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
  12void blk_recalc_rq_sectors(struct request *rq, int nsect)
  13{
  14        if (blk_fs_request(rq) || blk_discard_rq(rq)) {
  15                rq->hard_sector += nsect;
  16                rq->hard_nr_sectors -= nsect;
  17
  18                /*
  19                 * Move the I/O submission pointers ahead if required.
  20                 */
  21                if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
  22                    (rq->sector <= rq->hard_sector)) {
  23                        rq->sector = rq->hard_sector;
  24                        rq->nr_sectors = rq->hard_nr_sectors;
  25                        rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
  26                        rq->current_nr_sectors = rq->hard_cur_sectors;
  27                        rq->buffer = bio_data(rq->bio);
  28                }
  29
  30                /*
  31                 * if total number of sectors is less than the first segment
  32                 * size, something has gone terribly wrong
  33                 */
  34                if (rq->nr_sectors < rq->current_nr_sectors) {
  35                        printk(KERN_ERR "blk: request botched\n");
  36                        rq->nr_sectors = rq->current_nr_sectors;
  37                }
  38        }
  39}
  40
  41static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
  42                                             struct bio *bio)
  43{
  44        unsigned int phys_size;
  45        struct bio_vec *bv, *bvprv = NULL;
  46        int cluster, i, high, highprv = 1;
  47        unsigned int seg_size, nr_phys_segs;
  48        struct bio *fbio, *bbio;
  49
  50        if (!bio)
  51                return 0;
  52
  53        fbio = bio;
  54        cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
  55        seg_size = 0;
  56        phys_size = nr_phys_segs = 0;
  57        for_each_bio(bio) {
  58                bio_for_each_segment(bv, bio, i) {
  59                        /*
  60                         * the trick here is making sure that a high page is
  61                         * never considered part of another segment, since that
  62                         * might change with the bounce page.
  63                         */
  64                        high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
  65                        if (high || highprv)
  66                                goto new_segment;
  67                        if (cluster) {
  68                                if (seg_size + bv->bv_len > q->max_segment_size)
  69                                        goto new_segment;
  70                                if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
  71                                        goto new_segment;
  72                                if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
  73                                        goto new_segment;
  74
  75                                seg_size += bv->bv_len;
  76                                bvprv = bv;
  77                                continue;
  78                        }
  79new_segment:
  80                        if (nr_phys_segs == 1 && seg_size >
  81                            fbio->bi_seg_front_size)
  82                                fbio->bi_seg_front_size = seg_size;
  83
  84                        nr_phys_segs++;
  85                        bvprv = bv;
  86                        seg_size = bv->bv_len;
  87                        highprv = high;
  88                }
  89                bbio = bio;
  90        }
  91
  92        if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
  93                fbio->bi_seg_front_size = seg_size;
  94        if (seg_size > bbio->bi_seg_back_size)
  95                bbio->bi_seg_back_size = seg_size;
  96
  97        return nr_phys_segs;
  98}
  99
 100void blk_recalc_rq_segments(struct request *rq)
 101{
 102        rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
 103}
 104
 105void blk_recount_segments(struct request_queue *q, struct bio *bio)
 106{
 107        struct bio *nxt = bio->bi_next;
 108
 109        bio->bi_next = NULL;
 110        bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
 111        bio->bi_next = nxt;
 112        bio->bi_flags |= (1 << BIO_SEG_VALID);
 113}
 114EXPORT_SYMBOL(blk_recount_segments);
 115
 116static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 117                                   struct bio *nxt)
 118{
 119        if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
 120                return 0;
 121
 122        if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 123            q->max_segment_size)
 124                return 0;
 125
 126        if (!bio_has_data(bio))
 127                return 1;
 128
 129        if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
 130                return 0;
 131
 132        /*
 133         * bio and nxt are contiguous in memory; check if the queue allows
 134         * these two to be merged into one
 135         */
 136        if (BIO_SEG_BOUNDARY(q, bio, nxt))
 137                return 1;
 138
 139        return 0;
 140}
 141
 142/*
 143 * map a request to scatterlist, return number of sg entries setup. Caller
 144 * must make sure sg can hold rq->nr_phys_segments entries
 145 */
 146int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 147                  struct scatterlist *sglist)
 148{
 149        struct bio_vec *bvec, *bvprv;
 150        struct req_iterator iter;
 151        struct scatterlist *sg;
 152        int nsegs, cluster;
 153
 154        nsegs = 0;
 155        cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
 156
 157        /*
 158         * for each bio in rq
 159         */
 160        bvprv = NULL;
 161        sg = NULL;
 162        rq_for_each_segment(bvec, rq, iter) {
