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)) { 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 int nr_hw_segs; 45 unsigned int phys_size; 46 unsigned int hw_size; 47 struct bio_vec *bv, *bvprv = NULL; 48 int seg_size; 49 int hw_seg_size; 50 int cluster; 51 struct req_iterator iter; 52 int high, highprv = 1; 53 struct request_queue *q = rq->q; 54 55 if (!rq->bio) 56 return; 57 58 cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER); 59 hw_seg_size = seg_size = 0; 60 phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0; 61 rq_for_each_segment(bv, rq, iter) { 62 /* 63 * the trick here is making sure that a high page is never 64 * considered part of another segment, since that might 65 * change with the bounce page. 66 */ 67 high = page_to_pfn(bv->bv_page) > q->bounce_pfn; 68 if (high || highprv) 69 goto new_hw_segment; 70 if (cluster) { 71 if (seg_size + bv->bv_len > q->max_segment_size) 72 goto new_segment; 73 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv)) 74 goto new_segment; 75 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv)) 76 goto new_segment; 77 if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len)) 78 goto new_hw_segment; 79 80 seg_size += bv->bv_len; 81 hw_seg_size += bv->bv_len; 82 bvprv = bv; 83 continue; 84 } 85 new_segment: 86 if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) && 87 !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len)) 88 hw_seg_size += bv->bv_len; 89 else { 90 new_hw_segment: 91 if (nr_hw_segs == 1 && 92 hw_seg_size > rq->bio->bi_hw_front_size) 93 rq->bio->bi_hw_front_size = hw_seg_size; 94 hw_seg_size = BIOVEC_VIRT_START_SIZE(bv) + bv->bv_len; 95 nr_hw_segs++; 96 } 97 98 nr_phys_segs++; 99 bvprv = bv; 100 seg_size = bv->bv_len; 101 highprv = high; 102 } 103 104 if (nr_hw_segs == 1 && 105 hw_seg_size > rq->bio->bi_hw_front_size) 106 rq->bio->bi_hw_front_size = hw_seg_size; 107 if (hw_seg_size > rq->biotail->bi_hw_back_size) 108 rq->biotail->bi_hw_back_size = hw_seg_size; 109 rq->nr_phys_segments = nr_phys_segs; 110 rq->nr_hw_segments = nr_hw_segs; 111 } 112 113 void blk_recount_segments(struct request_queue *q, struct bio *bio) 114 { 115 struct request rq; 116 struct bio *nxt = bio->bi_next; 117 rq.q = q; 118 rq.bio = rq.biotail = bio; 119 bio->bi_next = NULL; 120 blk_recalc_rq_segments(&rq); 121 bio->bi_next = nxt; 122 bio->bi_phys_segments = rq.nr_phys_segments; 123 bio->bi_hw_segments = rq.nr_hw_segments; 124 bio->bi_flags |= (1 << BIO_SEG_VALID); 125 } 126 EXPORT_SYMBOL(blk_recount_segments); 127 128 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio, 129 struct bio *nxt) 130 { 131 if (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER))) 132 return 0; 133 134 if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt))) 135 return 0; 136 if (bio->bi_size + nxt->bi_size > q->max_segment_size) 137 return 0; 138 139 /* 140 * bio and nxt are contigous 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 static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio, 150 struct bio *nxt) 151 { 152 if (unlikely(!bio_flagged(bio, BIO_SEG_VALID))) 153 blk_recount_segments(q, bio); 154 if (unlikely(!bio_flagged(nxt, BIO_SEG_VALID))) 155 blk_recount_segments(q, nxt); 156 if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) || 157 BIOVEC_VIRT_OVERSIZE(bio->bi_hw_back_size + nxt->bi_hw_front_size)) 158 return 0; 159 if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size) 160 return 0; 161 162 return 1; 163 } 164 165 /* 166 * map a request to scatterlist, return number of sg entries setup. Caller 167 * must make sure sg can hold rq->nr_phys_segments entries 168 */ 169 int blk_rq_map_sg(struct request_queue *q, struct request *rq, 170 struct scatterlist *sglist) 171 { 172 struct bio_vec *bvec, *bvprv; 173 struct req_iterator iter; 174 struct scatterlist *sg; 175 int nsegs, cluster; 176 177 nsegs = 0; 178 cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER); 179 180 /* 181 * for each bio in rq 182 */ 183 bvprv = NULL; 184 sg = NULL; 185 rq_for_each_segment(bvec, rq, iter) { 186 int nbytes = bvec->bv_len; 187 188 if (bvprv && cluster) { 