block/blk-merge.c

   1 /*
   2  * Functions related to segment and merge handling
   3  */
   4 #include <linux/kernel.h>
   5 #include <linux/module.h>
   6 #include <linux/bio.h>
   7 #include <linux/blkdev.h>
   8 #include <linux/scatterlist.h>
   9
  10 #include "blk.h"
  11
  12 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
  13                                              struct bio *bio)
  14 {
  15         struct bio_vec bv, bvprv = { NULL };
  16         int cluster, high, highprv = 1, no_sg_merge;
  17         unsigned int seg_size, nr_phys_segs;
  18         struct bio *fbio, *bbio;
  19         struct bvec_iter iter;
  20
  21         if (!bio)
  22                 return 0;
  23
  24         /*
  25          * This should probably be returning 0, but blk_add_request_payload()
  26          * (Christoph!!!!)
  27          */
  28         if (bio->bi_rw & REQ_DISCARD)
  29                 return 1;
  30
  31         if (bio->bi_rw & REQ_WRITE_SAME)
  32                 return 1;
  33
  34         fbio = bio;
  35         cluster = blk_queue_cluster(q);
  36         seg_size = 0;
  37         nr_phys_segs = 0;
  38         no_sg_merge = test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags);
  39         high = 0;
  40         for_each_bio(bio) {
  41                 bio_for_each_segment(bv, bio, iter) {
  42                         /*
  43                          * If SG merging is disabled, each bio vector is
  44                          * a segment
  45                          */
  46                         if (no_sg_merge)
  47                                 goto new_segment;
  48
  49                         /*
  50                          * the trick here is making sure that a high page is
  51                          * never considered part of another segment, since
  52                          * that might change with the bounce page.
  53                          */
  54                         high = page_to_pfn(bv.bv_page) > queue_bounce_pfn(q);
  55                         if (!high && !highprv && cluster) {
  56                                 if (seg_size + bv.bv_len
  57                                     > queue_max_segment_size(q))
  58                                         goto new_segment;
  59                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
  60                                         goto new_segment;
  61                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
  62                                         goto new_segment;
  63
  64                                 seg_size += bv.bv_len;
  65                                 bvprv = bv;
  66                                 continue;
  67                         }
  68 new_segment:
  69                         if (nr_phys_segs == 1 && seg_size >
  70                             fbio->bi_seg_front_size)
  71                                 fbio->bi_seg_front_size = seg_size;
  72
  73                         nr_phys_segs++;
  74                         bvprv = bv;
  75                         seg_size = bv.bv_len;
  76                         highprv = high;
  77                 }
  78                 bbio = bio;
  79         }
  80
  81         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
  82                 fbio->bi_seg_front_size = seg_size;
  83         if (seg_size > bbio->bi_seg_back_size)
  84                 bbio->bi_seg_back_size = seg_size;
  85
  86         return nr_phys_segs;
  87 }
  88
  89 void blk_recalc_rq_segments(struct request *rq)
  90 {
  91         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
  92 }
  93
  94 void blk_recount_segments(struct request_queue *q, struct bio *bio)
  95 {
  96         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags))
  97                 bio->bi_phys_segments = bio->bi_vcnt;
  98         else {
  99                 struct bio *nxt = bio->bi_next;
 100
 101                 bio->bi_next = NULL;
 102                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
 103                 bio->bi_next = nxt;
 104         }
 105
 106         bio->bi_flags |= (1 << BIO_SEG_VALID);
 107 }
 108 EXPORT_SYMBOL(blk_recount_segments);
 109
 110 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 111                                    struct bio *nxt)
 112 {
 113         struct bio_vec end_bv = { NULL }, nxt_bv;
 114         struct bvec_iter iter;
 115
 116         if (!blk_queue_cluster(q))
 117                 return 0;
 118
 119         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 120             queue_max_segment_size(q))
 121                 return 0;
 122
 123         if (!bio_has_data(bio))
 124                 return 1;
 125
 126         bio_for_each_segment(end_bv, bio, iter)
 127                 if (end_bv.bv_len == iter.bi_size)
 128                         break;
 129
 130         nxt_bv = bio_iovec(nxt);
 131
 132         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 133                 return 0;
 134
 135         /*
 136          * bio and nxt are contiguous in memory; check if the queue allows
 137          * these two to be merged into one
 138          */
 139         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 140                 return 1;
 141
 142         return 0;
 143 }
 144
 145 static inline void
 146 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 147                      struct scatterlist *sglist, struct bio_vec *bvprv,
 148                      struct scatterlist **sg, int *nsegs, int *cluster)
 149 {
 150
 151         int nbytes = bvec->bv_len;
 152
 153         if (*sg && *cluster) {
 154                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 155                         goto new_segment;
 156
 157                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 158                         goto new_segment;
 159                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 160                         goto new_segment;
 161
 162                 (*sg)->length += nbytes;
 163         } else {
 164 new_segment:
 165                 if (!*sg)
 166                         *sg = sglist;
 167                 else {
 168                         /*
 169                          * If the driver previously mapped a shorter
 170                          * list, we could see a termination bit
 171                          * prematurely unless it fully inits the sg
 172                          * table on each mapping. We KNOW that there
 173                          * must be more entries here or the driver
 174                          * would be buggy, so force clear the
 175                          * termination bit to avoid doing a full
 176                          * sg_init_table() in drivers for each command.
