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_WRITE) 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_segments(q)) { 210 req->cmd_flags |= REQ_NOMERGE; 211 if (req == q->last_merge) 212 q->last_merge = NULL; 213 return 0; 214 } 215 216 /* 217 * This will form the start of a new hw segment. Bump both 218 * counters. 219 */ 220 req->nr_phys_segments += nr_phys_segs; 221 return 1; 222 } 223 224 int ll_back_merge_fn(struct request_queue *q, struct request *req, 225 struct bio *bio) 226 { 227 unsigned short max_sectors; 228 229 if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC)) 230 max_sectors = queue_max_hw_sectors(q); 231 else 232 max_sectors = queue_max_sectors(q); 233 234 if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) { 235 req->cmd_flags |= REQ_NOMERGE; 236 if (req == q->last_merge) 237 q->last_merge = NULL; 238 return 0; 239 } 240 if (!bio_flagged(req->biotail, BIO_SEG_VALID)) 241 blk_recount_segments(q, req->biotail); 242 if (!bio_flagged(bio, BIO_SEG_VALID)) 243 blk_recount_segments(q, bio); 244 245 return ll_new_hw_segment(q, req, bio); 246 } 247 248 int ll_front_merge_fn(struct request_queue *q, struct request *req, 249 struct bio *bio) 250 { 251 unsigned short max_sectors; 252 253 if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC)) 254 max_sectors = queue_max_hw_sectors(q); 255 else 256 max_sectors = queue_max_sectors(q); 257 258 259 if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) { 260 req->cmd_flags |= REQ_NOMERGE; 261 if (req == q->last_merge) 262 q->last_merge = NULL; 263 return 0; 264 } 265 if (!bio_flagged(bio, BIO_SEG_VALID)) 266 blk_recount_segments(q, bio); 267 if (!bio_flagged(req->bio, BIO_SEG_VALID)) 268 blk_recount_segments(q, req->bio); 269 270 return ll_new_hw_segment(q, req, bio); 271 } 272 273 static int ll_merge_requests_fn(struct request_queue *q, struct request *req, 274 struct request *next) 275 { 276 int total_phys_segments; 277 unsigned int seg_size = 278 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size; 279 280 /* 281 * First check if the either of the requests are re-queued 282 * requests. Can't merge them if they are. 283 */ 284 if (req->special || next->special) 285 return 0; 286 287 /* 288 * Will it become too large? 289 */ 290 if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q)) 291 return 0; 292 293 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; 294 if (blk_phys_contig_segment(q, req->biotail, next->bio)) { 295 if (req->nr_phys_segments == 1) 296 req->bio->bi_seg_front_size = seg_size; 297 if (next->nr_phys_segments == 1) 298 next->biotail->bi_seg_back_size = seg_size; 299 total_phys_segments--; 300 } 301 302 if (total_phys_segments > queue_max_segments(q)) 303 return 0; 304 305 /* Merge is OK... */ 306 req->nr_phys_segments = total_phys_segments; 307 return 1; 308 } 309 310 /** 311 * blk_rq_set_mixed_merge - mark a request as mixed merge 312 * @rq: request to mark as mixed merge 313 * 314 * Description: 315 * @rq is about to be mixed merged. Make sure the attributes 316 * which can be mixed are set in each bio and mark @rq as mixed 317 * merged. 318 */ 319 void blk_rq_set_mixed_merge(struct request *rq) 320 { 321 unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK; 322 struct bio *bio; 323 324 if (rq->cmd_flags & REQ_MIXED_MERGE) 325 return; 326 327 /* 328 * @rq will no longer represent mixable attributes for all the 329 * contained bios. It will just track those of the first one. 330 * Distributes the attributs to each bio. 331 */ 332 for (bio = rq->bio; bio; bio = bio->bi_next) { 333 WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) && 334 (bio->bi_rw & REQ_FAILFAST_MASK) != ff); 335 bio->bi_rw |= ff; 336 } 337 rq->cmd_flags |= REQ_MIXED_MERGE; 338 } 339 340 static void blk_account_io_merge(struct request *req) 341 { 342 if (blk_do_io_stat(req)) { 343 struct hd_struct *part; 344 int cpu; 345 346 cpu = part_stat_lock(); 347 part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); 348 349 part_round_stats(cpu, part); 350 part_dec_in_flight(part, rq_data_dir(req)); 351 352 part_stat_unlock(); 353 } 354 } 355 356 /* 357 * Has to be called with the request spinlock acquired 358 */ 359 static int attempt_merge(struct request_queue *q, struct request *req, 360 struct request *next) 361 { 362 if (!rq_mergeable(req) || !rq_mergeable(next)) 363 return 0; 364 365 /* 366 * not contiguous 367 */ 368 if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) 369 return 0; 370 371 if (rq_data_dir(req) != rq_data_dir(next) 372 || req->rq_disk != next->rq_disk 373 || next->special) 374 return 0; 375 376 if (blk_integrity_rq(req) != blk_integrity_rq(next)) 377 return 0; 378 379 /* 380 * If we are allowed to merge, then append bio list 381 * from next to rq and release next. merge_requests_fn 382 * will have updated segment counts, update sector 383 * counts here. 384 */ 385 if (!ll_merge_requests_fn(q, req, next)) 386 return 0; 387 388 /* 389 * If failfast settings disagree or any of the two is already 390 * a mixed merge, mark both as mixed before proceeding. This 391 * makes sure that all involved bios have mixable attributes 392 * set properly. 393 */ 394 if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE || 395 (req->cmd_flags & REQ_FAILFAST_MASK) != 396 (next->cmd_flags & REQ_FAILFAST_MASK)) { 397 blk_rq_set_mixed_merge(req); 398 blk_rq_set_mixed_merge(next); 399 } 400 401 /* 402 * At this point we have either done a back merge 403 * or front merge. We need the smaller start_time of 404 * the merged requests to be the current request 405 * for accounting purposes. 406 */ 407 if (time_after(req->start_time, next->start_time)) 408 req->start_time = next->start_time; 409 410 req->biotail->bi_next = next->bio; 411 req->biotail = next->biotail; 412 413 req->__data_len += blk_rq_bytes(next); 414 415 elv_merge_requests(q, req, next); 416 417 /* 418 * 'next' is going away, so update stats accordingly 419 */ 420 blk_account_io_merge(next); 421 422 req->ioprio = ioprio_best(req->ioprio, next->ioprio); 423 if (blk_rq_cpu_valid(next)) 424 req->cpu = next->cpu; 425 426 /* owner-ship of bio passed from next to req */ 427 next->bio = NULL; 428 __blk_put_request(q, next); 429 return 1; 430 } 431 432 int attempt_back_merge(struct request_queue *q, struct request *rq) 433 { 434 struct request *next = elv_latter_request(q, rq); 435 436 if (next) 437 return attempt_merge(q, rq, next); 438 439 return 0; 440 } 441 442 int attempt_front_merge(struct request_queue *q, struct request *rq) 443 { 444 struct request *prev = elv_former_request(q, rq); 445 446 if (prev) 447 return attempt_merge(q, prev, rq); 448 449 return 0; 450 } 451