block/blk-merge.c

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This source file includes following definitions.
bio_will_gap
req_gap_back_merge
req_gap_front_merge
blk_bio_discard_split
blk_bio_write_zeroes_split
blk_bio_write_same_split
get_max_io_size
get_max_segment_size
bvec_split_segs
blk_bio_segment_split
__blk_queue_split
blk_queue_split
blk_recalc_rq_segments
blk_next_sg
blk_bvec_map_sg
__blk_bvec_map_sg
__blk_segment_map_sg_merge
__blk_bios_map_sg
blk_rq_map_sg
ll_new_hw_segment
ll_back_merge_fn
ll_front_merge_fn
req_attempt_discard_merge
ll_merge_requests_fn
blk_rq_set_mixed_merge
blk_account_io_merge
blk_discard_mergable
blk_try_req_merge
attempt_merge
attempt_back_merge
attempt_front_merge
blk_attempt_req_merge
blk_rq_merge_ok
blk_try_merge
   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Functions related to segment and merge handling
   4  */
   5 #include <linux/kernel.h>
   6 #include <linux/module.h>
   7 #include <linux/bio.h>
   8 #include <linux/blkdev.h>
   9 #include <linux/scatterlist.h>
  10 
  11 #include <trace/events/block.h>
  12 
  13 #include "blk.h"
  14 
  15 static inline bool bio_will_gap(struct request_queue *q,
  16                 struct request *prev_rq, struct bio *prev, struct bio *next)
  17 {
  18         struct bio_vec pb, nb;
  19 
  20         if (!bio_has_data(prev) || !queue_virt_boundary(q))
  21                 return false;
  22 
  23         /*
  24          * Don't merge if the 1st bio starts with non-zero offset, otherwise it
  25          * is quite difficult to respect the sg gap limit.  We work hard to
  26          * merge a huge number of small single bios in case of mkfs.
  27          */
  28         if (prev_rq)
  29                 bio_get_first_bvec(prev_rq->bio, &pb);
  30         else
  31                 bio_get_first_bvec(prev, &pb);
  32         if (pb.bv_offset & queue_virt_boundary(q))
  33                 return true;
  34 
  35         /*
  36          * We don't need to worry about the situation that the merged segment
  37          * ends in unaligned virt boundary:
  38          *
  39          * - if 'pb' ends aligned, the merged segment ends aligned
  40          * - if 'pb' ends unaligned, the next bio must include
  41          *   one single bvec of 'nb', otherwise the 'nb' can't
  42          *   merge with 'pb'
  43          */
  44         bio_get_last_bvec(prev, &pb);
  45         bio_get_first_bvec(next, &nb);
  46         if (biovec_phys_mergeable(q, &pb, &nb))
  47                 return false;
  48         return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
  49 }
  50 
  51 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
  52 {
  53         return bio_will_gap(req->q, req, req->biotail, bio);
  54 }
  55 
  56 static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
  57 {
  58         return bio_will_gap(req->q, NULL, bio, req->bio);
  59 }
  60 
  61 static struct bio *blk_bio_discard_split(struct request_queue *q,
  62                                          struct bio *bio,
  63                                          struct bio_set *bs,
  64                                          unsigned *nsegs)
  65 {
  66         unsigned int max_discard_sectors, granularity;
  67         int alignment;
  68         sector_t tmp;
  69         unsigned split_sectors;
  70 
  71         *nsegs = 1;
  72 
  73         /* Zero-sector (unknown) and one-sector granularities are the same.  */
  74         granularity = max(q->limits.discard_granularity >> 9, 1U);
  75 
  76         max_discard_sectors = min(q->limits.max_discard_sectors,
  77                         bio_allowed_max_sectors(q));
  78         max_discard_sectors -= max_discard_sectors % granularity;
  79 
  80         if (unlikely(!max_discard_sectors)) {
  81                 /* XXX: warn */
  82                 return NULL;
  83         }
  84 
  85         if (bio_sectors(bio) <= max_discard_sectors)
  86                 return NULL;
  87 
  88         split_sectors = max_discard_sectors;
  89 
  90         /*
  91          * If the next starting sector would be misaligned, stop the discard at
  92          * the previous aligned sector.
