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