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 /* don't merge requests of different failfast settings */ 354 if (blk_failfast_dev(req) != blk_failfast_dev(next) || 355 blk_failfast_transport(req) != blk_failfast_transport(next) || 356 blk_failfast_driver(req) != blk_failfast_driver(next)) 357 return 0; 358 359 /* 360 * If we are allowed to merge, then append bio list 361 * from next to rq and release next. merge_requests_fn 362 * will have updated segment counts, update sector 363 * counts here. 364 */ 365 if (!ll_merge_requests_fn(q, req, next)) 366 return 0; 367 368 /* 369 * At this point we have either done a back merge 370 * or front merge. We need the smaller start_time of 371 * the merged requests to be the current request 372 * for accounting purposes. 373 */ 374 if (time_after(req->start_time, next->start_time)) 375 req->start_time = next->start_time; 376 377 req->biotail->bi_next = next->bio; 378 req->biotail = next->biotail; 379 380 req->__data_len += blk_rq_bytes(next); 381 382 elv_merge_requests(q, req, next); 383 384 /* 385 * 'next' is going away, so update stats accordingly 386 */ 387 blk_account_io_merge(next); 388 389 req->ioprio = ioprio_best(req->ioprio, next->ioprio); 390 if (blk_rq_cpu_valid(next)) 391 req->cpu = next->cpu; 392 393 /* owner-ship of bio passed from next to req */ 394 next->bio = NULL; 395 __blk_put_request(q, next); 396 return 1; 397 } 398 399 int attempt_back_merge(struct request_queue *q, struct request *rq) 400 { 401 struct request *next = elv_latter_request(q, rq); 402 403 if (next) 404 return attempt_merge(q, rq, next); 405 406 return 0; 407 } 408 409 int attempt_front_merge(struct request_queue *q, struct request *rq) 410 { 411 struct request *prev = elv_former_request(q, rq); 412 413 if (prev) 414 return attempt_merge(q, prev, rq); 415 416 return 0; 417 } 418