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 void 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
  41 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
  42                                              struct bio *bio,
  43                                              unsigned int *seg_size_ptr)
  44 {
  45         unsigned int phys_size;
  46         struct bio_vec *bv, *bvprv = NULL;
  47         int cluster, i, high, highprv = 1;
  48         unsigned int seg_size, nr_phys_segs;
  49         struct bio *fbio;
  50
  51         if (!bio)
  52                 return 0;
  53
  54         fbio = bio;
  55         cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
  56         seg_size = 0;
  57         phys_size = nr_phys_segs = 0;
  58         for_each_bio(bio) {
  59                 bio_for_each_segment(bv, bio, i) {
  60                         /*
  61                          * the trick here is making sure that a high page is
  62                          * never considered part of another segment, since that
  63                          * might change with the bounce page.
  64                          */
  65                         high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
  66                         if (high || highprv)
  67                                 goto new_segment;
  68                         if (cluster) {
  69                                 if (seg_size + bv->bv_len > q->max_segment_size)
  70                                         goto new_segment;
  71                                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
  72                                         goto new_segment;
  73                                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
  74                                         goto new_segment;
  75
  76                                 seg_size += bv->bv_len;
  77                                 bvprv = bv;
  78                                 continue;
  79                         }
  80 new_segment:
  81                         if (nr_phys_segs == 1 && seg_size >
  82                             fbio->bi_seg_front_size)
  83                                 fbio->bi_seg_front_size = seg_size;
  84
  85                         nr_phys_segs++;
  86                         bvprv = bv;
  87                         seg_size = bv->bv_len;
  88                         highprv = high;
  89                 }
  90         }
  91
  92         if (seg_size_ptr)
  93                 *seg_size_ptr = seg_size;
  94
  95         return nr_phys_segs;
  96 }
  97
  98 void blk_recalc_rq_segments(struct request *rq)
  99 {
 100         unsigned int seg_size = 0, phys_segs;
 101
 102         phys_segs = __blk_recalc_rq_segments(rq->q, rq->bio, &seg_size);
 103
 104         if (phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
 105                 rq->bio->bi_seg_front_size = seg_size;
 106         if (seg_size > rq->biotail->bi_seg_back_size)
 107                 rq->biotail->bi_seg_back_size = seg_size;
 108
 109         rq->nr_phys_segments = phys_segs;
 110 }
 111
 112 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 113 {
 114         struct bio *nxt = bio->bi_next;
 115
 116         bio->bi_next = NULL;
 117         bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, NULL);
 118         bio->bi_next = nxt;
 119         bio->bi_flags |= (1 << BIO_SEG_VALID);
 120 }
 121 EXPORT_SYMBOL(blk_recount_segments);
 122
 123 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 124                                    struct bio *nxt)
 125 {
 126         if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
 127                 return 0;
 128
 129         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 130             q->max_segment_size)
 131                 return 0;
 132
 133         if (!bio_has_data(bio))
 134                 return 1;
 135
 136         if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
 137                 return 0;
 138
 139         /*
 140          * bio and nxt are contiguous in memory; check if the queue allows
 141          * these two to be merged into one
 142          */
 143         if (BIO_SEG_BOUNDARY(q, bio, nxt))
 144                 return 1;
 145
 146         return 0;
 147 }
 148
 149 /*
 150  * map a request to scatterlist, return number of sg entries setup. Caller
 151  * must make sure sg can hold rq->nr_phys_segments entries
 152  */
 153 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 154                   struct scatterlist *sglist)
 155 {
 156         struct bio_vec *bvec, *bvprv;
 157         struct req_iterator iter;
 158         struct scatterlist *sg;
 159         int nsegs, cluster;
 160
 161         nsegs = 0;
 162         cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
 163
 164         /*
 165          * for each bio in rq
 166          */
 167         bvprv = NULL;
 168         sg = NULL;
 169         rq_for_each_segment(bvec, rq, iter) {
 170                 int nbytes = bvec->bv_len;
 171
 172                 if (bvprv && cluster) {
 173                         if (sg->length + nbytes > q->max_segment_size)
 174                                 goto new_segment;
 175
 176                         if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 177                                 goto new_segment;
 178                         if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 179                                 goto new_segment;
 180
 181                         sg->length += nbytes;
 182                 } else {
 183 new_segment:
 184                         if (!sg)
 185                                 sg = sglist;
 186                         else {
 187                                 /*
 188                                  * If the driver previously mapped a shorter
 189                                  * list, we could see a termination bit
 190                                  * prematurely unless it fully inits the sg
 191                                  * table on each mapping. We KNOW that there
 192                                  * must be more entries here or the driver
 193                                  * would be buggy, so force clear the
 194                                  * termination bit to avoid doing a full
 195                                  * sg_init_table() in drivers for each command.
