2 * Functions related to segment and merge handling
4 #include <linux/kernel.h>
5 #include <linux/module.h>
7 #include <linux/blkdev.h>
8 #include <linux/scatterlist.h>
12 void blk_recalc_rq_sectors(struct request *rq, int nsect)
14 if (blk_fs_request(rq)) {
15 rq->hard_sector += nsect;
16 rq->hard_nr_sectors -= nsect;
19 * Move the I/O submission pointers ahead if required.
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);
31 * if total number of sectors is less than the first segment
32 * size, something has gone terribly wrong
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;
41 void blk_recalc_rq_segments(struct request *rq)
45 unsigned int phys_size;
47 struct bio_vec *bv, *bvprv = NULL;
51 struct req_iterator iter;
52 int high, highprv = 1;
53 struct request_queue *q = rq->q;
58 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
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) {
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.
67 high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
71 if (seg_size + bv->bv_len > q->max_segment_size)
73 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
75 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
77 if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
80 seg_size += bv->bv_len;
81 hw_seg_size += bv->bv_len;
86 if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
87 !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
88 hw_seg_size += bv->bv_len;
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;
100 seg_size = bv->bv_len;
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;
113 void blk_recount_segments(struct request_queue *q, struct bio *bio)
116 struct bio *nxt = bio->bi_next;
118 rq.bio = rq.biotail = bio;
120 blk_recalc_rq_segments(&rq);
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);
126 EXPORT_SYMBOL(blk_recount_segments);
128 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
131 if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
134 if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
136 if (bio->bi_size + nxt->bi_size > q->max_segment_size)
140 * bio and nxt are contigous in memory, check if the queue allows
141 * these two to be merged into one
143 if (BIO_SEG_BOUNDARY(q, bio, nxt))
149 static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio,
152 if (!bio_flagged(bio, BIO_SEG_VALID))
153 blk_recount_segments(q, bio);
154 if (!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))
159 if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size)
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
169 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
170 struct scatterlist *sglist)
172 struct bio_vec *bvec, *bvprv;
173 struct req_iterator iter;
174 struct scatterlist *sg;
178 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
185 rq_for_each_segment(bvec, rq, iter) {
186 int nbytes = bvec->bv_len;
188 if (bvprv && cluster) {
189 if (sg->length + nbytes > q->max_segment_size)
192 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
194 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
197 sg->length += nbytes;
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.
213 sg->page_link &= ~0x02;
217 sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
221 } /* segments in rq */
224 if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
225 (rq->data_len & q->dma_pad_mask)) {
226 unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
228 sg->length += pad_len;
229 rq->extra_len += pad_len;
232 if (q->dma_drain_size && q->dma_drain_needed(rq)) {
233 if (rq->cmd_flags & REQ_RW)
234 memset(q->dma_drain_buffer, 0, q->dma_drain_size);
236 sg->page_link &= ~0x02;
238 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
240 ((unsigned long)q->dma_drain_buffer) &
243 rq->extra_len += q->dma_drain_size;
251 EXPORT_SYMBOL(blk_rq_map_sg);
253 static inline int ll_new_mergeable(struct request_queue *q,
257 int nr_phys_segs = bio_phys_segments(q, bio);
259 if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
260 req->cmd_flags |= REQ_NOMERGE;
261 if (req == q->last_merge)
262 q->last_merge = NULL;
267 * A hw segment is just getting larger, bump just the phys
270 req->nr_phys_segments += nr_phys_segs;
274 static inline int ll_new_hw_segment(struct request_queue *q,
278 int nr_hw_segs = bio_hw_segments(q, bio);
279 int nr_phys_segs = bio_phys_segments(q, bio);
281 if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
282 || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
283 req->cmd_flags |= REQ_NOMERGE;
284 if (req == q->last_merge)
285 q->last_merge = NULL;
290 * This will form the start of a new hw segment. Bump both
