
+	return ll_new_hw_segment(req, bio, nr_segs);
+}
+
+static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
+		struct request *next)
+{
+	unsigned short segments = blk_rq_nr_discard_segments(req);
+
+	if (segments >= queue_max_discard_segments(q))
+		goto no_merge;
+	if (blk_rq_sectors(req) + bio_sectors(next->bio) >
+	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
+		goto no_merge;
+
+	req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
+	return true;
+no_merge:
+	req_set_nomerge(q, req);
+	return false;
+}
+
+static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
+				struct request *next)
+{
+	int total_phys_segments;
+
+	if (req_gap_back_merge(req, next->bio))
+		return 0;
+
+	/*
+	 * Will it become too large?
+	 */
+	if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
+	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
+		return 0;
+
+	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
+	if (total_phys_segments > blk_rq_get_max_segments(req))
+		return 0;
+
+	if (!blk_cgroup_mergeable(req, next->bio))
+		return 0;
+
+	if (blk_integrity_merge_rq(q, req, next) == false)
+		return 0;
+
+	if (!bio_crypt_ctx_merge_rq(req, next))
+		return 0;
+
+	/* Merge is OK... */
+	req->nr_phys_segments = total_phys_segments;
+	return 1;
+}
+
+/**
+ * blk_rq_set_mixed_merge - mark a request as mixed merge
+ * @rq: request to mark as mixed merge
+ *
+ * Description:
+ *     @rq is about to be mixed merged.  Make sure the attributes
+ *     which can be mixed are set in each bio and mark @rq as mixed
+ *     merged.
+ */
+void blk_rq_set_mixed_merge(struct request *rq)
+{
+	blk_opf_t ff = rq->cmd_flags & REQ_FAILFAST_MASK;
+	struct bio *bio;
+
+	if (rq->rq_flags & RQF_MIXED_MERGE)
+		return;
+
+	/*
+	 * @rq will no longer represent mixable attributes for all the
+	 * contained bios.  It will just track those of the first one.
+	 * Distributes the attributs to each bio.
+	 */
+	for (bio = rq->bio; bio; bio = bio->bi_next) {
+		WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
+			     (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
+		bio->bi_opf |= ff;
+	}
+	rq->rq_flags |= RQF_MIXED_MERGE;
+}
+
+static inline blk_opf_t bio_failfast(const struct bio *bio)
+{
+	if (bio->bi_opf & REQ_RAHEAD)
+		return REQ_FAILFAST_MASK;
+
+	return bio->bi_opf & REQ_FAILFAST_MASK;
+}
+
+/*
+ * After we are marked as MIXED_MERGE, any new RA bio has to be updated
+ * as failfast, and request's failfast has to be updated in case of
+ * front merge.
+ */
+static inline void blk_update_mixed_merge(struct request *req,
+		struct bio *bio, bool front_merge)
+{
+	if (req->rq_flags & RQF_MIXED_MERGE) {
+		if (bio->bi_opf & REQ_RAHEAD)
+			bio->bi_opf |= REQ_FAILFAST_MASK;
+
+		if (front_merge) {
+			req->cmd_flags &= ~REQ_FAILFAST_MASK;
+			req->cmd_flags |= bio->bi_opf & REQ_FAILFAST_MASK;
+		}
+	}
+}
+
+static void blk_account_io_merge_request(struct request *req)
+{
+	if (blk_do_io_stat(req)) {
+		part_stat_lock();
+		part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
+		part_stat_unlock();
+	}
+}
+
+static enum elv_merge blk_try_req_merge(struct request *req,
+					struct request *next)
+{
+	if (blk_discard_mergable(req))
+		return ELEVATOR_DISCARD_MERGE;
+	else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
+		return ELEVATOR_BACK_MERGE;
+
+	return ELEVATOR_NO_MERGE;
+}
+
+/*
+ * For non-mq, this has to be called with the request spinlock acquired.
