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) { 224 sg->page_link &= ~0x02; 225 sg = sg_next(sg); 226 sg_set_page(sg, virt_to_page(q->dma_drain_buffer), 227 q->dma_drain_size, 228 ((unsigned long)q->dma_drain_buffer) & 229 (PAGE_SIZE - 1)); 230 nsegs++; 231 } 232 233 if (sg) 234 sg_mark_end(sg); 235 236 return nsegs; 237 } 238 EXPORT_SYMBOL(blk_rq_map_sg); 239 240 static inline int ll_new_mergeable(struct request_queue *q, 241 struct request *req, 242 struct bio *bio) 243 { 244 int nr_phys_segs = bio_phys_segments(q, bio); 245 246 if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) { 247 req->cmd_flags |= REQ_NOMERGE; 248 if (req == q->last_merge) 249 q->last_merge = NULL; 250 return 0; 251 } 252 253 /* 254 * A hw segment is just getting larger, bump just the phys 255 * counter. 256 */ 257 req->nr_phys_segments += nr_phys_segs; 258 return 1; 259 } 260 261 static inline int ll_new_hw_segment(struct request_queue *q, 262 struct request *req, 263 struct bio *bio) 264 { 265 int nr_hw_segs = bio_hw_segments(q, bio); 266 int nr_phys_segs = bio_phys_segments(q, bio); 267 268 if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments 269 || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) { 270 req->cmd_flags |= REQ_NOMERGE; 271 if (req == q->last_merge) 272 q->last_merge = NULL; 273 return 0; 274 } 275 276 /* 277 * This will form the start of a new hw segment. Bump both 278 * counters. 279 */ 280 req->nr_hw_segments += nr_hw_segs; 281 req->nr_phys_segments += nr_phys_segs; 282 return 1; 283 } 284 285 int ll_back_merge_fn(struct request_queue *q, struct request *req, 286 struct bio *bio) 287 { 288 unsigned short max_sectors; 289 int len; 290 291 if (unlikely(blk_pc_request(req))) 292 max_sectors = q->max_hw_sectors; 293 else 294 max_sectors = q->max_sectors; 295 296 if (req->nr_sectors + bio_sectors(bio) > max_sectors) { 297 req->cmd_flags |= REQ_NOMERGE; 298 if (req == q->last_merge) 299 q->last_merge = NULL; 300 return 0; 301 } 302 if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID))) 303 blk_recount_segments(q, req->biotail); 304 if (unlikely(!bio_flagged(bio, BIO_SEG_VALID))) 305 blk_recount_segments(q, bio); 306 len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size; 307 if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio)) 308 && !BIOVEC_VIRT_OVERSIZE(len)) { 309 int mergeable = ll_new_mergeable(q, req, bio); 310 311 if (mergeable) { 312 if (req->nr_hw_segments == 1) 313 req->bio->bi_hw_front_size = len; 314 if (bio->bi_hw_segments == 1) 315 bio->bi_hw_back_size = len; 316 } 317 return mergeable; 318 } 319 320 return ll_new_hw_segment(q, req, bio); 321 } 322 323 int ll_front_merge_fn(struct request_queue *q, struct request *req, 324 struct bio *bio) 325 { 326 unsigned short max_sectors; 327 int len; 328 329 if (unlikely(blk_pc_request(req))) 330 max_sectors = q->max_hw_sectors; 331 else 332 max_sectors = q->max_sectors; 333 334 335 if (req->nr_sectors + bio_sectors(bio) > max_sectors) { 336 req->cmd_flags |= REQ_NOMERGE; 337 if (req == q->last_merge) 338 q->last_merge = NULL; 339 return 0; 340 } 341 len = bio->bi_hw_back_size + req->bio->bi_hw_front_size; 342 if (unlikely(!bio_flagged(bio, BIO_SEG_VALID))) 343 blk_recount_segments(q, bio); 344 if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID))) 345 blk_recount_segments(q, req->bio); 346 if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) && 347 !BIOVEC_VIRT_OVERSIZE(len)) { 348 int mergeable = ll_new_mergeable(q, req, bio); 349 350 if (mergeable) { 351 if (bio->bi_hw_segments == 1) 352 bio->bi_hw_front_size = len; 353 if (req->nr_hw_segments == 1) 354 req->biotail->bi_hw_back_size = len; 355 } 356 return mergeable; 357 } 358 359 return ll_new_hw_segment(q, req, bio); 360 } 361 362 static int ll_merge_requests_fn(struct request_queue *q, struct request *req, 363 struct request *next) 364 { 365 int total_phys_segments; 366 int total_hw_segments; 367 368 /* 369 * First check if the either of the requests are re-queued 370 * requests. Can't merge them if they are. 371 */ 372 if (req->special || next->special) 373 return 0; 374 375 /* 376 * Will it become too large? 377 */ 378 if ((req->nr_sectors + next->nr_sectors) > q->max_sectors) 379 return 0; 380 381 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; 382 if (blk_phys_contig_segment(q, req->biotail, next->bio)) 383 total_phys_segments--; 384 385 if (total_phys_segments > q->max_phys_segments) 386 return 0; 387 388 total_hw_segments = req->nr_hw_segments + next->nr_hw_segments; 389 if (blk_hw_contig_segment(q, req->biotail, next->bio)) { 390 int len = req->biotail->bi_hw_back_size + 391 next->bio->bi_hw_front_size; 392 /* 393 * propagate the combined length to the end of the requests 394 */ 395 if (req->nr_hw_segments == 1) 396 req->bio->bi_hw_front_size = len; 397 if (next->nr_hw_segments == 1) 398 next->biotail->bi_hw_back_size = len; 399 total_hw_segments--; 400 } 401 402 if (total_hw_segments > q->max_hw_segments) 403 return 0; 404 405 /* Merge is OK... */ 406 req->nr_phys_segments = total_phys_segments; 407 req->nr_hw_segments = total_hw_segments; 408 return 1; 409 } 410 411 /* 412 * Has to be called with the request spinlock acquired 413 */ 414 static int attempt_merge(struct request_queue *q, struct request *req, 415 struct request *next) 416 { 417 if (!rq_mergeable(req) || !rq_mergeable(next)) 418 return 0; 419 420 /* 421 * not contiguous 422 */ 423 if (req->sector + req->nr_sectors != next->sector) 424 return 0; 425 426 if (rq_data_dir(req) != rq_data_dir(next) 427 || req->rq_disk != next->rq_disk 428 || next->special) 429 return 0; 430 431 /* 432 * If we are allowed to merge, then append bio list 433 * from next to rq and release next. merge_requests_fn 434 * will have updated segment counts, update sector 435 * counts here. 436 */ 437 if (!ll_merge_requests_fn(q, req, next)) 438 return 0; 439 440 /* 441 * At this point we have either done a back merge 442 * or front merge. We need the smaller start_time of 443 * the merged requests to be the current request 444 * for accounting purposes. 445 */ 446 if (time_after(req->start_time, next->start_time)) 447 req->start_time = next->start_time; 448 449 req->biotail->bi_next = next->bio; 450 req->biotail = next->biotail; 451 452 req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors; 453 454 elv_merge_requests(q, req, next); 455 456 if (req->rq_disk) { 457 disk_round_stats(req->rq_disk); 458 req->rq_disk->in_flight--; 459 } 460 461 req->ioprio = ioprio_best(req->ioprio, next->ioprio); 462 463 __blk_put_request(q, next); 464 return 1; 465 } 466 467 int attempt_back_merge(struct request_queue *q, struct request *rq) 468 { 469 struct request *next = elv_latter_request(q, rq); 470 471 if (next) 472 return attempt_merge(q, rq, next); 473 474 return 0; 475 } 476 477 int attempt_front_merge(struct request_queue *q, struct request *rq) 478 { 479 struct request *prev = elv_former_request(q, rq); 480 481 if (prev) 482 return attempt_merge(q, prev, rq); 483 484 return 0; 485 } 486