  93          */
  94         alignment = (q->limits.discard_alignment >> 9) % granularity;
  95 
  96         tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
  97         tmp = sector_div(tmp, granularity);
  98 
  99         if (split_sectors > tmp)
 100                 split_sectors -= tmp;
 101 
 102         return bio_split(bio, split_sectors, GFP_NOIO, bs);
 103 }
 104 
 105 static struct bio *blk_bio_write_zeroes_split(struct request_queue *q,
 106                 struct bio *bio, struct bio_set *bs, unsigned *nsegs)
 107 {
 108         *nsegs = 0;
 109 
 110         if (!q->limits.max_write_zeroes_sectors)
 111                 return NULL;
 112 
 113         if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
 114                 return NULL;
 115 
 116         return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
 117 }
 118 
 119 static struct bio *blk_bio_write_same_split(struct request_queue *q,
 120                                             struct bio *bio,
 121                                             struct bio_set *bs,
 122                                             unsigned *nsegs)
 123 {
 124         *nsegs = 1;
 125 
 126         if (!q->limits.max_write_same_sectors)
 127                 return NULL;
 128 
 129         if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
 130                 return NULL;
 131 
 132         return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
 133 }
 134 
 135 /*
 136  * Return the maximum number of sectors from the start of a bio that may be
 137  * submitted as a single request to a block device. If enough sectors remain,
 138  * align the end to the physical block size. Otherwise align the end to the
 139  * logical block size. This approach minimizes the number of non-aligned
 140  * requests that are submitted to a block device if the start of a bio is not
 141  * aligned to a physical block boundary.
 142  */
 143 static inline unsigned get_max_io_size(struct request_queue *q,
 144                                        struct bio *bio)
 145 {
 146         unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
 147         unsigned max_sectors = sectors;
 148         unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
 149         unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
 150         unsigned start_offset = bio->bi_iter.bi_sector & (pbs - 1);
 151 
 152         max_sectors += start_offset;
 153         max_sectors &= ~(pbs - 1);
 154         if (max_sectors > start_offset)
 155                 return max_sectors - start_offset;
 156 
 157         return sectors & (lbs - 1);
 158 }
 159 
 160 static unsigned get_max_segment_size(const struct request_queue *q,
 161                                      unsigned offset)
 162 {
 163         unsigned long mask = queue_segment_boundary(q);
 164 
 165         /* default segment boundary mask means no boundary limit */
 166         if (mask == BLK_SEG_BOUNDARY_MASK)
 167                 return queue_max_segment_size(q);
 168 
 169         return min_t(unsigned long, mask - (mask & offset) + 1,
 170                      queue_max_segment_size(q));
 171 }
 172 
 173 /**
 174  * bvec_split_segs - verify whether or not a bvec should be split in the middle
 175  * @q:        [in] request queue associated with the bio associated with @bv
 176  * @bv:       [in] bvec to examine
 177  * @nsegs:    [in,out] Number of segments in the bio being built. Incremented
 178  *            by the number of segments from @bv that may be appended to that
 179  *            bio without exceeding @max_segs
 180  * @sectors:  [in,out] Number of sectors in the bio being built. Incremented
 181  *            by the number of sectors from @bv that may be appended to that
 182  *            bio without exceeding @max_sectors
 183  * @max_segs: [in] upper bound for *@nsegs
 184  * @max_sectors: [in] upper bound for *@sectors
 185  *
 186  * When splitting a bio, it can happen that a bvec is encountered that is too
 187  * big to fit in a single segment and hence that it has to be split in the
 188  * middle. This function verifies whether or not that should happen. The value
 189  * %true is returned if and only if appending the entire @bv to a bio with
 190  * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
 191  * the block driver.
