linux/block/blk-merge.c
<<
>>
Prefs
   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        unsigned short max_sectors;
 279
 280        if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
 281                max_sectors = queue_max_hw_sectors(q);
 282        else
 283                max_sectors = queue_max_sectors(q);
 284
 285        if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
 286                req->cmd_flags |= REQ_NOMERGE;
 287                if (req == q->last_merge)
 288                        q->last_merge = NULL;
 289                return 0;
 290        }
 291        if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 292                blk_recount_segments(q, req->biotail);
 293        if (!bio_flagged(bio, BIO_SEG_VALID))
 294                blk_recount_segments(q, bio);
 295
 296        return ll_new_hw_segment(q, req, bio);
 297}
 298
 299int ll_front_merge_fn(struct request_queue *q, struct request *req,
 300                      struct bio *bio)
 301{
 302        unsigned short max_sectors;
 303
 304        if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
 305                max_sectors = queue_max_hw_sectors(q);
 306        else
 307                max_sectors = queue_max_sectors(q);
 308
 309
 310        if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
 311                req->cmd_flags |= REQ_NOMERGE;
 312                if (req == q->last_merge)
 313                        q->last_merge = NULL;
 314                return 0;
 315        }
 316        if (!bio_flagged(bio, BIO_SEG_VALID))
 317                blk_recount_segments(q, bio);
 318        if (!bio_flagged(req->bio, BIO_SEG_VALID))
 319                blk_recount_segments(q, req->bio);
 320
 321        return ll_new_hw_segment(q, req, bio);
 322}
 323
 324static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 325                                struct request *next)
 326{
 327        int total_phys_segments;
 328        unsigned int seg_size =
 329                req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 330
 331        /*
 332         * First check if the either of the requests are re-queued
 333         * requests.  Can't merge them if they are.
 334         */
 335        if (req->special || next->special)
 336                return 0;
 337
 338        /*
 339         * Will it become too large?
 340         */
 341        if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q))
 342                return 0;
 343
 344        total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 345        if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 346                if (req->nr_phys_segments == 1)
 347                        req->bio->bi_seg_front_size = seg_size;
 348                if (next->nr_phys_segments == 1)
 349                        next->biotail->bi_seg_back_size = seg_size;
 350                total_phys_segments--;
 351        }
 352
 353        if (total_phys_segments > queue_max_segments(q))
 354                return 0;
 355
 356        if (blk_integrity_rq(req) && blk_integrity_merge_rq(q, req, next))
 357                return 0;
 358
 359        /* Merge is OK... */
 360        req->nr_phys_segments = total_phys_segments;
 361        return 1;
 362}
 363
 364/**
 365 * blk_rq_set_mixed_merge - mark a request as mixed merge
 366 * @rq: request to mark as mixed merge
 367 *
 368 * Description:
 369 *     @rq is about to be mixed merged.  Make sure the attributes
 370 *     which can be mixed are set in each bio and mark @rq as mixed
 371 *     merged.
 372 */
 373void blk_rq_set_mixed_merge(struct request *rq)
 374{
 375        unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 376        struct bio *bio;
 377
 378        if (rq->cmd_flags & REQ_MIXED_MERGE)
 379                return;
 380
 381        /*
 382         * @rq will no longer represent mixable attributes for all the
 383         * contained bios.  It will just track those of the first one.
 384         * Distributes the attributs to each bio.
 385         */
 386        for (bio = rq->bio; bio; bio = bio->bi_next) {
 387                WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
 388                             (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
 389                bio->bi_rw |= ff;
 390        }
 391        rq->cmd_flags |= REQ_MIXED_MERGE;
 392}
 393
 394static void blk_account_io_merge(struct request *req)
 395{
 396        if (blk_do_io_stat(req)) {
 397                struct hd_struct *part;
 398                int cpu;
 399
 400                cpu = part_stat_lock();
 401                part = req->part;
 402
 403                part_round_stats(cpu, part);
 404                part_dec_in_flight(part, rq_data_dir(req));
 405
 406                hd_struct_put(part);
 407                part_stat_unlock();
 408        }
 409}
 410
 411/*
 412 * Has to be called with the request spinlock acquired
 413 */
 414static int attempt_merge(struct request_queue *q, struct request *req,
 415                          struct request *next)
 416{
 417        if (!rq_mergeable(req) || !rq_mergeable(next))
 418                return 0;
 419
 420        /*
 421         * Don't merge file system requests and discard requests
 422         */
 423        if ((req->cmd_flags & REQ_DISCARD) != (next->cmd_flags & REQ_DISCARD))
 424                return 0;
 425
 426        /*
 427         * Don't merge discard requests and secure discard requests
 428         */
 429        if ((req->cmd_flags & REQ_SECURE) != (next->cmd_flags & REQ_SECURE))
 430                return 0;
 431
 432        /*
 433         * not contiguous
 434         */
 435        if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 436                return 0;
 437
 438        if (rq_data_dir(req) != rq_data_dir(next)
 439            || req->rq_disk != next->rq_disk
 440            || next->special)
 441                return 0;
 442
 443        /*
 444         * If we are allowed to merge, then append bio list
 445         * from next to rq and release next. merge_requests_fn
 446         * will have updated segment counts, update sector
 447         * counts here.
