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 struct bio_vec *bv, *bvprv = NULL; 16 int cluster, i, high, highprv = 1; 17 unsigned int seg_size, nr_phys_segs; 18 struct bio *fbio, *bbio; 19 20 if (!bio) 21 return 0; 22 23 fbio = bio; 24 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); 25 seg_size = 0; 26 nr_phys_segs = 0; 27 for_each_bio(bio) { 28 bio_for_each_segment(bv, bio, i) { 29 /* 30 * the trick here is making sure that a high page is 31 * never considered part of another segment, since that 32 * might change with the bounce page. 33 */ 34 high = page_to_pfn(bv->bv_page) > queue_bounce_pfn(q); 35 if (high || highprv) 36 goto new_segment; 37 if (cluster) { 38 if (seg_size + bv->bv_len 39 > queue_max_segment_size(q)) 40 goto new_segment; 41 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv)) 42 goto new_segment; 43 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv)) 44 goto new_segment; 45 46 seg_size += bv->bv_len; 47 bvprv = bv; 48 continue; 49 } 50 new_segment: 51 if (nr_phys_segs == 1 && seg_size > 52 fbio->bi_seg_front_size) 53 fbio->bi_seg_front_size = seg_size; 54 55 nr_phys_segs++; 56 bvprv = bv; 57 seg_size = bv->bv_len; 58 highprv = high; 59 } 60 bbio = bio; 61 } 62 63 if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size) 64 fbio->bi_seg_front_size = seg_size; 65 if (seg_size > bbio->bi_seg_back_size) 66 bbio->bi_seg_back_size = seg_size; 67 68 return nr_phys_segs; 69 } 70 71 void blk_recalc_rq_segments(struct request *rq) 72 { 73 rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio); 74 } 75 76 void blk_recount_segments(struct request_queue *q, struct bio *bio) 77 { 78 struct bio *nxt = bio->bi_next; 79 80 bio->bi_next = NULL; 81 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio); 82 bio->bi_next = nxt; 83 bio->bi_flags |= (1 << BIO_SEG_VALID); 84 } 85 EXPORT_SYMBOL(blk_recount_segments); 86 87 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio, 88 struct bio *nxt) 89 { 90 if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags)) 91 return 0; 92 93 if (bio->bi_seg_back_size + nxt->bi_seg_front_size > 94 queue_max_segment_size(q)) 95 return 0; 96 97 if (!bio_has_data(bio)) 98 return 1; 99 100 if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt))) 101 return 0; 102 103 /* 104 * bio and nxt are contiguous in memory; check if the queue allows 105 * these two to be merged into one 106 */ 107 if (BIO_SEG_BOUNDARY(q, bio, nxt)) 108 return 1; 109 110 return 0; 111 } 112 113 /* 114 * map a request to scatterlist, return number of sg entries setup. Caller 115 * must make sure sg can hold rq->nr_phys_segments entries 116 */ 117 int blk_rq_map_sg(struct request_queue *q, struct request *rq, 118 struct scatterlist *sglist) 119 { 120 struct bio_vec *bvec, *bvprv; 121 struct req_iterator iter; 122 struct scatterlist *sg; 123 int nsegs, cluster; 124 125 nsegs = 0; 126 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); 127 128 /* 129 * for each bio in rq 130 */ 131 bvprv = NULL; 132 sg = NULL; 133 rq_for_each_segment(bvec, rq, iter) { 134 int nbytes = bvec->bv_len; 135 136 if (bvprv && cluster) { 137 if (sg->length + nbytes > queue_max_segment_size(q)) 138 goto new_segment; 139 140 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec)) 141 goto new_segment; 142 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec)) 143 goto new_segment; 144 145 sg->length += nbytes; 146 } else { 147 new_segment: 148 if (!sg) 149 sg = sglist; 150 else { 151 /* 152 * If the driver previously mapped a shorter 153 * list, we could see a termination bit 154 * prematurely unless it fully inits the sg 155 * table on each mapping. We KNOW that there 156 * must be more entries here or the driver 157 * would be buggy, so force clear the 158 * termination bit to avoid doing a full 159 * sg_init_table() in drivers for each command. 