 177                          */
 178                         sg_unmark_end(*sg);
 179                         *sg = sg_next(*sg);
 180                 }
 181
 182                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 183                 (*nsegs)++;
 184         }
 185         *bvprv = *bvec;
 186 }
 187
 188 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 189                              struct scatterlist *sglist,
 190                              struct scatterlist **sg)
 191 {
 192         struct bio_vec bvec, bvprv = { NULL };
 193         struct bvec_iter iter;
 194         int nsegs, cluster;
 195
 196         nsegs = 0;
 197         cluster = blk_queue_cluster(q);
 198
 199         if (bio->bi_rw & REQ_DISCARD) {
 200                 /*
 201                  * This is a hack - drivers should be neither modifying the
 202                  * biovec, nor relying on bi_vcnt - but because of
 203                  * blk_add_request_payload(), a discard bio may or may not have
 204                  * a payload we need to set up here (thank you Christoph) and
 205                  * bi_vcnt is really the only way of telling if we need to.
 206                  */
 207
 208                 if (bio->bi_vcnt)
 209                         goto single_segment;
 210
 211                 return 0;
 212         }
 213
 214         if (bio->bi_rw & REQ_WRITE_SAME) {
 215 single_segment:
 216                 *sg = sglist;
 217                 bvec = bio_iovec(bio);
 218                 sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
 219                 return 1;
 220         }
 221
 222         for_each_bio(bio)
 223                 bio_for_each_segment(bvec, bio, iter)
 224                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 225                                              &nsegs, &cluster);
 226
 227         return nsegs;
 228 }
 229
 230 /*
 231  * map a request to scatterlist, return number of sg entries setup. Caller
 232  * must make sure sg can hold rq->nr_phys_segments entries
 233  */
 234 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 235                   struct scatterlist *sglist)
 236 {
 237         struct scatterlist *sg = NULL;
 238         int nsegs = 0;
 239
 240         if (rq->bio)
 241                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 242
 243         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 244             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 245                 unsigned int pad_len =
 246                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 247
 248                 sg->length += pad_len;
 249                 rq->extra_len += pad_len;
 250         }
 251
 252         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 253                 if (rq->cmd_flags & REQ_WRITE)
 254                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 255
 256                 sg->page_link &= ~0x02;
 257                 sg = sg_next(sg);
 258                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 259                             q->dma_drain_size,
 260                             ((unsigned long)q->dma_drain_buffer) &
 261                             (PAGE_SIZE - 1));
 262                 nsegs++;
 263                 rq->extra_len += q->dma_drain_size;
 264         }
 265
 266         if (sg)
 267                 sg_mark_end(sg);
 268
 269         return nsegs;
 270 }
 271 EXPORT_SYMBOL(blk_rq_map_sg);
 272
 273 /**
 274  * blk_bio_map_sg - map a bio to a scatterlist
 275  * @q: request_queue in question
 276  * @bio: bio being mapped
 277  * @sglist: scatterlist being mapped
 278  *
 279  * Note:
 280  *    Caller must make sure sg can hold bio->bi_phys_segments entries
 281  *
 282  * Will return the number of sg entries setup
 283  */
 284 int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
 285                    struct scatterlist *sglist)
 286 {
 287         struct scatterlist *sg = NULL;
 288         int nsegs;
 289         struct bio *next = bio->bi_next;
 290         bio->bi_next = NULL;
 291
 292         nsegs = __blk_bios_map_sg(q, bio, sglist, &sg);
 293         bio->bi_next = next;
 294         if (sg)
 295                 sg_mark_end(sg);
 296
 297         BUG_ON(bio->bi_phys_segments && nsegs > bio->bi_phys_segments);
 298         return nsegs;
 299 }
 300 EXPORT_SYMBOL(blk_bio_map_sg);
 301
 302 static inline int ll_new_hw_segment(struct request_queue *q,
 303                                     struct request *req,
 304                                     struct bio *bio)
 305 {
 306         int nr_phys_segs = bio_phys_segments(q, bio);
 307
 308         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 309                 goto no_merge;
 310
 311         if (bio_integrity(bio) && blk_integrity_merge_bio(q, req, bio))
 312                 goto no_merge;
 313
 314         /*
 315          * This will form the start of a new hw segment.  Bump both
 316          * counters.