189 if (sg->length + nbytes > q->max_segment_size) 190 goto new_segment; 191 192 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec)) 193 goto new_segment; 194 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec)) 195 goto new_segment; 196 197 sg->length += nbytes; 198 } else { 199 new_segment: 200 if (!sg) 201 sg = sglist; 202 else { 203 /* 204 * If the driver previously mapped a shorter 205 * list, we could see a termination bit 206 * prematurely unless it fully inits the sg 207 * table on each mapping. We KNOW that there 208 * must be more entries here or the driver 209 * would be buggy, so force clear the 210 * termination bit to avoid doing a full 211 * sg_init_table() in drivers for each command. 212 */ 213 sg->page_link &= ~0x02; 214 sg = sg_next(sg); 215 } 216 217 sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset); 218 nsegs++; 219 } 220 bvprv = bvec; 221 } /* segments in rq */ 222 223 if (q->dma_drain_size && q->dma_drain_needed(rq)) { 224 if (rq->cmd_flags & REQ_RW) 225 memset(q->dma_drain_buffer, 0, q->dma_drain_size); 226 227 sg->page_link &= ~0x02; 228 sg = sg_next(sg); 229 sg_set_page(sg, virt_to_page(q->dma_drain_buffer), 230 q->dma_drain_size, 231 ((unsigned long)q->dma_drain_buffer) & 232 (PAGE_SIZE - 1)); 233 nsegs++; 234 rq->extra_len += q->dma_drain_size; 235 } 236 237 if (sg) 238 sg_mark_end(sg); 239 240 return nsegs; 241 } 242 EXPORT_SYMBOL(blk_rq_map_sg); 243 244 static inline int ll_new_mergeable(struct request_queue *q, 245 struct request *req, 246 struct bio *bio) 247 { 248 int nr_phys_segs = bio_phys_segments(q, bio); 249 250 if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) { 251 req->cmd_flags |= REQ_NOMERGE; 252 if (req == q->last_merge) 253 q->last_merge = NULL; 254 return 0; 255 } 256 257 /* 258 * A hw segment is just getting larger, bump just the phys 259 * counter. 260 */ 261 req->nr_phys_segments += nr_phys_segs; 262 return 1; 263 } 264 265 static inline int ll_new_hw_segment(struct request_queue *q, 266 struct request *req, 267 struct bio *bio) 268 { 269 int nr_hw_segs = bio_hw_segments(q, bio); 270 int nr_phys_segs = bio_phys_segments(q, bio); 271 272 if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments 273 || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) { 274 req->cmd_flags |= REQ_NOMERGE; 275 if (req == q->last_merge) 276 q->last_merge = NULL; 277 return 0; 278 } 279 280 /* 281 * This will form the start of a new hw segment. Bump both 282 * counters. 283 */ 284 req->nr_hw_segments += nr_hw_segs; 285 req->nr_phys_segments += nr_phys_segs; 286 return 1; 287 } 288 289 int ll_back_merge_fn(struct request_queue *q, struct request *req, 290 struct bio *bio) 291 { 292 unsigned short max_sectors; 293 int len; 294 295 if (unlikely(blk_pc_request(req))) 296 max_sectors = q->max_hw_sectors; 297 else 298 max_sectors = q->max_sectors; 299 300 if (req->nr_sectors + bio_sectors(bio) > max_sectors) { 301 req->cmd_flags |= REQ_NOMERGE; 302 if (req == q->last_merge) 303 q->last_merge = NULL; 304 return 0; 305 } 306 if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID))) 307 blk_recount_segments(q, req->biotail); 308 if (unlikely(!bio_flagged(bio, BIO_SEG_VALID))) 309 blk_recount_segments(q, bio); 310 len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size; 311 if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio)) 312 && !BIOVEC_VIRT_OVERSIZE(len)) { 313 int mergeable = ll_new_mergeable(q, req, bio); 314 315 if (mergeable) { 316 if (req->nr_hw_segments == 1) 317 req->bio->bi_hw_front_size = len; 318 if (bio->bi_hw_segments == 1) 319 bio->bi_hw_back_size = len; 320 } 321 return mergeable; 322 } 323 324 return ll_new_hw_segment(q, req, bio); 325 } 326 327 int ll_front_merge_fn(struct request_queue *q, struct request *req, 328 struct bio *bio) 329 { 330 unsigned short max_sectors; 331 int len; 332 333 if (unlikely(blk_pc_request(req))) 334 max_sectors = q->max_hw_sectors; 335 else 336 max_sectors = q->max_sectors; 337 338 339 if (req->nr_sectors + bio_sectors(bio) > max_sectors) { 340 req->cmd_flags |= REQ_NOMERGE; 341 if (req == q->last_merge) 342 