160 */ 161 sg->page_link &= ~0x02; 162 sg = sg_next(sg); 163 } 164 165 sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset); 166 nsegs++; 167 } 168 bvprv = bvec; 169 } /* segments in rq */ 170 171 172 if (unlikely(rq->cmd_flags & REQ_COPY_USER) && 173 (blk_rq_bytes(rq) & q->dma_pad_mask)) { 174 unsigned int pad_len = 175 (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1; 176 177 sg->length += pad_len; 178 rq->extra_len += pad_len; 179 } 180 181 if (q->dma_drain_size && q->dma_drain_needed(rq)) { 182 if (rq->cmd_flags & REQ_WRITE) 183 memset(q->dma_drain_buffer, 0, q->dma_drain_size); 184 185 sg->page_link &= ~0x02; 186 sg = sg_next(sg); 187 sg_set_page(sg, virt_to_page(q->dma_drain_buffer), 188 q->dma_drain_size, 189 ((unsigned long)q->dma_drain_buffer) & 190 (PAGE_SIZE - 1)); 191 nsegs++; 192 rq->extra_len += q->dma_drain_size; 193 } 194 195 if (sg) 196 sg_mark_end(sg); 197 198 return nsegs; 199 } 200 EXPORT_SYMBOL(blk_rq_map_sg); 201 202 static inline int ll_new_hw_segment(struct request_queue *q, 203 struct request *req, 204 struct bio *bio) 205 { 206 int nr_phys_segs = bio_phys_segments(q, bio); 207 208 if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q)) { 209 req->cmd_flags |= REQ_NOMERGE; 210 if (req == q->last_merge) 211 q->last_merge = NULL; 212 return 0; 213 } 214 215 /* 216 * This will form the start of a new hw segment. Bump both 217 * counters. 218 */ 219 req->nr_phys_segments += nr_phys_segs; 220 return 1; 221 } 222 223 int ll_back_merge_fn(struct request_queue *q, struct request *req, 224 struct bio *bio) 225 { 226 unsigned short max_sectors; 227 228 if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC)) 229 max_sectors = queue_max_hw_sectors(q); 230 else 231 max_sectors = queue_max_sectors(q); 232 233 if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) { 234 req->cmd_flags |= REQ_NOMERGE; 235 if (req == q->last_merge) 236 q->last_merge = NULL; 237 return 0; 238 } 239 if (!bio_flagged(req->biotail, BIO_SEG_VALID)) 240 blk_recount_segments(q, req->biotail); 241 if (!bio_flagged(bio, BIO_SEG_VALID)) 242 blk_recount_segments(q, bio); 243 244 return ll_new_hw_segment(q, req, bio); 245 } 246 247 int ll_front_merge_fn(struct request_queue *q, struct request *req, 248 struct bio *bio) 249 { 250 unsigned short max_sectors; 251 252 if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC)) 253 max_sectors = queue_max_hw_sectors(q); 254 else 255 max_sectors = queue_max_sectors(q); 256 257 258 if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) { 259 req->cmd_flags |= REQ_NOMERGE; 260 if (req == q->last_merge) 261 q->last_merge = NULL; 262 return 0; 263 } 264 if (!bio_flagged(bio, BIO_SEG_VALID)) 265 blk_recount_segments(q, bio); 266 if (!bio_flagged(req->bio, BIO_SEG_VALID)) 267 blk_recount_segments(q, req->bio); 268 269 return ll_new_hw_segment(q, req, bio); 270 } 271 272 static int ll_merge_requests_fn(struct request_queue *q, struct request *req, 273 struct request *next) 274 { 275 int total_phys_segments; 276 unsigned int seg_size = 277 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size; 278 279 /* 280 * First check if the either of the requests are re-queued 281 * requests. Can't merge them if they are. 282 */ 283 if (req->special || next->special) 284 return 0; 285 286 /* 287 * Will it become too large? 288 */ 289 if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q)) 290 return 0; 291 292 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; 293 if (blk_phys_contig_segment(q, req->biotail, next->bio)) { 294 if (req->nr_phys_segments == 1) 295 req->bio->bi_seg_front_size = seg_size; 296 if (next->nr_phys_segments == 1) 297 next->biotail->bi_seg_back_size = seg_size; 298 total_phys_segments--; 299 } 300 301 if (total_phys_segments > queue_max_segments(q)) 302 return 0; 303 304 /* Merge is OK... */ 305 req->nr_phys_segments = total_phys_segments; 306 return 1; 307 } 308 309 /** 310 * blk_rq_set_mixed_merge - mark a request as mixed merge 311 * @rq: request to mark as mixed merge 312 * 313 * Description: 314 * @rq is about to be mixed merged. Make sure the attributes 315 * which can be mixed are set in each bio and mark @rq as mixed 316 * merged. 