 192  */
 193 static bool bvec_split_segs(const struct request_queue *q,
 194                             const struct bio_vec *bv, unsigned *nsegs,
 195                             unsigned *sectors, unsigned max_segs,
 196                             unsigned max_sectors)
 197 {
 198         unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
 199         unsigned len = min(bv->bv_len, max_len);
 200         unsigned total_len = 0;
 201         unsigned seg_size = 0;
 202 
 203         while (len && *nsegs < max_segs) {
 204                 seg_size = get_max_segment_size(q, bv->bv_offset + total_len);
 205                 seg_size = min(seg_size, len);
 206 
 207                 (*nsegs)++;
 208                 total_len += seg_size;
 209                 len -= seg_size;
 210 
 211                 if ((bv->bv_offset + total_len) & queue_virt_boundary(q))
 212                         break;
 213         }
 214 
 215         *sectors += total_len >> 9;
 216 
 217         /* tell the caller to split the bvec if it is too big to fit */
 218         return len > 0 || bv->bv_len > max_len;
 219 }
 220 
 221 /**
 222  * blk_bio_segment_split - split a bio in two bios
 223  * @q:    [in] request queue pointer
 224  * @bio:  [in] bio to be split
 225  * @bs:   [in] bio set to allocate the clone from
 226  * @segs: [out] number of segments in the bio with the first half of the sectors
 227  *
 228  * Clone @bio, update the bi_iter of the clone to represent the first sectors
 229  * of @bio and update @bio->bi_iter to represent the remaining sectors. The
 230  * following is guaranteed for the cloned bio:
 231  * - That it has at most get_max_io_size(@q, @bio) sectors.
 232  * - That it has at most queue_max_segments(@q) segments.
 233  *
 234  * Except for discard requests the cloned bio will point at the bi_io_vec of
 235  * the original bio. It is the responsibility of the caller to ensure that the
 236  * original bio is not freed before the cloned bio. The caller is also
 237  * responsible for ensuring that @bs is only destroyed after processing of the
 238  * split bio has finished.
 239  */
 240 static struct bio *blk_bio_segment_split(struct request_queue *q,
 241                                          struct bio *bio,
 242                                          struct bio_set *bs,
 243                                          unsigned *segs)
 244 {
 245         struct bio_vec bv, bvprv, *bvprvp = NULL;
 246         struct bvec_iter iter;
 247         unsigned nsegs = 0, sectors = 0;
 248         const unsigned max_sectors = get_max_io_size(q, bio);
 249         const unsigned max_segs = queue_max_segments(q);
 250 
 251         bio_for_each_bvec(bv, bio, iter) {
 252                 /*
 253                  * If the queue doesn't support SG gaps and adding this
 254                  * offset would create a gap, disallow it.
 255                  */
 256                 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
 257                         goto split;
 258 
 259                 if (nsegs < max_segs &&
 260                     sectors + (bv.bv_len >> 9) <= max_sectors &&
 261                     bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
 262                         nsegs++;
 263                         sectors += bv.bv_len >> 9;
 264                 } else if (bvec_split_segs(q, &bv, &nsegs, &sectors, max_segs,
 265                                          max_sectors)) {
 266                         goto split;
 267                 }
 268 
 269                 bvprv = bv;
 270                 bvprvp = &bvprv;
 271         }
 272 
 273         *segs = nsegs;
 274         return NULL;
 275 split:
 276         *segs = nsegs;
 277         return bio_split(bio, sectors, GFP_NOIO, bs);
 278 }
 279 
 280 /**
 281  * __blk_queue_split - split a bio and submit the second half
 282  * @q:       [in] request queue pointer
 283  * @bio:     [in, out] bio to be split
 284  * @nr_segs: [out] number of segments in the first bio
 285  *
 286  * Split a bio into two bios, chain the two bios, submit the second half and
 287  * store a pointer to the first half in *@bio. If the second bio is still too
 288  * big it will be split by a recursive call to this function. Since this
 289  * function may allocate a new bio from @q->bio_split, it is the responsibility
 290  * of the caller to ensure that @q is only released after processing of the
 291  * split bio has finished.