 163                int nbytes = bvec->bv_len;
 164
 165                if (bvprv && cluster) {
 166                        if (sg->length + nbytes > q->max_segment_size)
 167                                goto new_segment;
 168
 169                        if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 170                                goto new_segment;
 171                        if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 172                                goto new_segment;
 173
 174                        sg->length += nbytes;
 175                } else {
 176new_segment:
 177                        if (!sg)
 178                                sg = sglist;
 179                        else {
 180                                /*
 181                                 * If the driver previously mapped a shorter
 182                                 * list, we could see a termination bit
 183                                 * prematurely unless it fully inits the sg
 184                                 * table on each mapping. We KNOW that there
 185                                 * must be more entries here or the driver
 186                                 * would be buggy, so force clear the
 187                                 * termination bit to avoid doing a full
 188                                 * sg_init_table() in drivers for each command.
 189                                 */
 190                                sg->page_link &= ~0x02;
 191                                sg = sg_next(sg);
 192                        }
 193
 194                        sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
 195                        nsegs++;
 196                }
 197                bvprv = bvec;
 198        } /* segments in rq */
 199
 200
 201        if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 202            (rq->data_len & q->dma_pad_mask)) {
 203                unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
 204
 205                sg->length += pad_len;
 206                rq->extra_len += pad_len;
 207        }
 208
 209        if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 210                if (rq->cmd_flags & REQ_RW)
 211                        memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 212
 213                sg->page_link &= ~0x02;
 214                sg = sg_next(sg);
 215                sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 216                            q->dma_drain_size,
 217                            ((unsigned long)q->dma_drain_buffer) &
 218                            (PAGE_SIZE - 1));
 219                nsegs++;
 220                rq->extra_len += q->dma_drain_size;
 221        }
 222
 223        if (sg)
 224                sg_mark_end(sg);
 225
 226        return nsegs;
 227}
 228EXPORT_SYMBOL(blk_rq_map_sg);
 229
 230static inline int ll_new_hw_segment(struct request_queue *q,
 231                                    struct request *req,
 232                                    struct bio *bio)
 233{
 234        int nr_phys_segs = bio_phys_segments(q, bio);
 235
 236        if (req->nr_phys_segments + nr_phys_segs > q->max_hw_segments
 237            || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
 238                req->cmd_flags |= REQ_NOMERGE;
 239                if (req == q->last_merge)
 240                        q->last_merge = NULL;
 241                return 0;
 242        }
 243
 244        /*
 245         * This will form the start of a new hw segment.  Bump both
 246         * counters.
 247         */
 248        req->nr_phys_segments += nr_phys_segs;
 249        return 1;
 250}
 251
 252int ll_back_merge_fn(struct request_queue *q, struct request *req,
 253                     struct bio *bio)
 254{
 255        unsigned short max_sectors;
 256
 257        if (unlikely(blk_pc_request(req)))
 258                max_sectors = q->max_hw_sectors;
 259        else
 260                max_sectors = q->max_sectors;
 261
 262        if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
 263                req->cmd_flags |= REQ_NOMERGE;
 264                if (req == q->last_merge)
 265                        q->last_merge = NULL;
 266                return 0;
 267        }
 268        if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 269                blk_recount_segments(q, req->biotail);
 270        if (!bio_flagged(bio, BIO_SEG_VALID))
 271                blk_recount_segments(q, bio);
 272
 273        return ll_new_hw_segment(q, req, bio);
 274}
 275
 276int ll_front_merge_fn(struct request_queue *q, struct request *req,
 277                      struct bio *bio)
 278{
 279        unsigned short max_sectors;
 280
 281        if (unlikely(blk_pc_request(req)))
 282                max_sectors = q->max_hw_sectors;
 283        else
 284                max_sectors = q->max_sectors;
 285
 286
 287        if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
 288                req->cmd_flags |= REQ_NOMERGE;
 289                if (req == q->last_merge)
 290                        q->last_merge = NULL;
 291                return 0;
 292        }
 293        if (!bio_flagged(bio, BIO_SEG_VALID))
 294                blk_recount_segments(q, bio);
 295        if (!bio_flagged(req->bio, BIO_SEG_VALID))
 296                blk_recount_segments(q, req->bio);
 297
 298        return ll_new_hw_segment(q, req, bio);
 299}
 300
 301static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 302                                struct request *next)
 303{
 304        int total_phys_segments;
 305        unsigned int seg_size =
 306                req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 307
 308        /*
 309         * First check if the either of the requests are re-queued
 310         * requests.  Can't merge them if they are.