 317          */
 318         req->nr_phys_segments += nr_phys_segs;
 319         return 1;
 320
 321 no_merge:
 322         req->cmd_flags |= REQ_NOMERGE;
 323         if (req == q->last_merge)
 324                 q->last_merge = NULL;
 325         return 0;
 326 }
 327
 328 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 329                      struct bio *bio)
 330 {
 331         if (blk_rq_sectors(req) + bio_sectors(bio) >
 332             blk_rq_get_max_sectors(req)) {
 333                 req->cmd_flags |= REQ_NOMERGE;
 334                 if (req == q->last_merge)
 335                         q->last_merge = NULL;
 336                 return 0;
 337         }
 338         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 339                 blk_recount_segments(q, req->biotail);
 340         if (!bio_flagged(bio, BIO_SEG_VALID))
 341                 blk_recount_segments(q, bio);
 342
 343         return ll_new_hw_segment(q, req, bio);
 344 }
 345
 346 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 347                       struct bio *bio)
 348 {
 349         if (blk_rq_sectors(req) + bio_sectors(bio) >
 350             blk_rq_get_max_sectors(req)) {
 351                 req->cmd_flags |= REQ_NOMERGE;
 352                 if (req == q->last_merge)
 353                         q->last_merge = NULL;
 354                 return 0;
 355         }
 356         if (!bio_flagged(bio, BIO_SEG_VALID))
 357                 blk_recount_segments(q, bio);
 358         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 359                 blk_recount_segments(q, req->bio);
 360
 361         return ll_new_hw_segment(q, req, bio);
 362 }
 363
 364 /*
 365  * blk-mq uses req->special to carry normal driver per-request payload, it
 366  * does not indicate a prepared command that we cannot merge with.
 367  */
 368 static bool req_no_special_merge(struct request *req)
 369 {
 370         struct request_queue *q = req->q;
 371
 372         return !q->mq_ops && req->special;
 373 }
 374
 375 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 376                                 struct request *next)
 377 {
 378         int total_phys_segments;
 379         unsigned int seg_size =
 380                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 381
 382         /*
 383          * First check if the either of the requests are re-queued
 384          * requests.  Can't merge them if they are.
 385          */
 386         if (req_no_special_merge(req) || req_no_special_merge(next))
 387                 return 0;
 388
 389         /*
 390          * Will it become too large?
 391          */
 392         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 393             blk_rq_get_max_sectors(req))
 394                 return 0;
 395
 396         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 397         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 398                 if (req->nr_phys_segments == 1)
 399                         req->bio->bi_seg_front_size = seg_size;
 400                 if (next->nr_phys_segments == 1)
 401                         next->biotail->bi_seg_back_size = seg_size;
 402                 total_phys_segments--;
 403         }
 404
 405         if (total_phys_segments > queue_max_segments(q))
 406                 return 0;
 407
 408         if (blk_integrity_rq(req) && blk_integrity_merge_rq(q, req, next))
 409                 return 0;
 410
 411         /* Merge is OK... */
 412         req->nr_phys_segments = total_phys_segments;
 413         return 1;
 414 }
 415
 416 /**
 417  * blk_rq_set_mixed_merge - mark a request as mixed merge
 418  * @rq: request to mark as mixed merge
 419  *
 420  * Description:
 421  *     @rq is about to be mixed merged.  Make sure the attributes
 422  *     which can be mixed are set in each bio and mark @rq as mixed
 423  *     merged.
 424  */
 425 void blk_rq_set_mixed_merge(struct request *rq)
 426 {
 427         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 428         struct bio *bio;
 429
 430         if (rq->cmd_flags & REQ_MIXED_MERGE)
 431                 return;
 432
 433         /*
 434          * @rq will no longer represent mixable attributes for all the
 435          * contained bios.  It will just track those of the first one.
 436          * Distributes the attributs to each bio.