+ * For mq with scheduling, the appropriate queue wide lock should be held.
+ */
+static struct request *attempt_merge(struct request_queue *q,
+				     struct request *req, struct request *next)
+{
+	if (!rq_mergeable(req) || !rq_mergeable(next))
+		return NULL;
+
+	if (req_op(req) != req_op(next))
+		return NULL;
+
+	if (rq_data_dir(req) != rq_data_dir(next))
+		return NULL;
+
+	if (req->ioprio != next->ioprio)
+		return NULL;
+
+	/*
+	 * If we are allowed to merge, then append bio list
+	 * from next to rq and release next. merge_requests_fn
+	 * will have updated segment counts, update sector
+	 * counts here. Handle DISCARDs separately, as they
+	 * have separate settings.
+	 */
+
+	switch (blk_try_req_merge(req, next)) {
+	case ELEVATOR_DISCARD_MERGE:
+		if (!req_attempt_discard_merge(q, req, next))
+			return NULL;
+		break;
+	case ELEVATOR_BACK_MERGE:
+		if (!ll_merge_requests_fn(q, req, next))
+			return NULL;
+		break;
+	default:
+		return NULL;
+	}
+
+	/*
+	 * If failfast settings disagree or any of the two is already
+	 * a mixed merge, mark both as mixed before proceeding.  This
+	 * makes sure that all involved bios have mixable attributes
+	 * set properly.
+	 */
+	if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
+	    (req->cmd_flags & REQ_FAILFAST_MASK) !=
+	    (next->cmd_flags & REQ_FAILFAST_MASK)) {
+		blk_rq_set_mixed_merge(req);
+		blk_rq_set_mixed_merge(next);
+	}
+
+	/*
+	 * At this point we have either done a back merge or front merge. We
+	 * need the smaller start_time_ns of the merged requests to be the
+	 * current request for accounting purposes.
+	 */
+	if (next->start_time_ns < req->start_time_ns)
+		req->start_time_ns = next->start_time_ns;
+
+	req->biotail->bi_next = next->bio;
+	req->biotail = next->biotail;
+
+	req->__data_len += blk_rq_bytes(next);
+
+	if (!blk_discard_mergable(req))
+		elv_merge_requests(q, req, next);
+
+	blk_crypto_rq_put_keyslot(next);
+
+	/*
+	 * 'next' is going away, so update stats accordingly
+	 */
+	blk_account_io_merge_request(next);
+
+	trace_block_rq_merge(next);
+
+	/*
+	 * ownership of bio passed from next to req, return 'next' for
+	 * the caller to free
+	 */
+	next->bio = NULL;
+	return next;
+}
+
+static struct request *attempt_back_merge(struct request_queue *q,
+		struct request *rq)
+{
+	struct request *next = elv_latter_request(q, rq);
+
+	if (next)
+		return attempt_merge(q, rq, next);
+
+	return NULL;
+}
+
+static struct request *attempt_front_merge(struct request_queue *q,
+		struct request *rq)
+{
+	struct request *prev = elv_former_request(q, rq);
+
+	if (prev)
+		return attempt_merge(q, prev, rq);
+
+	return NULL;
+}
+
+/*
+ * Try to merge 'next' into 'rq'. Return true if the merge happened, false
+ * otherwise. The caller is responsible for freeing 'next' if the merge
+ * happened.