 448         */
 449        if (!ll_merge_requests_fn(q, req, next))
 450                return 0;
 451
 452        /*
 453         * If failfast settings disagree or any of the two is already
 454         * a mixed merge, mark both as mixed before proceeding.  This
 455         * makes sure that all involved bios have mixable attributes
 456         * set properly.
 457         */
 458        if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
 459            (req->cmd_flags & REQ_FAILFAST_MASK) !=
 460            (next->cmd_flags & REQ_FAILFAST_MASK)) {
 461                blk_rq_set_mixed_merge(req);
 462                blk_rq_set_mixed_merge(next);
 463        }
 464
 465        /*
 466         * At this point we have either done a back merge
 467         * or front merge. We need the smaller start_time of
 468         * the merged requests to be the current request
 469         * for accounting purposes.
 470         */
 471        if (time_after(req->start_time, next->start_time))
 472                req->start_time = next->start_time;
 473
 474        req->biotail->bi_next = next->bio;
 475        req->biotail = next->biotail;
 476
 477        req->__data_len += blk_rq_bytes(next);
 478
 479        elv_merge_requests(q, req, next);
 480
 481        /*
 482         * 'next' is going away, so update stats accordingly
 483         */
 484        blk_account_io_merge(next);
 485
 486        req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 487        if (blk_rq_cpu_valid(next))
 488                req->cpu = next->cpu;
 489
 490        /* owner-ship of bio passed from next to req */
 491        next->bio = NULL;
 492        __blk_put_request(q, next);
 493        return 1;
 494}
 495
 496int attempt_back_merge(struct request_queue *q, struct request *rq)
 497{
 498        struct request *next = elv_latter_request(q, rq);
 499
 500        if (next)
 501                return attempt_merge(q, rq, next);
 502
 503        return 0;
 504}
 505
 506int attempt_front_merge(struct request_queue *q, struct request *rq)
 507{
 508        struct request *prev = elv_former_request(q, rq);
 509
 510        if (prev)
 511                return attempt_merge(q, prev, rq);
 512
 513        return 0;
 514}
 515
 516int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 517                          struct request *next)
 518{
 519        return attempt_merge(q, rq, next);
 520}
 521
 522bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 523{
 524        if (!rq_mergeable(rq))
 525                return false;
 526
 527        /* don't merge file system requests and discard requests */
 528        if ((bio->bi_rw & REQ_DISCARD) != (rq->bio->bi_rw & REQ_DISCARD))
 529                return false;
 530
 531        /* don't merge discard requests and secure discard requests */
 532        if ((bio->bi_rw & REQ_SECURE) != (rq->bio->bi_rw & REQ_SECURE))
 533                return false;
 534
 535        /* different data direction or already started, don't merge */
 536        if (bio_data_dir(bio) != rq_data_dir(rq))
 537                return false;
 538
 539        /* must be same device and not a special request */
 540        if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
 541                return false;
 542
 543        /* only merge integrity protected bio into ditto rq */
 544        if (bio_integrity(bio) != blk_integrity_rq(rq))
 545                return false;
 546
 547        return true;
 548}
 549
 550int blk_try_merge(struct request *rq, struct bio *bio)
 551{
 552        if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_sector)
 553                return ELEVATOR_BACK_MERGE;
 554        else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_sector)
 555                return ELEVATOR_FRONT_MERGE;
 556        return ELEVATOR_NO_MERGE;
 557}
 558
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.