block: get rid of likely/unlikely predictions in merge logic
[linux-3.10.git] / block / blk-merge.c
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 void blk_recalc_rq_sectors(struct request *rq, int nsect)
13 {
14         if (blk_fs_request(rq)) {
15                 rq->hard_sector += nsect;
16                 rq->hard_nr_sectors -= nsect;
17
18                 /*
19                  * Move the I/O submission pointers ahead if required.
20                  */
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);
28                 }
29
30                 /*
31                  * if total number of sectors is less than the first segment
32                  * size, something has gone terribly wrong
33                  */
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;
37                 }
38         }
39 }
40
41 void blk_recalc_rq_segments(struct request *rq)
42 {
43         int nr_phys_segs;
44         int nr_hw_segs;
45         unsigned int phys_size;
46         unsigned int hw_size;
47         struct bio_vec *bv, *bvprv = NULL;
48         int seg_size;
49         int hw_seg_size;
50         int cluster;
51         struct req_iterator iter;
52         int high, highprv = 1;
53         struct request_queue *q = rq->q;
54
55         if (!rq->bio)
56                 return;
57
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) {
62                 /*
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.
66                  */
67                 high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
68                 if (high || highprv)
69                         goto new_hw_segment;
70                 if (cluster) {
71                         if (seg_size + bv->bv_len > q->max_segment_size)
72                                 goto new_segment;
73                         if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
74                                 goto new_segment;
75                         if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
76                                 goto new_segment;
77                         if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
78                                 goto new_hw_segment;
79
80                         seg_size += bv->bv_len;
81                         hw_seg_size += bv->bv_len;
82                         bvprv = bv;
83                         continue;
84                 }
85 new_segment:
86                 if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
87                     !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
88                         hw_seg_size += bv->bv_len;
89                 else {
90 new_hw_segment:
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;
95                         nr_hw_segs++;
96                 }
97
98                 nr_phys_segs++;
99                 bvprv = bv;
100                 seg_size = bv->bv_len;
101                 highprv = high;
102         }
103
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;
111 }
112
113 void blk_recount_segments(struct request_queue *q, struct bio *bio)
114 {
115         struct request rq;
116         struct bio *nxt = bio->bi_next;
117         rq.q = q;
118         rq.bio = rq.biotail = bio;
119         bio->bi_next = NULL;
120         blk_recalc_rq_segments(&rq);
121         bio->bi_next = nxt;
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);
125 }
126 EXPORT_SYMBOL(blk_recount_segments);
127
128 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
129                                    struct bio *nxt)
130 {
131         if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
132                 return 0;
133
134         if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
135                 return 0;
136         if (bio->bi_size + nxt->bi_size > q->max_segment_size)
137                 return 0;
138
139         /*
140          * bio and nxt are contigous in memory, check if the queue allows
141          * these two to be merged into one
142          */
143         if (BIO_SEG_BOUNDARY(q, bio, nxt))
144                 return 1;
145
146         return 0;
147 }
148
149 static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio,
150                                  struct bio *nxt)
151 {
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))
158                 return 0;
159         if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size)
160                 return 0;
161
162         return 1;
163 }
164
165 /*
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
168  */
169 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
170                   struct scatterlist *sglist)
171 {
172         struct bio_vec *bvec, *bvprv;
173         struct req_iterator iter;
174         struct scatterlist *sg;
175         int nsegs, cluster;
176
177         nsegs = 0;
178         cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
179
180         /*
181          * for each bio in rq
182          */
183         bvprv = NULL;
184         sg = NULL;
185         rq_for_each_segment(bvec, rq, iter) {
186                 int nbytes = bvec->bv_len;
187
188                 if (bvprv && cluster) {
189                         if (sg->length + nbytes > q->max_segment_size)
190                                 goto new_segment;
191
192                         if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
193                                 goto new_segment;
194                         if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
195                                 goto new_segment;
196
197                         sg->length += nbytes;
198                 } else {
199 new_segment:
200                         if (!sg)
201                                 sg = sglist;
202                         else {
203                                 /*
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.
212                                  */
213                                 sg->page_link &= ~0x02;
214                                 sg = sg_next(sg);
215                         }
216
217                         sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
218                         nsegs++;
219                 }
220                 bvprv = bvec;
221         } /* segments in rq */
222
223
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;
227
228                 sg->length += pad_len;
229                 rq->extra_len += pad_len;
230         }
231
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);
235
236                 sg->page_link &= ~0x02;
237                 sg = sg_next(sg);
238                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
239                             q->dma_drain_size,
240                             ((unsigned long)q->dma_drain_buffer) &
241                             (PAGE_SIZE - 1));
242                 nsegs++;
243                 rq->extra_len += q->dma_drain_size;
244         }
245
246         if (sg)
247                 sg_mark_end(sg);
248
249         return nsegs;
250 }
251 EXPORT_SYMBOL(blk_rq_map_sg);
252
253 static inline int ll_new_mergeable(struct request_queue *q,
254                                    struct request *req,
255                                    struct bio *bio)
256 {
257         int nr_phys_segs = bio_phys_segments(q, bio);
258
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;
263                 return 0;
264         }
265
266         /*
267          * A hw segment is just getting larger, bump just the phys
268          * counter.
