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) || blk_discard_rq(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))
78 seg_size += bv->bv_len;
79 hw_seg_size += bv->bv_len;
84 if (nr_hw_segs == 1 &&
85 hw_seg_size > rq->bio->bi_hw_front_size)
86 rq->bio->bi_hw_front_size = hw_seg_size;
87 hw_seg_size = bv->bv_len;
92 seg_size = bv->bv_len;
96 if (nr_hw_segs == 1 &&
97 hw_seg_size > rq->bio->bi_hw_front_size)
98 rq->bio->bi_hw_front_size = hw_seg_size;
99 if (hw_seg_size > rq->biotail->bi_hw_back_size)
100 rq->biotail->bi_hw_back_size = hw_seg_size;
101 rq->nr_phys_segments = nr_phys_segs;
102 rq->nr_hw_segments = nr_hw_segs;
105 void blk_recount_segments(struct request_queue *q, struct bio *bio)
108 struct bio *nxt = bio->bi_next;
110 rq.bio = rq.biotail = bio;
112 blk_recalc_rq_segments(&rq);
114 bio->bi_phys_segments = rq.nr_phys_segments;
115 bio->bi_hw_segments = rq.nr_hw_segments;
116 bio->bi_flags |= (1 << BIO_SEG_VALID);
118 EXPORT_SYMBOL(blk_recount_segments);
120 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
123 if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
126 if (bio->bi_size + nxt->bi_size > q->max_segment_size)
129 if (!bio_has_data(bio))
132 if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
136 * bio and nxt are contiguous in memory; check if the queue allows
137 * these two to be merged into one
139 if (BIO_SEG_BOUNDARY(q, bio, nxt))
146 * map a request to scatterlist, return number of sg entries setup. Caller
147 * must make sure sg can hold rq->nr_phys_segments entries
149 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
150 struct scatterlist *sglist)
152 struct bio_vec *bvec, *bvprv;
153 struct req_iterator iter;
154 struct scatterlist *sg;
158 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
165 rq_for_each_segment(bvec, rq, iter) {
166 int nbytes = bvec->bv_len;
168 if (bvprv && cluster) {
169 if (sg->length + nbytes > q->max_segment_size)
172 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
174 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
177 sg->length += nbytes;
184 * If the driver previously mapped a shorter
185 * list, we could see a termination bit
186 * prematurely unless it fully inits the sg
187 * table on each mapping. We KNOW that there
188 * must be more entries here or the driver
189 * would be buggy, so force clear the
190 * termination bit to avoid doing a full
191 * sg_init_table() in drivers for each command.
193 sg->page_link &= ~0x02;
197 sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
201 } /* segments in rq */
204 if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
205 (rq->data_len & q->dma_pad_mask)) {
206 unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
208 sg->length += pad_len;
209 rq->extra_len += pad_len;
212 if (q->dma_drain_size && q->dma_drain_needed(rq)) {
213 if (rq->cmd_flags & REQ_RW)
214 memset(q->dma_drain_buffer, 0, q->dma_drain_size);
216 sg->page_link &= ~0x02;
218 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
220 ((unsigned long)q->dma_drain_buffer) &
223 rq->extra_len += q->dma_drain_size;
231 EXPORT_SYMBOL(blk_rq_map_sg);
233 static inline int ll_new_mergeable(struct request_queue *q,
237 int nr_phys_segs = bio_phys_segments(q, bio);
239 if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
240 req->cmd_flags |= REQ_NOMERGE;
241 if (req == q->last_merge)
242 q->last_merge = NULL;
247 * A hw segment is just getting larger, bump just the phys
250 req->nr_phys_segments += nr_phys_segs;
254 static inline int ll_new_hw_segment(struct request_queue *q,
258 int nr_hw_segs = bio_hw_segments(q, bio);
259 int nr_phys_segs = bio_phys_segments(q, bio);
261 if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
262 || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
263 req->cmd_flags |= REQ_NOMERGE;