 292  */
 293 void __blk_queue_split(struct request_queue *q, struct bio **bio,
 294                 unsigned int *nr_segs)
 295 {
 296         struct bio *split;
 297 
 298         switch (bio_op(*bio)) {
 299         case REQ_OP_DISCARD:
 300         case REQ_OP_SECURE_ERASE:
 301                 split = blk_bio_discard_split(q, *bio, &q->bio_split, nr_segs);
 302                 break;
 303         case REQ_OP_WRITE_ZEROES:
 304                 split = blk_bio_write_zeroes_split(q, *bio, &q->bio_split,
 305                                 nr_segs);
 306                 break;
 307         case REQ_OP_WRITE_SAME:
 308                 split = blk_bio_write_same_split(q, *bio, &q->bio_split,
 309                                 nr_segs);
 310                 break;
 311         default:
 312                 split = blk_bio_segment_split(q, *bio, &q->bio_split, nr_segs);
 313                 break;
 314         }
 315 
 316         if (split) {
 317                 /* there isn't chance to merge the splitted bio */
 318                 split->bi_opf |= REQ_NOMERGE;
 319 
 320                 /*
 321                  * Since we're recursing into make_request here, ensure
 322                  * that we mark this bio as already having entered the queue.
 323                  * If not, and the queue is going away, we can get stuck
 324                  * forever on waiting for the queue reference to drop. But
 325                  * that will never happen, as we're already holding a
 326                  * reference to it.
 327                  */
 328                 bio_set_flag(*bio, BIO_QUEUE_ENTERED);
 329 
 330                 bio_chain(split, *bio);
 331                 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
 332                 generic_make_request(*bio);
 333                 *bio = split;
 334         }
 335 }
 336 
 337 /**
 338  * blk_queue_split - split a bio and submit the second half
 339  * @q:   [in] request queue pointer
 340  * @bio: [in, out] bio to be split
 341  *
 342  * Split a bio into two bios, chains the two bios, submit the second half and
 343  * store a pointer to the first half in *@bio. Since this function may allocate
 344  * a new bio from @q->bio_split, it is the responsibility of the caller to
 345  * ensure that @q is only released after processing of the split bio has
 346  * finished.
 347  */
 348 void blk_queue_split(struct request_queue *q, struct bio **bio)
 349 {
 350         unsigned int nr_segs;
 351 
 352         __blk_queue_split(q, bio, &nr_segs);
 353 }
 354 EXPORT_SYMBOL(blk_queue_split);
 355 
 356 unsigned int blk_recalc_rq_segments(struct request *rq)
 357 {
 358         unsigned int nr_phys_segs = 0;
 359         unsigned int nr_sectors = 0;
 360         struct req_iterator iter;
 361         struct bio_vec bv;
 362 
 363         if (!rq->bio)
 364                 return 0;
 365 
 366         switch (bio_op(rq->bio)) {
 367         case REQ_OP_DISCARD:
 368         case REQ_OP_SECURE_ERASE:
 369         case REQ_OP_WRITE_ZEROES:
 370                 return 0;
 371         case REQ_OP_WRITE_SAME:
 372                 return 1;
 373         }
 374 
 375         rq_for_each_bvec(bv, rq, iter)
 376                 bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
 377                                 UINT_MAX, UINT_MAX);
 378         return nr_phys_segs;
 379 }
 380 
 381 static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
 382                 struct scatterlist *sglist)
 383 {
 384         if (!*sg)
 385                 return sglist;
 386 
 387         /*
 388          * If the driver previously mapped a shorter list, we could see a
 389          * termination bit prematurely unless it fully inits the sg table
 390          * on each mapping. We KNOW that there must be more entries here
 391          * or the driver would be buggy, so force clear the termination bit
 392          * to avoid doing a full sg_init_table() in drivers for each command.
