blk-merge.c 10.3 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13
/*
 * Functions related to segment and merge handling
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/scatterlist.h>

#include "blk.h"

void blk_recalc_rq_sectors(struct request *rq, int nsect)
{
14
	if (blk_fs_request(rq) || blk_discard_rq(rq)) {
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
		rq->hard_sector += nsect;
		rq->hard_nr_sectors -= nsect;

		/*
		 * Move the I/O submission pointers ahead if required.
		 */
		if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
		    (rq->sector <= rq->hard_sector)) {
			rq->sector = rq->hard_sector;
			rq->nr_sectors = rq->hard_nr_sectors;
			rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
			rq->current_nr_sectors = rq->hard_cur_sectors;
			rq->buffer = bio_data(rq->bio);
		}

		/*
		 * if total number of sectors is less than the first segment
		 * size, something has gone terribly wrong
		 */
		if (rq->nr_sectors < rq->current_nr_sectors) {
35
			printk(KERN_ERR "blk: request botched\n");
36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
			rq->nr_sectors = rq->current_nr_sectors;
		}
	}
}

void blk_recalc_rq_segments(struct request *rq)
{
	int nr_phys_segs;
	unsigned int phys_size;
	struct bio_vec *bv, *bvprv = NULL;
	int seg_size;
	int cluster;
	struct req_iterator iter;
	int high, highprv = 1;
	struct request_queue *q = rq->q;

	if (!rq->bio)
		return;

55
	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
Mikulas Patocka's avatar
Mikulas Patocka committed
56 57
	seg_size = 0;
	phys_size = nr_phys_segs = 0;
58 59 60 61 62 63 64 65
	rq_for_each_segment(bv, rq, iter) {
		/*
		 * the trick here is making sure that a high page is never
		 * considered part of another segment, since that might
		 * change with the bounce page.
		 */
		high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
		if (high || highprv)
66
			goto new_segment;
67 68 69 70 71 72 73 74 75 76 77 78 79
		if (cluster) {
			if (seg_size + bv->bv_len > q->max_segment_size)
				goto new_segment;
			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
				goto new_segment;
			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
				goto new_segment;

			seg_size += bv->bv_len;
			bvprv = bv;
			continue;
		}
new_segment:
80 81 82
		if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
			rq->bio->bi_seg_front_size = seg_size;

83 84 85 86 87 88
		nr_phys_segs++;
		bvprv = bv;
		seg_size = bv->bv_len;
		highprv = high;
	}

89 90 91 92 93
	if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
		rq->bio->bi_seg_front_size = seg_size;
	if (seg_size > rq->biotail->bi_seg_back_size)
		rq->biotail->bi_seg_back_size = seg_size;

94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113
	rq->nr_phys_segments = nr_phys_segs;
}

void blk_recount_segments(struct request_queue *q, struct bio *bio)
{
	struct request rq;
	struct bio *nxt = bio->bi_next;
	rq.q = q;
	rq.bio = rq.biotail = bio;
	bio->bi_next = NULL;
	blk_recalc_rq_segments(&rq);
	bio->bi_next = nxt;
	bio->bi_phys_segments = rq.nr_phys_segments;
	bio->bi_flags |= (1 << BIO_SEG_VALID);
}
EXPORT_SYMBOL(blk_recount_segments);

static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
				   struct bio *nxt)
{
114
	if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
115 116
		return 0;

117 118
	if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
	    q->max_segment_size)
119 120
		return 0;

121 122 123 124 125 126
	if (!bio_has_data(bio))
		return 1;

	if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
		return 0;

127
	/*
128
	 * bio and nxt are contiguous in memory; check if the queue allows
129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
	 * these two to be merged into one
	 */
	if (BIO_SEG_BOUNDARY(q, bio, nxt))
		return 1;

	return 0;
}

/*
 * map a request to scatterlist, return number of sg entries setup. Caller
 * must make sure sg can hold rq->nr_phys_segments entries
 */
int blk_rq_map_sg(struct request_queue *q, struct request *rq,
		  struct scatterlist *sglist)
{
	struct bio_vec *bvec, *bvprv;
	struct req_iterator iter;
	struct scatterlist *sg;
	int nsegs, cluster;

	nsegs = 0;
150
	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194

	/*
	 * for each bio in rq
	 */
	bvprv = NULL;
	sg = NULL;
	rq_for_each_segment(bvec, rq, iter) {
		int nbytes = bvec->bv_len;

		if (bvprv && cluster) {
			if (sg->length + nbytes > q->max_segment_size)
				goto new_segment;

