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