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