+ */
+bool blk_attempt_req_merge(struct request_queue *q, struct request *rq,
+			   struct request *next)
+{
+	return attempt_merge(q, rq, next);
+}
+
+bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
+{
+	if (!rq_mergeable(rq) || !bio_mergeable(bio))
+		return false;
+
+	if (req_op(rq) != bio_op(bio))
+		return false;
+
+	/* different data direction or already started, don't merge */
+	if (bio_data_dir(bio) != rq_data_dir(rq))
+		return false;
+
+	/* don't merge across cgroup boundaries */
+	if (!blk_cgroup_mergeable(rq, bio))
+		return false;
+
+	/* only merge integrity protected bio into ditto rq */
+	if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
+		return false;
+
+	/* Only merge if the crypt contexts are compatible */
+	if (!bio_crypt_rq_ctx_compatible(rq, bio))
+		return false;
+
+	if (rq->ioprio != bio_prio(bio))
+		return false;
+
+	return true;
+}
+
+enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
+{
+	if (blk_discard_mergable(rq))
+		return ELEVATOR_DISCARD_MERGE;
+	else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
+		return ELEVATOR_BACK_MERGE;
+	else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
+		return ELEVATOR_FRONT_MERGE;
+	return ELEVATOR_NO_MERGE;
+}
+
+static void blk_account_io_merge_bio(struct request *req)
+{
+	if (!blk_do_io_stat(req))
+		return;
+
+	part_stat_lock();
+	part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
+	part_stat_unlock();
+}
+
+enum bio_merge_status {
+	BIO_MERGE_OK,
+	BIO_MERGE_NONE,
+	BIO_MERGE_FAILED,
+};
+
+static enum bio_merge_status bio_attempt_back_merge(struct request *req,
+		struct bio *bio, unsigned int nr_segs)
+{
+	const blk_opf_t ff = bio_failfast(bio);
+
+	if (!ll_back_merge_fn(req, bio, nr_segs))
+		return BIO_MERGE_FAILED;
+
+	trace_block_bio_backmerge(bio);
+	rq_qos_merge(req->q, req, bio);
+
+	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
+		blk_rq_set_mixed_merge(req);
+
+	blk_update_mixed_merge(req, bio, false);
+
+	req->biotail->bi_next = bio;
+	req->biotail = bio;
+	req->__data_len += bio->bi_iter.bi_size;
+
+	bio_crypt_free_ctx(bio);
+
+	blk_account_io_merge_bio(req);
+	return BIO_MERGE_OK;
+}
+
+static enum bio_merge_status bio_attempt_front_merge(struct request *req,
+		struct bio *bio, unsigned int nr_segs)
+{
+	const blk_opf_t ff = bio_failfast(bio);
+
+	if (!ll_front_merge_fn(req, bio, nr_segs))
+		return BIO_MERGE_FAILED;
+
+	trace_block_bio_frontmerge(bio);
+	rq_qos_merge(req->q, req, bio);
+
+	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
+		blk_rq_set_mixed_merge(req);
+
+	blk_update_mixed_merge(req, bio, true);
+
+	bio->bi_next = req->bio;
+	req->bio = bio;
+
+	req->__sector = bio->bi_iter.bi_sector;
+	req->__data_len += bio->bi_iter.bi_size;
+
+	bio_crypt_do_front_merge(req, bio);
+
+	blk_account_io_merge_bio(req);
+	return BIO_MERGE_OK;
+}
+
+static enum bio_merge_status bio_attempt_discard_merge(struct request_queue *q,
+		struct request *req, struct bio *bio)
+{
+	unsigned short segments = blk_rq_nr_discard_segments(req);
+
+	if (segments >= queue_max_discard_segments(q))
+		goto no_merge;
+	if (blk_rq_sectors(req) + bio_sectors(bio) >
+	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
+		goto no_merge;
+
+	rq_qos_merge(q, req, bio);
+
+	req->biotail->bi_next = bio;
+	req->biotail = bio;
+	req->__data_len += bio->bi_iter.bi_size;
+	req->nr_phys_segments = segments + 1;
+
+	blk_account_io_merge_bio(req);
+	return BIO_MERGE_OK;
+no_merge:
+	req_set_nomerge(q, req);
+	return BIO_MERGE_FAILED;
+}
+
+static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
+						   struct request *rq,
+						   struct bio *bio,
+						   unsigned int nr_segs,
+						   bool sched_allow_merge)
+{
+	if (!blk_rq_merge_ok(rq, bio))
+		return BIO_MERGE_NONE;
+
+	switch (blk_try_merge(rq, bio)) {
+	case ELEVATOR_BACK_MERGE:
+		if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
+			return bio_attempt_back_merge(rq, bio, nr_segs);
+		break;
+	case ELEVATOR_FRONT_MERGE:
+		if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
+			return bio_attempt_front_merge(rq, bio, nr_segs);
+		break;
+	case ELEVATOR_DISCARD_MERGE:
+		return bio_attempt_discard_merge(q, rq, bio);
+	default:
+		return BIO_MERGE_NONE;
+	}
+
+	return BIO_MERGE_FAILED;
+}
+
+/**
+ * blk_attempt_plug_merge - try to merge with %current's plugged list
+ * @q: request_queue new bio is being queued at
+ * @bio: new bio being queued
+ * @nr_segs: number of segments in @bio
+ * from the passed in @q already in the plug list
+ *
+ * Determine whether @bio being queued on @q can be merged with the previous
+ * request on %current's plugged list.  Returns %true if merge was successful,
+ * otherwise %false.