269          */
270         req->nr_phys_segments += nr_phys_segs;
271         return 1;
272 }
273
274 static inline int ll_new_hw_segment(struct request_queue *q,
275                                     struct request *req,
276                                     struct bio *bio)
277 {
278         int nr_hw_segs = bio_hw_segments(q, bio);
279         int nr_phys_segs = bio_phys_segments(q, bio);
280
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;
286                 return 0;
287         }
288
289         /*
290          * This will form the start of a new hw segment.  Bump both
291          * counters.
292          */
293         req->nr_hw_segments += nr_hw_segs;
294         req->nr_phys_segments += nr_phys_segs;
295         return 1;
296 }
297
298 int ll_back_merge_fn(struct request_queue *q, struct request *req,
299                      struct bio *bio)
300 {
301         unsigned short max_sectors;
302         int len;
303
304         if (unlikely(blk_pc_request(req)))
305                 max_sectors = q->max_hw_sectors;
306         else
307                 max_sectors = q->max_sectors;
308
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;
313                 return 0;
314         }
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);
323
324                 if (mergeable) {
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;
329                 }
330                 return mergeable;
331         }
332
333         return ll_new_hw_segment(q, req, bio);
334 }
335
336 int ll_front_merge_fn(struct request_queue *q, struct request *req,
337                       struct bio *bio)
338 {
339         unsigned short max_sectors;
340         int len;
341
342         if (unlikely(blk_pc_request(req)))
343                 max_sectors = q->max_hw_sectors;
344         else
345                 max_sectors = q->max_sectors;
346
347
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;
352                 return 0;
353         }
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);
362
363                 if (mergeable) {
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;
368                 }
369                 return mergeable;
370         }
371
372         return ll_new_hw_segment(q, req, bio);
373 }
374
375 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
376                                 struct request *next)
377 {
378         int total_phys_segments;
379         int total_hw_segments;
380
381         /*
382          * First check if the either of the requests are re-queued
383          * requests.  Can't merge them if they are.
384          */
385         if (req->special || next->special)
386                 return 0;
387
388         /*
389          * Will it become too large?
390          */
391         if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
392                 return 0;
393
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--;
397
398         if (total_phys_segments > q->max_phys_segments)
399                 return 0;
400
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;
405                 /*
406                  * propagate the combined length to the end of the requests
407                  */
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;
412                 total_hw_segments--;
413         }
414
415         if (total_hw_segments > q->max_hw_segments)
416                 return 0;
417
418         /* Merge is OK... */
419         req->nr_phys_segments = total_phys_segments;
420         req->nr_hw_segments = total_hw_segments;
421         return 1;
422 }
423
424 /*
425  * Has to be called with the request spinlock acquired
426  */
427 static int attempt_merge(struct request_queue *q, struct request *req,
428                           struct request *next)
429 {
430         if (!rq_mergeable(req) || !rq_mergeable(next))
431                 return 0;
432
433         /*
434          * not contiguous
435          */
436         if (req->sector + req->nr_sectors != next->sector)
437                 return 0;
438
439         if (rq_data_dir(req) != rq_data_dir(next)
440             || req->rq_disk != next->rq_disk
441             || next->special)
442                 return 0;
443
444         /*
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
448          * counts here.
449          */
450         if (!ll_merge_requests_fn(q, req, next))
451                 return 0;
452
453         /*
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.
458          */
459         if (time_after(req->start_time, next->start_time))
460                 req->start_time = next->start_time;
461
462         req->biotail->bi_next = next->bio;
463         req->biotail = next->biotail;
464
465         req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
466
467         elv_merge_requests(q, req, next);
468
469         if (req->rq_disk) {
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--;
474                 if (part) {
475                         part_round_stats(part);
476                         part->in_flight--;
477                 }
478         }
479
480         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
481
482         __blk_put_request(q, next);
483         return 1;
484 }
485
486 int attempt_back_merge(struct request_queue *q, struct request *rq)
487 {
488         struct request *next = elv_latter_request(q, rq);
489
490         if (next)
491                 return attempt_merge(q, rq, next);
492
493         return 0;
494 }
495
496 int attempt_front_merge(struct request_queue *q, struct request *rq)
497 {
498         struct request *prev = elv_former_request(q, rq);
499
500         if (prev)
501                 return attempt_merge(q, prev, rq);
502
503         return 0;
504 }