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 void 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                 }
  79 new_segment:
  80                 nr_phys_segs++;
  81                 bvprv = bv;
  82                 seg_size = bv->bv_len;
  83                 highprv = high;
  84         }
  85
  86         rq->nr_phys_segments = nr_phys_segs;
  87 }
  88
  89 void blk_recount_segments(struct request_queue *q, struct bio *bio)
  90 {
  91         struct request rq;
  92         struct bio *nxt = bio->bi_next;
  93         rq.q = q;
  94         rq.bio = rq.biotail = bio;
  95         bio->bi_next = NULL;
  96         blk_recalc_rq_segments(&rq);
  97         bio->bi_next = nxt;
  98         bio->bi_phys_segments = rq.nr_phys_segments;
  99         bio->bi_flags |= (1 << BIO_SEG_VALID);
 100 }
 101 EXPORT_SYMBOL(blk_recount_segments);
 102
 103 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 104                                    struct bio *nxt)
 105 {
 106         if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
 107                 return 0;
 108
 109         if (bio->bi_size + nxt->bi_size > q->max_segment_size)
 110                 return 0;
 111
 112         if (!bio_has_data(bio))
 113                 return 1;
 114
 115         if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
 116                 return 0;
 117
 118         /*
 119          * bio and nxt are contiguous in memory; check if the queue allows
 120          * these two to be merged into one
 121          */
 122         if (BIO_SEG_BOUNDARY(q, bio, nxt))
 123                 return 1;
 124
 125         return 0;
 126 }
 127
 128 /*
 129  * map a request to scatterlist, return number of sg entries setup. Caller
 130  * must make sure sg can hold rq->nr_phys_segments entries
 131  */
 132 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 133                   struct scatterlist *sglist)
 134 {
 135         struct bio_vec *bvec, *bvprv;
 136         struct req_iterator iter;
 137         struct scatterlist *sg;
 138         int nsegs, cluster;
 139
 140         nsegs = 0;
 141         cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
 142
 143         /*
 144          * for each bio in rq
 145          */
 146         bvprv = NULL;
 147         sg = NULL;
 148         rq_for_each_segment(bvec, rq, iter) {
 149                 int nbytes = bvec->bv_len;
 150
 151                 if (bvprv && cluster) {
 152                         if (sg->length + nbytes > q->max_segment_size)
 153                                 goto new_segment;
 154
 155                         if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 156                                 goto new_segment;
 157                         if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 158                                 goto new_segment;
 159
 160                         sg->length += nbytes;
 161                 } else {
 162 new_segment:
 163                         if (!sg)
 164                                 sg = sglist;
 165                         else {
 166                                 /*
 167                                  * If the driver previously mapped a shorter
 168                                  * list, we could see a termination bit
 169                                  * prematurely unless it fully inits the sg
 170                                  * table on each mapping. We KNOW that there
 171                                  * must be more entries here or the driver
 172                                  * would be buggy, so force clear the
 173                                  * termination bit to avoid doing a full
 174                                  * sg_init_table() in drivers for each command.
 175                                  */
 176                                 sg->page_link &= ~0x02;
 177                                 sg = sg_next(sg);
 178                         }
 179
 180                         sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
 181                         nsegs++;
 182                 }
 183                 bvprv = bvec;
 184         } /* segments in rq */
 185
 186
 187         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 188             (rq->data_len & q->dma_pad_mask)) {
 189                 unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
 190
 191                 sg->length += pad_len;
 192                 rq->extra_len += pad_len;
 193         }
 194
 195         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 196                 if (rq->cmd_flags & REQ_RW)
 197                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 198
 199                 sg->page_link &= ~0x02;
 200                 sg = sg_next(sg);
 201                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 202                             q->dma_drain_size,
 203                             ((unsigned long)q->dma_drain_buffer) &
 204                             (PAGE_SIZE - 1));
 205                 nsegs++;
 206                 rq->extra_len += q->dma_drain_size;
 207         }
 208
 209         if (sg)
 210                 sg_mark_end(sg);
 211
 212         return nsegs;
 213 }
 214 EXPORT_SYMBOL(blk_rq_map_sg);
 215
 216 static inline int ll_new_mergeable(struct request_queue *q,
 217                                    struct request *req,
 218                                    struct bio *bio)
 219 {
 220         int nr_phys_segs = bio_phys_segments(q, bio);
 221
 222         if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
 223                 req->cmd_flags |= REQ_NOMERGE;
 224                 if (req == q->last_merge)
 225                         q->last_merge = NULL;
 226                 return 0;
 227         }
 228
 229         /*
 230          * A hw segment is just getting larger, bump just the phys
 231          * counter.
 232          */
 233         req->nr_phys_segments += nr_phys_segs;
 234         return 1;
 235 }
 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
 313         /*
 314          * First check if the either of the requests are re-queued
 315          * requests.  Can't merge them if they are.
 316          */
 317         if (req->special || next->special)
 318                 return 0;
 319
 320         /*
 321          * Will it become too large?
 322          */
 323         if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
 324                 return 0;
 325
 326         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 327         if (blk_phys_contig_segment(q, req->biotail, next->bio))
 328                 total_phys_segments--;
 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  */
 344 static 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
 410 int 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
 420 int 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 }