 311         */
 312        if (req->special || next->special)
 313                return 0;
 314
 315        /*
 316         * Will it become too large?
 317         */
 318        if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
 319                return 0;
 320
 321        total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 322        if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 323                if (req->nr_phys_segments == 1)
 324                        req->bio->bi_seg_front_size = seg_size;
 325                if (next->nr_phys_segments == 1)
 326                        next->biotail->bi_seg_back_size = seg_size;
 327                total_phys_segments--;
 328        }
 329
 330        if (total_phys_segments > q->max_phys_segments)
 331                return 0;
 332
 333        if (total_phys_segments > q->max_hw_segments)
 334                return 0;
 335
 336        /* Merge is OK... */
 337        req->nr_phys_segments = total_phys_segments;
 338        return 1;
 339}
 340
 341/*
 342 * Has to be called with the request spinlock acquired
 343 */
 344static int attempt_merge(struct request_queue *q, struct request *req,
 345                          struct request *next)
 346{
 347        if (!rq_mergeable(req) || !rq_mergeable(next))
 348                return 0;
 349
 350        /*
 351         * not contiguous
 352         */
 353        if (req->sector + req->nr_sectors != next->sector)
 354                return 0;
 355
 356        if (rq_data_dir(req) != rq_data_dir(next)
 357            || req->rq_disk != next->rq_disk
 358            || next->special)
 359                return 0;
 360
 361        if (blk_integrity_rq(req) != blk_integrity_rq(next))
 362                return 0;
 363
 364        /*
 365         * If we are allowed to merge, then append bio list
 366         * from next to rq and release next. merge_requests_fn
 367         * will have updated segment counts, update sector
 368         * counts here.
 369         */
 370        if (!ll_merge_requests_fn(q, req, next))
 371                return 0;
 372
 373        /*
 374         * At this point we have either done a back merge
 375         * or front merge. We need the smaller start_time of
 376         * the merged requests to be the current request
 377         * for accounting purposes.
 378         */
 379        if (time_after(req->start_time, next->start_time))
 380                req->start_time = next->start_time;
 381
 382        req->biotail->bi_next = next->bio;
 383        req->biotail = next->biotail;
 384
 385        req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
 386
 387        elv_merge_requests(q, req, next);
 388
 389        if (req->rq_disk) {
 390                struct hd_struct *part;
 391                int cpu;
 392
 393                cpu = part_stat_lock();
 394                part = disk_map_sector_rcu(req->rq_disk, req->sector);
 395
 396                part_round_stats(cpu, part);
 397                part_dec_in_flight(part);
 398
 399                part_stat_unlock();
 400        }
 401
 402        req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 403        if (blk_rq_cpu_valid(next))
 404                req->cpu = next->cpu;
 405
 406        __blk_put_request(q, next);
 407        return 1;
 408}
 409
 410int attempt_back_merge(struct request_queue *q, struct request *rq)
 411{
 412        struct request *next = elv_latter_request(q, rq);
 413
 414        if (next)
 415                return attempt_merge(q, rq, next);
 416
 417        return 0;
 418}
 419
 420int attempt_front_merge(struct request_queue *q, struct request *rq)
 421{
 422        struct request *prev = elv_former_request(q, rq);
 423
 424        if (prev)
 425                return attempt_merge(q, prev, rq);
 426
 427        return 0;
 428}
 429