			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
				goto new_segment;
			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
				goto new_segment;

			sg->length += nbytes;
		} else {
new_segment:
			if (!sg)
				sg = sglist;
			else {
				/*
				 * If the driver previously mapped a shorter
				 * list, we could see a termination bit
				 * prematurely unless it fully inits the sg
				 * table on each mapping. We KNOW that there
				 * must be more entries here or the driver
				 * would be buggy, so force clear the
				 * termination bit to avoid doing a full
				 * sg_init_table() in drivers for each command.
				 */
				sg->page_link &= ~0x02;
				sg = sg_next(sg);
			}

			sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
			nsegs++;
		}
		bvprv = bvec;
	} /* segments in rq */

195 196 197 198 199 200 201 202 203

	if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
	    (rq->data_len & q->dma_pad_mask)) {
		unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;

		sg->length += pad_len;
		rq->extra_len += pad_len;
	}

204
	if (q->dma_drain_size && q->dma_drain_needed(rq)) {
205 206 207
		if (rq->cmd_flags & REQ_RW)
			memset(q->dma_drain_buffer, 0, q->dma_drain_size);

208 209 210 211 212 213 214
		sg->page_link &= ~0x02;
		sg = sg_next(sg);
		sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
			    q->dma_drain_size,
			    ((unsigned long)q->dma_drain_buffer) &
			    (PAGE_SIZE - 1));
		nsegs++;
215
		rq->extra_len += q->dma_drain_size;
216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251
	}

	if (sg)
		sg_mark_end(sg);

	return nsegs;
}
EXPORT_SYMBOL(blk_rq_map_sg);

static inline int ll_new_mergeable(struct request_queue *q,
				   struct request *req,
				   struct bio *bio)
{
	int nr_phys_segs = bio_phys_segments(q, bio);

	if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
		req->cmd_flags |= REQ_NOMERGE;
		if (req == q->last_merge)
			q->last_merge = NULL;
		return 0;
	}

	/*
	 * A hw segment is just getting larger, bump just the phys
	 * counter.
	 */
	req->nr_phys_segments += nr_phys_segs;
	return 1;
}

static inline int ll_new_hw_segment(struct request_queue *q,
				    struct request *req,
				    struct bio *bio)
{
	int nr_phys_segs = bio_phys_segments(q, bio);

Mikulas Patocka's avatar
Mikulas Patocka committed
252
	if (req->nr_phys_segments + nr_phys_segs > q->max_hw_segments
253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283
	    || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
		req->cmd_flags |= REQ_NOMERGE;
		if (req == q->last_merge)
			q->last_merge = NULL;
		return 0;
	}

	/*
	 * This will form the start of a new hw segment.  Bump both
	 * counters.
	 */
	req->nr_phys_segments += nr_phys_segs;
	return 1;
}

int ll_back_merge_fn(struct request_queue *q, struct request *req,
		     struct bio *bio)
{
	unsigned short max_sectors;

	if (unlikely(blk_pc_request(req)))
		max_sectors = q->max_hw_sectors;
	else
		max_sectors = q->max_sectors;

	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
		req->cmd_flags |= REQ_NOMERGE;
		if (req == q->last_merge)
			q->last_merge = NULL;
		return 0;
	}
284
	if (!bio_flagged(req->biotail, BIO_SEG_VALID))
285
		blk_recount_segments(q, req->biotail);
286
	if (!bio_flagged(bio, BIO_SEG_VALID))
287 288 289 290 291
		blk_recount_segments(q, bio);

	return ll_new_hw_segment(q, req, bio);
}

292
int ll_front_merge_fn(struct request_queue *q, struct request *req,
293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308
		      struct bio *bio)
{
	unsigned short max_sectors;

	if (unlikely(blk_pc_request(req)))
		max_sectors = q->max_hw_sectors;
	else
		max_sectors = q->max_sectors;