317 */ 318 void blk_rq_set_mixed_merge(struct request *rq) 319 { 320 unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK; 321 struct bio *bio; 322 323 if (rq->cmd_flags & REQ_MIXED_MERGE) 324 return; 325 326 /* 327 * @rq will no longer represent mixable attributes for all the 328 * contained bios. It will just track those of the first one. 329 * Distributes the attributs to each bio. 330 */ 331 for (bio = rq->bio; bio; bio = bio->bi_next) { 332 WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) && 333 (bio->bi_rw & REQ_FAILFAST_MASK) != ff); 334 bio->bi_rw |= ff; 335 } 336 rq->cmd_flags |= REQ_MIXED_MERGE; 337 } 338 339 static void blk_account_io_merge(struct request *req) 340 { 341 if (blk_do_io_stat(req)) { 342 struct hd_struct *part; 343 int cpu; 344 345 cpu = part_stat_lock(); 346 part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); 347 348 part_round_stats(cpu, part); 349 part_dec_in_flight(part, rq_data_dir(req)); 350 351 part_stat_unlock(); 352 } 353 } 354 355 /* 356 * Has to be called with the request spinlock acquired 357 */ 358 static int attempt_merge(struct request_queue *q, struct request *req, 359 struct request *next) 360 { 361 if (!rq_mergeable(req) || !rq_mergeable(next)) 362 return 0; 363 364 /* 365 * not contiguous 366 */ 367 if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) 368 return 0; 369 370 if (rq_data_dir(req) != rq_data_dir(next) 371 || req->rq_disk != next->rq_disk 372 || next->special) 373 return 0; 374 375 if (blk_integrity_rq(req) != blk_integrity_rq(next)) 376 return 0; 377 378 /* 379 * If we are allowed to merge, then append bio list 380 * from next to rq and release next. merge_requests_fn 381 * will have updated segment counts, update sector 382 * counts here. 383 */ 384 if (!ll_merge_requests_fn(q, req, next)) 385 return 0; 386 387 /* 388 * If failfast settings disagree or any of the two is already 389 * a mixed merge, mark both as mixed before proceeding. This 390 * makes sure that all involved bios have mixable attributes 391 * set properly. 392 */ 393 if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE || 394 (req->cmd_flags & REQ_FAILFAST_MASK) != 395 (next->cmd_flags & REQ_FAILFAST_MASK)) { 396 blk_rq_set_mixed_merge(req); 397 blk_rq_set_mixed_merge(next); 398 } 399 400 /* 401 * At this point we have either done a back merge 402 * or front merge. We need the smaller start_time of 403 * the merged requests to be the current request 404 * for accounting purposes. 405 */ 406 if (time_after(req->start_time, next->start_time)) 407 req->start_time = next->start_time; 408 409 req->biotail->bi_next = next->bio; 410 req->biotail = next->biotail; 411 412 req->__data_len += blk_rq_bytes(next); 413 414 elv_merge_requests(q, req, next); 415 416 /* 417 * 'next' is going away, so update stats accordingly 418 */ 419 blk_account_io_merge(next); 420 421 req->ioprio = ioprio_best(req->ioprio, next->ioprio); 422 if (blk_rq_cpu_valid(next)) 423 req->cpu = next->cpu; 424 425 /* owner-ship of bio passed from next to req */ 426 next->bio = NULL; 427 __blk_put_request(q, next); 428 return 1; 429 } 430 431 int attempt_back_merge(struct request_queue *q, struct request *rq) 432 { 433 struct request *next = elv_latter_request(q, rq); 434 435 if (next) 436 return attempt_merge(q, rq, next); 437 438 return 0; 439 } 440 441 int attempt_front_merge(struct request_queue *q, struct request *rq) 442 { 443 struct request *prev = elv_former_request(q, rq); 444 445 if (prev) 446 return attempt_merge(q, prev, rq); 447 448 return 0; 449 } 450