 393          */
 394         sg_unmark_end(*sg);
 395         return sg_next(*sg);
 396 }
 397 
 398 static unsigned blk_bvec_map_sg(struct request_queue *q,
 399                 struct bio_vec *bvec, struct scatterlist *sglist,
 400                 struct scatterlist **sg)
 401 {
 402         unsigned nbytes = bvec->bv_len;
 403         unsigned nsegs = 0, total = 0;
 404 
 405         while (nbytes > 0) {
 406                 unsigned offset = bvec->bv_offset + total;
 407                 unsigned len = min(get_max_segment_size(q, offset), nbytes);
 408                 struct page *page = bvec->bv_page;
 409 
 410                 /*
 411                  * Unfortunately a fair number of drivers barf on scatterlists
 412                  * that have an offset larger than PAGE_SIZE, despite other
 413                  * subsystems dealing with that invariant just fine.  For now
 414                  * stick to the legacy format where we never present those from
 415                  * the block layer, but the code below should be removed once
 416                  * these offenders (mostly MMC/SD drivers) are fixed.
 417                  */
 418                 page += (offset >> PAGE_SHIFT);
 419                 offset &= ~PAGE_MASK;
 420 
 421                 *sg = blk_next_sg(sg, sglist);
 422                 sg_set_page(*sg, page, len, offset);
 423 
 424                 total += len;
 425                 nbytes -= len;
 426                 nsegs++;
 427         }
 428 
 429         return nsegs;
 430 }
 431 
 432 static inline int __blk_bvec_map_sg(struct bio_vec bv,
 433                 struct scatterlist *sglist, struct scatterlist **sg)
 434 {
 435         *sg = blk_next_sg(sg, sglist);
 436         sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
 437         return 1;
 438 }
 439 
 440 /* only try to merge bvecs into one sg if they are from two bios */
 441 static inline bool
 442 __blk_segment_map_sg_merge(struct request_queue *q, struct bio_vec *bvec,
 443                            struct bio_vec *bvprv, struct scatterlist **sg)
 444 {
 445 
 446         int nbytes = bvec->bv_len;
 447 
 448         if (!*sg)
 449                 return false;
 450 
 451         if ((*sg)->length + nbytes > queue_max_segment_size(q))
 452                 return false;
 453 
 454         if (!biovec_phys_mergeable(q, bvprv, bvec))
 455                 return false;
 456 
 457         (*sg)->length += nbytes;
 458 
 459         return true;
 460 }
 461 
 462 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 463                              struct scatterlist *sglist,
 464                              struct scatterlist **sg)
 465 {
 466         struct bio_vec uninitialized_var(bvec), bvprv = { NULL };
 467         struct bvec_iter iter;
 468         int nsegs = 0;
 469         bool new_bio = false;
 470 
 471         for_each_bio(bio) {
 472                 bio_for_each_bvec(bvec, bio, iter) {
 473                         /*
 474                          * Only try to merge bvecs from two bios given we
 475                          * have done bio internal merge when adding pages
 476                          * to bio
 477                          */
 478                         if (new_bio &&
 479                             __blk_segment_map_sg_merge(q, &bvec, &bvprv, sg))
 480                                 goto next_bvec;
 481 
 482                         if (bvec.bv_offset + bvec.bv_len <= PAGE_SIZE)
 483                                 nsegs += __blk_bvec_map_sg(bvec, sglist, sg);
 484                         else
 485                                 nsegs += blk_bvec_map_sg(q, &bvec, sglist, sg);
 486  next_bvec:
 487                         new_bio = false;
 488                 }
 489                 if (likely(bio->bi_iter.bi_size)) {
 490                         bvprv = bvec;
 491                         new_bio = true;
 492                 }
 493         }
 494 
 495         return nsegs;
 496 }
 497 
 498 /*
 499  * map a request to scatterlist, return number of sg entries setup. Caller
 500  * must make sure sg can hold rq->nr_phys_segments entries
 501  */
 502 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 503                   struct scatterlist *sglist)
 504 {
 505         struct scatterlist *sg = NULL;
 506         int nsegs = 0;
 507 
 508         if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
 509                 nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, &sg);