 437          */
 438         for (bio = rq->bio; bio; bio = bio->bi_next) {
 439                 WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
 440                              (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
 441                 bio->bi_rw |= ff;
 442         }
 443         rq->cmd_flags |= REQ_MIXED_MERGE;
 444 }
 445
 446 static void blk_account_io_merge(struct request *req)
 447 {
 448         if (blk_do_io_stat(req)) {
 449                 struct hd_struct *part;
 450                 int cpu;
 451
 452                 cpu = part_stat_lock();
 453                 part = req->part;
 454
 455                 part_round_stats(cpu, part);
 456                 part_dec_in_flight(part, rq_data_dir(req));
 457
 458                 hd_struct_put(part);
 459                 part_stat_unlock();
 460         }
 461 }
 462
 463 /*
 464  * Has to be called with the request spinlock acquired
 465  */
 466 static int attempt_merge(struct request_queue *q, struct request *req,
 467                           struct request *next)
 468 {
 469         if (!rq_mergeable(req) || !rq_mergeable(next))
 470                 return 0;
 471
 472         if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
 473                 return 0;
 474
 475         /*
 476          * not contiguous
 477          */
 478         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 479                 return 0;
 480
 481         if (rq_data_dir(req) != rq_data_dir(next)
 482             || req->rq_disk != next->rq_disk
 483             || req_no_special_merge(next))
 484                 return 0;
 485
 486         if (req->cmd_flags & REQ_WRITE_SAME &&
 487             !blk_write_same_mergeable(req->bio, next->bio))
 488                 return 0;
 489
 490         /*
 491          * If we are allowed to merge, then append bio list
 492          * from next to rq and release next. merge_requests_fn
 493          * will have updated segment counts, update sector
 494          * counts here.
 495          */
 496         if (!ll_merge_requests_fn(q, req, next))
 497                 return 0;
 498
 499         /*
 500          * If failfast settings disagree or any of the two is already
 501          * a mixed merge, mark both as mixed before proceeding.  This
 502          * makes sure that all involved bios have mixable attributes
 503          * set properly.
 504          */
 505         if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
 506             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 507             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 508                 blk_rq_set_mixed_merge(req);
 509                 blk_rq_set_mixed_merge(next);
 510         }
 511
 512         /*
 513          * At this point we have either done a back merge
 514          * or front merge. We need the smaller start_time of
 515          * the merged requests to be the current request
 516          * for accounting purposes.
 517          */
 518         if (time_after(req->start_time, next->start_time))
 519                 req->start_time = next->start_time;
 520
 521         req->biotail->bi_next = next->bio;
 522         req->biotail = next->biotail;
 523
 524         req->__data_len += blk_rq_bytes(next);
 525
 526         elv_merge_requests(q, req, next);
 527
 528         /*
 529          * 'next' is going away, so update stats accordingly
 530          */
 531         blk_account_io_merge(next);
 532
 533         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 534         if (blk_rq_cpu_valid(next))
 535                 req->cpu = next->cpu;
 536
 537         /* owner-ship of bio passed from next to req */
 538         next->bio = NULL;
 539         __blk_put_request(q, next);
 540         return 1;
 541 }
 542
 543 int attempt_back_merge(struct request_queue *q, struct request *rq)
 544 {
 545         struct request *next = elv_latter_request(q, rq);
 546
 547         if (next)
 548                 return attempt_merge(q, rq, next);
 549
 550         return 0;
 551 }
 552
 553 int attempt_front_merge(struct request_queue *q, struct request *rq)
 554 {
 555         struct request *prev = elv_former_request(q, rq);
 556
 557         if (prev)
 558                 return attempt_merge(q, prev, rq);
 559
 560         return 0;
 561 }
 562
 563 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 564                           struct request *next)
 565 {
 566         return attempt_merge(q, rq, next);
 567 }
 568
 569 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 570 {
 571         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 572                 return false;
 573
 574         if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
 575                 return false;
 576
 577         /* different data direction or already started, don't merge */
 578         if (bio_data_dir(bio) != rq_data_dir(rq))
 579                 return false;
 580
 581         /* must be same device and not a special request */
 582         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
 583                 return false;
 584
 585         /* only merge integrity protected bio into ditto rq */
 586         if (bio_integrity(bio) != blk_integrity_rq(rq))
 587                 return false;
 588
 589         /* must be using the same buffer */
 590         if (rq->cmd_flags & REQ_WRITE_SAME &&
 591             !blk_write_same_mergeable(rq->bio, bio))
 592                 return false;
 593
 594         return true;
 595 }
 596
 597 int blk_try_merge(struct request *rq, struct bio *bio)
 598 {
 599         if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 600                 return ELEVATOR_BACK_MERGE;
 601         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 602                 return ELEVATOR_FRONT_MERGE;
 603         return ELEVATOR_NO_MERGE;
 604 }