+ *
+ * Plugging coalesces IOs from the same issuer for the same purpose without
+ * going through @q->queue_lock.  As such it's more of an issuing mechanism
+ * than scheduling, and the request, while may have elvpriv data, is not
+ * added on the elevator at this point.  In addition, we don't have
+ * reliable access to the elevator outside queue lock.  Only check basic
+ * merging parameters without querying the elevator.
+ *
+ * Caller must ensure !blk_queue_nomerges(q) beforehand.
+ */
+bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
+		unsigned int nr_segs)
+{
+	struct blk_plug *plug;
+	struct request *rq;
+
+	plug = blk_mq_plug(bio);
+	if (!plug || rq_list_empty(plug->mq_list))
+		return false;
+
+	rq_list_for_each(&plug->mq_list, rq) {
+		if (rq->q == q) {
+			if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
+			    BIO_MERGE_OK)
+				return true;
+			break;
+		}
+
+		/*
+		 * Only keep iterating plug list for merges if we have multiple
+		 * queues
+		 */
+		if (!plug->multiple_queues)
+			break;
+	}
+	return false;
+}
+
+/*
+ * Iterate list of requests and see if we can merge this bio with any
+ * of them.
+ */
+bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,
+			struct bio *bio, unsigned int nr_segs)
+{
+	struct request *rq;
+	int checked = 8;
+
+	list_for_each_entry_reverse(rq, list, queuelist) {
+		if (!checked--)
+			break;
+
+		switch (blk_attempt_bio_merge(q, rq, bio, nr_segs, true)) {
+		case BIO_MERGE_NONE:
+			continue;
+		case BIO_MERGE_OK:
+			return true;
+		case BIO_MERGE_FAILED:
+			return false;
+		}
+
+	}
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(blk_bio_list_merge);
+
+bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
+		unsigned int nr_segs, struct request **merged_request)
+{
+	struct request *rq;
+
+	switch (elv_merge(q, &rq, bio)) {
+	case ELEVATOR_BACK_MERGE:
+		if (!blk_mq_sched_allow_merge(q, rq, bio))
+			return false;
+		if (bio_attempt_back_merge(rq, bio, nr_segs) != BIO_MERGE_OK)
+			return false;
+		*merged_request = attempt_back_merge(q, rq);
+		if (!*merged_request)
+			elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
+		return true;
+	case ELEVATOR_FRONT_MERGE:
+		if (!blk_mq_sched_allow_merge(q, rq, bio))
+			return false;
+		if (bio_attempt_front_merge(rq, bio, nr_segs) != BIO_MERGE_OK)
+			return false;
+		*merged_request = attempt_front_merge(q, rq);
+		if (!*merged_request)
+			elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
+		return true;
+	case ELEVATOR_DISCARD_MERGE:
+		return bio_attempt_discard_merge(q, rq, bio) == BIO_MERGE_OK;
+	default:
+		return false;
+	}
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);