 510         else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
 511                 nsegs = __blk_bvec_map_sg(bio_iovec(rq->bio), sglist, &sg);
 512         else if (rq->bio)
 513                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 514 
 515         if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
 516             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 517                 unsigned int pad_len =
 518                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 519 
 520                 sg->length += pad_len;
 521                 rq->extra_len += pad_len;
 522         }
 523 
 524         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 525                 if (op_is_write(req_op(rq)))
 526                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 527 
 528                 sg_unmark_end(sg);
 529                 sg = sg_next(sg);
 530                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 531                             q->dma_drain_size,
 532                             ((unsigned long)q->dma_drain_buffer) &
 533                             (PAGE_SIZE - 1));
 534                 nsegs++;
 535                 rq->extra_len += q->dma_drain_size;
 536         }
 537 
 538         if (sg)
 539                 sg_mark_end(sg);
 540 
 541         /*
 542          * Something must have been wrong if the figured number of
 543          * segment is bigger than number of req's physical segments
 544          */
 545         WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
 546 
 547         return nsegs;
 548 }
 549 EXPORT_SYMBOL(blk_rq_map_sg);
 550 
 551 static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
 552                 unsigned int nr_phys_segs)
 553 {
 554         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(req->q))
 555                 goto no_merge;
 556 
 557         if (blk_integrity_merge_bio(req->q, req, bio) == false)
 558                 goto no_merge;
 559 
 560         /*
 561          * This will form the start of a new hw segment.  Bump both
 562          * counters.
 563          */
 564         req->nr_phys_segments += nr_phys_segs;
 565         return 1;
 566 
 567 no_merge:
 568         req_set_nomerge(req->q, req);
 569         return 0;
 570 }
 571 
 572 int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
 573 {
 574         if (req_gap_back_merge(req, bio))
 575                 return 0;
 576         if (blk_integrity_rq(req) &&
 577             integrity_req_gap_back_merge(req, bio))
 578                 return 0;
 579         if (blk_rq_sectors(req) + bio_sectors(bio) >
 580             blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
 581                 req_set_nomerge(req->q, req);
 582                 return 0;
 583         }
 584 
 585         return ll_new_hw_segment(req, bio, nr_segs);
 586 }
 587 
 588 int ll_front_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
 589 {
 590         if (req_gap_front_merge(req, bio))
 591                 return 0;
 592         if (blk_integrity_rq(req) &&
 593             integrity_req_gap_front_merge(req, bio))
 594                 return 0;
 595         if (blk_rq_sectors(req) + bio_sectors(bio) >
 596             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
 597                 req_set_nomerge(req->q, req);
 598                 return 0;
 599         }
 600 
 601         return ll_new_hw_segment(req, bio, nr_segs);
 602 }
 603 
 604 static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
 605                 struct request *next)
 606 {
 607         unsigned short segments = blk_rq_nr_discard_segments(req);
 608 
 609         if (segments >= queue_max_discard_segments(q))
 610                 goto no_merge;
 611         if (blk_rq_sectors(req) + bio_sectors(next->bio) >
 612             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 613                 goto no_merge;
 614 
 615         req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
 616         return true;
 617 no_merge:
 618         req_set_nomerge(q, req);
 619         return false;
 620 }
 621 
 622 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 623                                 struct request *next)
 624 {
 625         int total_phys_segments;
 626 
 627         if (req_gap_back_merge(req, next->bio))
 628                 return 0;
 629 
 630         /*
 631          * Will it become too large?