q->last_merge = NULL; 343 return 0; 344 } 345 len = bio->bi_hw_back_size + req->bio->bi_hw_front_size; 346 if (unlikely(!bio_flagged(bio, BIO_SEG_VALID))) 347 blk_recount_segments(q, bio); 348 if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID))) 349 blk_recount_segments(q, req->bio); 350 if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) && 351 !BIOVEC_VIRT_OVERSIZE(len)) { 352 int mergeable = ll_new_mergeable(q, req, bio); 353 354 if (mergeable) { 355 if (bio->bi_hw_segments == 1) 356 bio->bi_hw_front_size = len; 357 if (req->nr_hw_segments == 1) 358 req->biotail->bi_hw_back_size = len; 359 } 360 return mergeable; 361 } 362 363 return ll_new_hw_segment(q, req, bio); 364 } 365 366 static int ll_merge_requests_fn(struct request_queue *q, struct request *req, 367 struct request *next) 368 { 369 int total_phys_segments; 370 int total_hw_segments; 371 372 /* 373 * First check if the either of the requests are re-queued 374 * requests. Can't merge them if they are. 375 */ 376 if (req->special || next->special) 377 return 0; 378 379 /* 380 * Will it become too large? 381 */ 382 if ((req->nr_sectors + next->nr_sectors) > q->max_sectors) 383 return 0; 384 385 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; 386 if (blk_phys_contig_segment(q, req->biotail, next->bio)) 387 total_phys_segments--; 388 389 if (total_phys_segments > q->max_phys_segments) 390 return 0; 391 392 total_hw_segments = req->nr_hw_segments + next->nr_hw_segments; 393 if (blk_hw_contig_segment(q, req->biotail, next->bio)) { 394 int len = req->biotail->bi_hw_back_size + 395 next->bio->bi_hw_front_size; 396 /* 397 * propagate the combined length to the end of the requests 398 */ 399 if (req->nr_hw_segments == 1) 400 req->bio->bi_hw_front_size = len; 401 if (next->nr_hw_segments == 1) 402 next->biotail->bi_hw_back_size = len; 403 total_hw_segments--; 404 } 405 406 if (total_hw_segments > q->max_hw_segments) 407 return 0; 408 409 /* Merge is OK... */ 410 req->nr_phys_segments = total_phys_segments; 411 req->nr_hw_segments = total_hw_segments; 412 return 1; 413 } 414 415 /* 416 * Has to be called with the request spinlock acquired 417 */ 418 static int attempt_merge(struct request_queue *q, struct request *req, 419 struct request *next) 420 { 421 if (!rq_mergeable(req) || !rq_mergeable(next)) 422 return 0; 423 424 /* 425 * not contiguous 426 */ 427 if (req->sector + req->nr_sectors != next->sector) 428 return 0; 429 430 if (rq_data_dir(req) != rq_data_dir(next) 431 || req->rq_disk != next->rq_disk 432 || next->special) 433 return 0; 434 435 /* 436 * If we are allowed to merge, then append bio list 437 * from next to rq and release next. merge_requests_fn 438 * will have updated segment counts, update sector 439 * counts here. 440 */ 441 if (!ll_merge_requests_fn(q, req, next)) 442 return 0; 443 444 /* 445 * At this point we have either done a back merge 446 * or front merge. We need the smaller start_time of 447 * the merged requests to be the current request 448 * for accounting purposes. 449 */ 450 if (time_after(req->start_time, next->start_time)) 451 req->start_time = next->start_time; 452 453 req->biotail->bi_next = next->bio; 454 req->biotail = next->biotail; 455 456 req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors; 457 458 elv_merge_requests(q, req, next); 459 460 if (req->rq_disk) { 461 struct hd_struct *part 462 = get_part(req->rq_disk, req->sector); 463 disk_round_stats(req->rq_disk); 464 req->rq_disk->in_flight--; 465 if (part) { 466 part_round_stats(part); 467 part->in_flight--; 468 } 469 } 470 471 req->ioprio = ioprio_best(req->ioprio, next->ioprio); 472 473 __blk_put_request(q, next); 474 return 1; 475 } 476 477 int attempt_back_merge(struct request_queue *q, struct request *rq) 478 { 479 struct request *next = elv_latter_request(q, rq); 480 481 if (next) 482 return attempt_merge(q, rq, next); 483 484 return 0; 485 } 486 487 int attempt_front_merge(struct request_queue *q, struct request *rq) 488 { 489 struct request *prev = elv_former_request(q, rq); 490 491 if (prev) 492 return attempt_merge(q, prev, rq); 493 494 return 0; 495 } 496