 196                                  */
 197                                 sg->page_link &= ~0x02;
 198                                 sg = sg_next(sg);
 199                         }
 200
 201                         sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
 202                         nsegs++;
 203                 }
 204                 bvprv = bvec;
 205         } /* segments in rq */
 206
 207
 208         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 209             (rq->data_len & q->dma_pad_mask)) {
 210                 unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
 211
 212                 sg->length += pad_len;
 213                 rq->extra_len += pad_len;
 214         }
 215
 216         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 217                 if (rq->cmd_flags & REQ_RW)
 218                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 219
 220                 sg->page_link &= ~0x02;
 221                 sg = sg_next(sg);
 222                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 223                             q->dma_drain_size,
 224                             ((unsigned long)q->dma_drain_buffer) &
 225                             (PAGE_SIZE - 1));
 226                 nsegs++;
 227                 rq->extra_len += q->dma_drain_size;
 228         }
 229
 230         if (sg)
 231                 sg_mark_end(sg);
 232
 233         return nsegs;
 234 }
 235 EXPORT_SYMBOL(blk_rq_map_sg);
 236
 237 static inline int ll_new_hw_segment(struct request_queue *q,
 238                                     struct request *req,
 239                                     struct bio *bio)
 240 {
 241         int nr_phys_segs = bio_phys_segments(q, bio);
 242
 243         if (req->nr_phys_segments + nr_phys_segs > q->max_hw_segments
 244             || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
 245                 req->cmd_flags |= REQ_NOMERGE;
 246                 if (req == q->last_merge)
 247                         q->last_merge = NULL;
 248                 return 0;
 249         }
 250
 251         /*
 252          * This will form the start of a new hw segment.  Bump both
 253          * counters.
 254          */
 255         req->nr_phys_segments += nr_phys_segs;
 256         return 1;
 257 }
 258
 259 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 260                      struct bio *bio)
 261 {
 262         unsigned short max_sectors;
 263
 264         if (unlikely(blk_pc_request(req)))
 265                 max_sectors = q->max_hw_sectors;
 266         else
 267                 max_sectors = q->max_sectors;
 268
 269         if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
 270                 req->cmd_flags |= REQ_NOMERGE;
 271                 if (req == q->last_merge)
 272                         q->last_merge = NULL;
 273                 return 0;
 274         }
 275         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 276                 blk_recount_segments(q, req->biotail);
 277         if (!bio_flagged(bio, BIO_SEG_VALID))
 278                 blk_recount_segments(q, bio);
 279
 280         return ll_new_hw_segment(q, req, bio);
 281 }
 282
 283 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 284                       struct bio *bio)
 285 {
 286         unsigned short max_sectors;
 287
 288         if (unlikely(blk_pc_request(req)))
 289                 max_sectors = q->max_hw_sectors;
 290         else
 291                 max_sectors = q->max_sectors;
 292
 293
 294         if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
 295                 req->cmd_flags |= REQ_NOMERGE;
 296                 if (req == q->last_merge)
 297                         q->last_merge = NULL;
 298                 return 0;
 299         }
 300         if (!bio_flagged(bio, BIO_SEG_VALID))
 301                 blk_recount_segments(q, bio);
 302         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 303                 blk_recount_segments(q, req->bio);
 304
 305         return ll_new_hw_segment(q, req, bio);
 306 }
 307
 308 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 309                                 struct request *next)
 310 {
 311         int total_phys_segments;
 312         unsigned int seg_size =
 313                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 314
 315         /*
 316          * First check if the either of the requests are re-queued
 317          * requests.  Can't merge them if they are.