 632          */
 633         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 634             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 635                 return 0;
 636 
 637         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 638         if (total_phys_segments > queue_max_segments(q))
 639                 return 0;
 640 
 641         if (blk_integrity_merge_rq(q, req, next) == false)
 642                 return 0;
 643 
 644         /* Merge is OK... */
 645         req->nr_phys_segments = total_phys_segments;
 646         return 1;
 647 }
 648 
 649 /**
 650  * blk_rq_set_mixed_merge - mark a request as mixed merge
 651  * @rq: request to mark as mixed merge
 652  *
 653  * Description:
 654  *     @rq is about to be mixed merged.  Make sure the attributes
 655  *     which can be mixed are set in each bio and mark @rq as mixed
 656  *     merged.
 657  */
 658 void blk_rq_set_mixed_merge(struct request *rq)
 659 {
 660         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 661         struct bio *bio;
 662 
 663         if (rq->rq_flags & RQF_MIXED_MERGE)
 664                 return;
 665 
 666         /*
 667          * @rq will no longer represent mixable attributes for all the
 668          * contained bios.  It will just track those of the first one.
 669          * Distributes the attributs to each bio.
 670          */
 671         for (bio = rq->bio; bio; bio = bio->bi_next) {
 672                 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
 673                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
 674                 bio->bi_opf |= ff;
 675         }
 676         rq->rq_flags |= RQF_MIXED_MERGE;
 677 }
 678 
 679 static void blk_account_io_merge(struct request *req)
 680 {
 681         if (blk_do_io_stat(req)) {
 682                 struct hd_struct *part;
 683 
 684                 part_stat_lock();
 685                 part = req->part;
 686 
 687                 part_dec_in_flight(req->q, part, rq_data_dir(req));
 688 
 689                 hd_struct_put(part);
 690                 part_stat_unlock();
 691         }
 692 }
 693 /*
 694  * Two cases of handling DISCARD merge:
 695  * If max_discard_segments > 1, the driver takes every bio
 696  * as a range and send them to controller together. The ranges
 697  * needn't to be contiguous.
 698  * Otherwise, the bios/requests will be handled as same as
 699  * others which should be contiguous.
 700  */
 701 static inline bool blk_discard_mergable(struct request *req)
 702 {
 703         if (req_op(req) == REQ_OP_DISCARD &&
 704             queue_max_discard_segments(req->q) > 1)
 705                 return true;
 706         return false;
 707 }
 708 
 709 static enum elv_merge blk_try_req_merge(struct request *req,
 710                                         struct request *next)
 711 {
 712         if (blk_discard_mergable(req))
 713                 return ELEVATOR_DISCARD_MERGE;
 714         else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
 715                 return ELEVATOR_BACK_MERGE;
 716 
 717         return ELEVATOR_NO_MERGE;
 718 }
 719 
 720 /*
 721  * For non-mq, this has to be called with the request spinlock acquired.
 722  * For mq with scheduling, the appropriate queue wide lock should be held.
 723  */
 724 static struct request *attempt_merge(struct request_queue *q,
 725                                      struct request *req, struct request *next)
 726 {
 727         if (!rq_mergeable(req) || !rq_mergeable(next))
 728                 return NULL;
 729 
 730         if (req_op(req) != req_op(next))
 731                 return NULL;
 732 
 733         if (rq_data_dir(req) != rq_data_dir(next)
 734             || req->rq_disk != next->rq_disk)
 735                 return NULL;
 736 
 737         if (req_op(req) == REQ_OP_WRITE_SAME &&
 738             !blk_write_same_mergeable(req->bio, next->bio))
 739                 return NULL;
 740 
 741         /*
 742          * Don't allow merge of different write hints, or for a hint with
 743          * non-hint IO.
 744          */
 745         if (req->write_hint != next->write_hint)
 746                 return NULL;
 747 
 748         if (req->ioprio != next->ioprio)
 749                 return NULL;
 750 
 751         /*
 752          * If we are allowed to merge, then append bio list
 753          * from next to rq and release next. merge_requests_fn
 754          * will have updated segment counts, update sector
 755          * counts here. Handle DISCARDs separately, as they
 756          * have separate settings.