293 req->nr_hw_segments += nr_hw_segs;
294 req->nr_phys_segments += nr_phys_segs;
298 int ll_back_merge_fn(struct request_queue *q, struct request *req,
301 unsigned short max_sectors;
304 if (unlikely(blk_pc_request(req)))
305 max_sectors = q->max_hw_sectors;
307 max_sectors = q->max_sectors;
309 if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
310 req->cmd_flags |= REQ_NOMERGE;
311 if (req == q->last_merge)
312 q->last_merge = NULL;
315 if (!bio_flagged(req->biotail, BIO_SEG_VALID))
316 blk_recount_segments(q, req->biotail);
317 if (!bio_flagged(bio, BIO_SEG_VALID))
318 blk_recount_segments(q, bio);
319 len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
320 if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio))
321 && !BIOVEC_VIRT_OVERSIZE(len)) {
322 int mergeable = ll_new_mergeable(q, req, bio);
325 if (req->nr_hw_segments == 1)
326 req->bio->bi_hw_front_size = len;
327 if (bio->bi_hw_segments == 1)
328 bio->bi_hw_back_size = len;
333 return ll_new_hw_segment(q, req, bio);
336 int ll_front_merge_fn(struct request_queue *q, struct request *req,
339 unsigned short max_sectors;
342 if (unlikely(blk_pc_request(req)))
343 max_sectors = q->max_hw_sectors;
345 max_sectors = q->max_sectors;
348 if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
349 req->cmd_flags |= REQ_NOMERGE;
350 if (req == q->last_merge)
351 q->last_merge = NULL;
354 len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
355 if (!bio_flagged(bio, BIO_SEG_VALID))
356 blk_recount_segments(q, bio);
357 if (!bio_flagged(req->bio, BIO_SEG_VALID))
358 blk_recount_segments(q, req->bio);
359 if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
360 !BIOVEC_VIRT_OVERSIZE(len)) {
361 int mergeable = ll_new_mergeable(q, req, bio);
364 if (bio->bi_hw_segments == 1)
365 bio->bi_hw_front_size = len;
366 if (req->nr_hw_segments == 1)
367 req->biotail->bi_hw_back_size = len;
372 return ll_new_hw_segment(q, req, bio);
375 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
376 struct request *next)
378 int total_phys_segments;
379 int total_hw_segments;
382 * First check if the either of the requests are re-queued
383 * requests. Can't merge them if they are.
385 if (req->special || next->special)
389 * Will it become too large?
391 if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
394 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
395 if (blk_phys_contig_segment(q, req->biotail, next->bio))
396 total_phys_segments--;
398 if (total_phys_segments > q->max_phys_segments)
401 total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
402 if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
403 int len = req->biotail->bi_hw_back_size +
404 next->bio->bi_hw_front_size;
406 * propagate the combined length to the end of the requests
408 if (req->nr_hw_segments == 1)
409 req->bio->bi_hw_front_size = len;
410 if (next->nr_hw_segments == 1)
411 next->biotail->bi_hw_back_size = len;
415 if (total_hw_segments > q->max_hw_segments)
419 req->nr_phys_segments = total_phys_segments;
420 req->nr_hw_segments = total_hw_segments;
425 * Has to be called with the request spinlock acquired
427 static int attempt_merge(struct request_queue *q, struct request *req,
428 struct request *next)
430 if (!rq_mergeable(req) || !rq_mergeable(next))
436 if (req->sector + req->nr_sectors != next->sector)
439 if (rq_data_dir(req) != rq_data_dir(next)
440 || req->rq_disk != next->rq_disk
445 * If we are allowed to merge, then append bio list
446 * from next to rq and release next. merge_requests_fn
447 * will have updated segment counts, update sector
450 if (!ll_merge_requests_fn(q, req, next))
454 * At this point we have either done a back merge
455 * or front merge. We need the smaller start_time of
456 * the merged requests to be the current request
457 * for accounting purposes.
459 if (time_after(req->start_time, next->start_time))
460 req->start_time = next->start_time;
462 req->biotail->bi_next = next->bio;
463 req->biotail = next->biotail;
465 req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
467 elv_merge_requests(q, req, next);
470 struct hd_struct *part
471 = get_part(req->rq_disk, req->sector);
472 disk_round_stats(req->rq_disk);
473 req->rq_disk->in_flight--;
475 part_round_stats(part);
480 req->ioprio = ioprio_best(req->ioprio, next->ioprio);
482 __blk_put_request(q, next);
486 int attempt_back_merge(struct request_queue *q, struct request *rq)
488 struct request *next = elv_latter_request(q, rq);
491 return attempt_merge(q, rq, next);
496 int attempt_front_merge(struct request_queue *q, struct request *rq)
498 struct request *prev = elv_former_request(q, rq);
501 return attempt_merge(q, prev, rq);