 318          */
 319         if (req->special || next->special)
 320                 return 0;
 321
 322         /*
 323          * Will it become too large?
 324          */
 325         if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
 326                 return 0;
 327
 328         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 329         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 330                 if (req->nr_phys_segments == 1)
 331                         req->bio->bi_seg_front_size = seg_size;
 332                 if (next->nr_phys_segments == 1)
 333                         next->biotail->bi_seg_back_size = seg_size;
 334                 total_phys_segments--;
 335         }
 336
 337         if (total_phys_segments > q->max_phys_segments)
 338                 return 0;
 339
 340         if (total_phys_segments > q->max_hw_segments)
 341                 return 0;
 342
 343         /* Merge is OK... */
 344         req->nr_phys_segments = total_phys_segments;
 345         return 1;
 346 }
 347
 348 /*
 349  * Has to be called with the request spinlock acquired
 350  */
 351 static int attempt_merge(struct request_queue *q, struct request *req,
 352                           struct request *next)
 353 {
 354         if (!rq_mergeable(req) || !rq_mergeable(next))
 355                 return 0;
 356
 357         /*
 358          * not contiguous
 359          */
 360         if (req->sector + req->nr_sectors != next->sector)
 361                 return 0;
 362
 363         if (rq_data_dir(req) != rq_data_dir(next)
 364             || req->rq_disk != next->rq_disk
 365             || next->special)
 366                 return 0;
 367
 368         if (blk_integrity_rq(req) != blk_integrity_rq(next))
 369                 return 0;
 370
 371         /*
 372          * If we are allowed to merge, then append bio list
 373          * from next to rq and release next. merge_requests_fn
 374          * will have updated segment counts, update sector
 375          * counts here.
 376          */
 377         if (!ll_merge_requests_fn(q, req, next))
 378                 return 0;
 379
 380         /*
 381          * At this point we have either done a back merge
 382          * or front merge. We need the smaller start_time of
 383          * the merged requests to be the current request
 384          * for accounting purposes.
 385          */
 386         if (time_after(req->start_time, next->start_time))
 387                 req->start_time = next->start_time;
 388
 389         req->biotail->bi_next = next->bio;
 390         req->biotail = next->biotail;
 391
 392         req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
 393
 394         elv_merge_requests(q, req, next);
 395
 396         if (req->rq_disk) {
 397                 struct hd_struct *part;
 398                 int cpu;
 399
 400                 cpu = part_stat_lock();
 401                 part = disk_map_sector_rcu(req->rq_disk, req->sector);
 402
 403                 part_round_stats(cpu, part);
 404                 part_dec_in_flight(part);
 405
 406                 part_stat_unlock();
 407         }
 408
 409         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 410         if (blk_rq_cpu_valid(next))
 411                 req->cpu = next->cpu;
 412
 413         __blk_put_request(q, next);
 414         return 1;
 415 }
 416
 417 int attempt_back_merge(struct request_queue *q, struct request *rq)
 418 {
 419         struct request *next = elv_latter_request(q, rq);
 420
 421         if (next)
 422                 return attempt_merge(q, rq, next);
 423
 424         return 0;
 425 }
 426
 427 int attempt_front_merge(struct request_queue *q, struct request *rq)
 428 {
 429         struct request *prev = elv_former_request(q, rq);
 430
 431         if (prev)
 432                 return attempt_merge(q, prev, rq);
 433
 434         return 0;
 435 }