264 if (req == q->last_merge)
265 q->last_merge = NULL;
270 * This will form the start of a new hw segment. Bump both
273 req->nr_hw_segments += nr_hw_segs;
274 req->nr_phys_segments += nr_phys_segs;
278 int ll_back_merge_fn(struct request_queue *q, struct request *req,
281 unsigned short max_sectors;
283 if (unlikely(blk_pc_request(req)))
284 max_sectors = q->max_hw_sectors;
286 max_sectors = q->max_sectors;
288 if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
289 req->cmd_flags |= REQ_NOMERGE;
290 if (req == q->last_merge)
291 q->last_merge = NULL;
294 if (!bio_flagged(req->biotail, BIO_SEG_VALID))
295 blk_recount_segments(q, req->biotail);
296 if (!bio_flagged(bio, BIO_SEG_VALID))
297 blk_recount_segments(q, bio);
299 return ll_new_hw_segment(q, req, bio);
302 int ll_front_merge_fn(struct request_queue *q, struct request *req,
305 unsigned short max_sectors;
307 if (unlikely(blk_pc_request(req)))
308 max_sectors = q->max_hw_sectors;
310 max_sectors = q->max_sectors;
313 if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
314 req->cmd_flags |= REQ_NOMERGE;
315 if (req == q->last_merge)
316 q->last_merge = NULL;
319 if (!bio_flagged(bio, BIO_SEG_VALID))
320 blk_recount_segments(q, bio);
321 if (!bio_flagged(req->bio, BIO_SEG_VALID))
322 blk_recount_segments(q, req->bio);
324 return ll_new_hw_segment(q, req, bio);
327 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
328 struct request *next)
330 int total_phys_segments;
331 int total_hw_segments;
334 * First check if the either of the requests are re-queued
335 * requests. Can't merge them if they are.
337 if (req->special || next->special)
341 * Will it become too large?
343 if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
346 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
347 if (blk_phys_contig_segment(q, req->biotail, next->bio))
348 total_phys_segments--;
350 if (total_phys_segments > q->max_phys_segments)
353 total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
355 if (total_hw_segments > q->max_hw_segments)
359 req->nr_phys_segments = total_phys_segments;
360 req->nr_hw_segments = total_hw_segments;
365 * Has to be called with the request spinlock acquired
367 static int attempt_merge(struct request_queue *q, struct request *req,
368 struct request *next)
370 if (!rq_mergeable(req) || !rq_mergeable(next))
376 if (req->sector + req->nr_sectors != next->sector)
379 if (rq_data_dir(req) != rq_data_dir(next)
380 || req->rq_disk != next->rq_disk
384 if (blk_integrity_rq(req) != blk_integrity_rq(next))
388 * If we are allowed to merge, then append bio list
389 * from next to rq and release next. merge_requests_fn
390 * will have updated segment counts, update sector
393 if (!ll_merge_requests_fn(q, req, next))
397 * At this point we have either done a back merge
398 * or front merge. We need the smaller start_time of
399 * the merged requests to be the current request
400 * for accounting purposes.
402 if (time_after(req->start_time, next->start_time))
403 req->start_time = next->start_time;
405 req->biotail->bi_next = next->bio;
406 req->biotail = next->biotail;
408 req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
410 elv_merge_requests(q, req, next);
413 struct hd_struct *part
414 = get_part(req->rq_disk, req->sector);
415 disk_round_stats(req->rq_disk);
416 req->rq_disk->in_flight--;
418 part_round_stats(part);
423 req->ioprio = ioprio_best(req->ioprio, next->ioprio);
425 __blk_put_request(q, next);
429 int attempt_back_merge(struct request_queue *q, struct request *rq)
431 struct request *next = elv_latter_request(q, rq);
434 return attempt_merge(q, rq, next);
439 int attempt_front_merge(struct request_queue *q, struct request *rq)
441 struct request *prev = elv_former_request(q, rq);
444 return attempt_merge(q, prev, rq);