	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
		req->cmd_flags |= REQ_NOMERGE;
		if (req == q->last_merge)
			q->last_merge = NULL;
		return 0;
	}
309
	if (!bio_flagged(bio, BIO_SEG_VALID))
310
		blk_recount_segments(q, bio);
311
	if (!bio_flagged(req->bio, BIO_SEG_VALID))
312 313 314 315 316 317 318 319 320
		blk_recount_segments(q, req->bio);

	return ll_new_hw_segment(q, req, bio);
}

static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
				struct request *next)
{
	int total_phys_segments;
321 322
	unsigned int seg_size =
		req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
323 324 325 326 327 328 329 330 331 332 333 334 335 336 337

	/*
	 * First check if the either of the requests are re-queued
	 * requests.  Can't merge them if they are.
	 */
	if (req->special || next->special)
		return 0;

	/*
	 * Will it become too large?
	 */
	if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
		return 0;

	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
338 339 340 341 342
	if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
		if (req->nr_phys_segments == 1)
			req->bio->bi_seg_front_size = seg_size;
		if (next->nr_phys_segments == 1)
			next->biotail->bi_seg_back_size = seg_size;
343
		total_phys_segments--;
344
	}
345 346 347 348

	if (total_phys_segments > q->max_phys_segments)
		return 0;

Mikulas Patocka's avatar
Mikulas Patocka committed
349
	if (total_phys_segments > q->max_hw_segments)
350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376
		return 0;

	/* Merge is OK... */
	req->nr_phys_segments = total_phys_segments;
	return 1;
}

/*
 * Has to be called with the request spinlock acquired
 */
static int attempt_merge(struct request_queue *q, struct request *req,
			  struct request *next)
{
	if (!rq_mergeable(req) || !rq_mergeable(next))
		return 0;

	/*
	 * not contiguous
	 */
	if (req->sector + req->nr_sectors != next->sector)
		return 0;

	if (rq_data_dir(req) != rq_data_dir(next)
	    || req->rq_disk != next->rq_disk
	    || next->special)
		return 0;

377 378 379
	if (blk_integrity_rq(req) != blk_integrity_rq(next))
		return 0;

380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405
	/*
	 * If we are allowed to merge, then append bio list
	 * from next to rq and release next. merge_requests_fn
	 * will have updated segment counts, update sector
	 * counts here.
	 */
	if (!ll_merge_requests_fn(q, req, next))
		return 0;

	/*
	 * At this point we have either done a back merge
	 * or front merge. We need the smaller start_time of
	 * the merged requests to be the current request
	 * for accounting purposes.
	 */
	if (time_after(req->start_time, next->start_time))
		req->start_time = next->start_time;

	req->biotail->bi_next = next->bio;
	req->biotail = next->biotail;

	req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;

	elv_merge_requests(q, req, next);

	if (req->rq_disk) {
406
		struct hd_struct *part;
Tejun Heo's avatar
Tejun Heo committed
407
		int cpu;
408

409
		cpu = part_stat_lock();
410
		part = disk_map_sector_rcu(req->rq_disk, req->sector);
Tejun Heo's avatar
Tejun Heo committed
411

412 413
		part_round_stats(cpu, part);
		part_dec_in_flight(part);
414

415
		part_stat_unlock();
416 417 418
	}

	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
419 420
	if (blk_rq_cpu_valid(next))
		req->cpu = next->cpu;
421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444

	__blk_put_request(q, next);
	return 1;
}

int attempt_back_merge(struct request_queue *q, struct request *rq)
{
	struct request *next = elv_latter_request(q, rq);

	if (next)
		return attempt_merge(q, rq, next);

	return 0;
}

int attempt_front_merge(struct request_queue *q, struct request *rq)
{
	struct request *prev = elv_former_request(q, rq);

	if (prev)
		return attempt_merge(q, prev, rq);

	return 0;
}