 757          */
 758 
 759         switch (blk_try_req_merge(req, next)) {
 760         case ELEVATOR_DISCARD_MERGE:
 761                 if (!req_attempt_discard_merge(q, req, next))
 762                         return NULL;
 763                 break;
 764         case ELEVATOR_BACK_MERGE:
 765                 if (!ll_merge_requests_fn(q, req, next))
 766                         return NULL;
 767                 break;
 768         default:
 769                 return NULL;
 770         }
 771 
 772         /*
 773          * If failfast settings disagree or any of the two is already
 774          * a mixed merge, mark both as mixed before proceeding.  This
 775          * makes sure that all involved bios have mixable attributes
 776          * set properly.
 777          */
 778         if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
 779             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 780             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 781                 blk_rq_set_mixed_merge(req);
 782                 blk_rq_set_mixed_merge(next);
 783         }
 784 
 785         /*
 786          * At this point we have either done a back merge or front merge. We
 787          * need the smaller start_time_ns of the merged requests to be the
 788          * current request for accounting purposes.
 789          */
 790         if (next->start_time_ns < req->start_time_ns)
 791                 req->start_time_ns = next->start_time_ns;
 792 
 793         req->biotail->bi_next = next->bio;
 794         req->biotail = next->biotail;
 795 
 796         req->__data_len += blk_rq_bytes(next);
 797 
 798         if (!blk_discard_mergable(req))
 799                 elv_merge_requests(q, req, next);
 800 
 801         /*
 802          * 'next' is going away, so update stats accordingly
 803          */
 804         blk_account_io_merge(next);
 805 
 806         /*
 807          * ownership of bio passed from next to req, return 'next' for
 808          * the caller to free
 809          */
 810         next->bio = NULL;
 811         return next;
 812 }
 813 
 814 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
 815 {
 816         struct request *next = elv_latter_request(q, rq);
 817 
 818         if (next)
 819                 return attempt_merge(q, rq, next);
 820 
 821         return NULL;
 822 }
 823 
 824 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
 825 {
 826         struct request *prev = elv_former_request(q, rq);
 827 
 828         if (prev)
 829                 return attempt_merge(q, prev, rq);
 830 
 831         return NULL;
 832 }
 833 
 834 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 835                           struct request *next)
 836 {
 837         struct request *free;
 838 
 839         free = attempt_merge(q, rq, next);
 840         if (free) {
 841                 blk_put_request(free);
 842                 return 1;
 843         }
 844 
 845         return 0;
 846 }
 847 
 848 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 849 {
 850         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 851                 return false;
 852 
 853         if (req_op(rq) != bio_op(bio))
 854                 return false;
 855 
 856         /* different data direction or already started, don't merge */
 857         if (bio_data_dir(bio) != rq_data_dir(rq))
 858                 return false;
 859 
 860         /* must be same device */
 861         if (rq->rq_disk != bio->bi_disk)
 862                 return false;
 863 
 864         /* only merge integrity protected bio into ditto rq */
 865         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 866                 return false;
 867 
 868         /* must be using the same buffer */
 869         if (req_op(rq) == REQ_OP_WRITE_SAME &&
 870             !blk_write_same_mergeable(rq->bio, bio))
 871                 return false;
 872 
 873         /*
 874          * Don't allow merge of different write hints, or for a hint with
 875          * non-hint IO.
 876          */
 877         if (rq->write_hint != bio->bi_write_hint)
 878                 return false;
 879 
 880         if (rq->ioprio != bio_prio(bio))
 881                 return false;
 882 
 883         return true;
 884 }
 885 
 886 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 887 {
 888         if (blk_discard_mergable(rq))
 889                 return ELEVATOR_DISCARD_MERGE;
 890         else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 891                 return ELEVATOR_BACK_MERGE;
 892         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 893                 return ELEVATOR_FRONT_MERGE;
 894         return ELEVATOR_NO_MERGE;
 895 }
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root/block/blk-merge.c

DEFINITIONS
