Allow elevators to sort/merge discard requests
[linux-2.6.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) || blk_discard_rq(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 (bio->bi_size + nxt->bi_size > q->max_segment_size)
135                 return 0;
136
137         if (!bio_has_data(bio))
138                 return 1;
139
140         if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
141                 return 0;
142
143         /*
144          * bio and nxt are contiguous in memory; check if the queue allows
145          * these two to be merged into one
146          */
147         if (BIO_SEG_BOUNDARY(q, bio, nxt))
148                 return 1;
149
150         return 0;
151 }
152
153 static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio,
154                                  struct bio *nxt)
155 {
156         if (!bio_flagged(bio, BIO_SEG_VALID))
157                 blk_recount_segments(q, bio);
158         if (!bio_flagged(nxt, BIO_SEG_VALID))
159                 blk_recount_segments(q, nxt);
160         if (bio_has_data(bio) &&
161             (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
162              BIOVEC_VIRT_OVERSIZE(bio->bi_hw_back_size + nxt->bi_hw_front_size)))
163                 return 0;
164         if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size)
165                 return 0;
166
167         return 1;
168 }
169
170 /*
171  * map a request to scatterlist, return number of sg entries setup. Caller
172  * must make sure sg can hold rq->nr_phys_segments entries
173  */
174 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
175                   struct scatterlist *sglist)
176 {
177         struct bio_vec *bvec, *bvprv;
178         struct req_iterator iter;
179         struct scatterlist *sg;
180         int nsegs, cluster;
181
182         nsegs = 0;
183         cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
184
185         /*
186          * for each bio in rq
187          */
188         bvprv = NULL;
189         sg = NULL;
190         rq_for_each_segment(bvec, rq, iter) {
191                 int nbytes = bvec->bv_len;
192
193                 if (bvprv && cluster) {
194                         if (sg->length + nbytes > q->max_segment_size)
195                                 goto new_segment;
196
197                         if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
198                                 goto new_segment;
199                         if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
200                                 goto new_segment;
201
202                         sg->length += nbytes;
203                 } else {
204 new_segment:
205                         if (!sg)
206                                 sg = sglist;
207                         else {
208                                 /*
209                                  * If the driver previously mapped a shorter
210                                  * list, we could see a termination bit
211                                  * prematurely unless it fully inits the sg
212                                  * table on each mapping. We KNOW that there
213                                  * must be more entries here or the driver
214                                  * would be buggy, so force clear the
215                                  * termination bit to avoid doing a full
216                                  * sg_init_table() in drivers for each command.
217                                  */
218                                 sg->page_link &= ~0x02;
219                                 sg = sg_next(sg);
220                         }
221
222                         sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
223                         nsegs++;
224                 }
225                 bvprv = bvec;
226         } /* segments in rq */
227
228
229         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
230             (rq->data_len & q->dma_pad_mask)) {
231                 unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
232
233                 sg->length += pad_len;
234                 rq->extra_len += pad_len;
235         }
236
237         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
238                 if (rq->cmd_flags & REQ_RW)
239                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
240
241                 sg->page_link &= ~0x02;
242                 sg = sg_next(sg);
243                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
244                             q->dma_drain_size,
245                             ((unsigned long)q->dma_drain_buffer) &
246                             (PAGE_SIZE - 1));
247                 nsegs++;
248                 rq->extra_len += q->dma_drain_size;
249         }
250
251         if (sg)
252                 sg_mark_end(sg);
253
254         return nsegs;
255 }
256 EXPORT_SYMBOL(blk_rq_map_sg);
257
258 static inline int ll_new_mergeable(struct request_queue *q,
259                                    struct request *req,
260                                    struct bio *bio)
261 {
262         int nr_phys_segs = bio_phys_segments(q, bio);
263
264         if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
265                 req->cmd_flags |= REQ_NOMERGE;
266                 if (req == q->last_merge)
267                         q->last_merge = NULL;
268                 return 0;
269         }
270
271         /*
272          * A hw segment is just getting larger, bump just the phys
273          * counter.
274          */
275         req->nr_phys_segments += nr_phys_segs;
276         return 1;
277 }
278
279 static inline int ll_new_hw_segment(struct request_queue *q,
280                                     struct request *req,
281                                     struct bio *bio)
282 {
283         int nr_hw_segs = bio_hw_segments(q, bio);
284         int nr_phys_segs = bio_phys_segments(q, bio);
285
286         if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
287             || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
288                 req->cmd_flags |= REQ_NOMERGE;
289                 if (req == q->last_merge)
290                         q->last_merge = NULL;
291                 return 0;
292         }
293
294         /*
295          * This will form the start of a new hw segment.  Bump both
296          * counters.
297          */
298         req->nr_hw_segments += nr_hw_segs;
299         req->nr_phys_segments += nr_phys_segs;
300         return 1;
301 }
302
303 int ll_back_merge_fn(struct request_queue *q, struct request *req,
304                      struct bio *bio)
305 {
306         unsigned short max_sectors;
307         int len;
308
309         if (unlikely(blk_pc_request(req)))
310                 max_sectors = q->max_hw_sectors;
311         else
312                 max_sectors = q->max_sectors;
313
314         if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
315                 req->cmd_flags |= REQ_NOMERGE;
316                 if (req == q->last_merge)
317                         q->last_merge = NULL;
318                 return 0;
319         }
320         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
321                 blk_recount_segments(q, req->biotail);
322         if (!bio_flagged(bio, BIO_SEG_VALID))
323                 blk_recount_segments(q, bio);
324         len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
325         if (!bio_has_data(bio) || 
326             (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio))
327              && !BIOVEC_VIRT_OVERSIZE(len))) {
328                 int mergeable =  ll_new_mergeable(q, req, bio);
329
330                 if (mergeable) {
331                         if (req->nr_hw_segments == 1)
332                                 req->bio->bi_hw_front_size = len;
333                         if (bio->bi_hw_segments == 1)
334                                 bio->bi_hw_back_size = len;
335                 }
336                 return mergeable;
337         }
338
339         return ll_new_hw_segment(q, req, bio);
340 }
341
342 int ll_front_merge_fn(struct request_queue *q, struct request *req,
343                       struct bio *bio)
344 {
345         unsigned short max_sectors;
346         int len;
347
348         if (unlikely(blk_pc_request(req)))
349                 max_sectors = q->max_hw_sectors;
350         else
351                 max_sectors = q->max_sectors;
352
353
354         if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
355                 req->cmd_flags |= REQ_NOMERGE;
356                 if (req == q->last_merge)
357                         q->last_merge = NULL;
358                 return 0;
359         }
360         len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
361         if (!bio_flagged(bio, BIO_SEG_VALID))
362                 blk_recount_segments(q, bio);
363         if (!bio_flagged(req->bio, BIO_SEG_VALID))
364                 blk_recount_segments(q, req->bio);
365         if (!bio_has_data(bio) || 
366             (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
367              !BIOVEC_VIRT_OVERSIZE(len))) {
368                 int mergeable =  ll_new_mergeable(q, req, bio);
369
370                 if (mergeable) {
371                         if (bio->bi_hw_segments == 1)
372                                 bio->bi_hw_front_size = len;
373                         if (req->nr_hw_segments == 1)
374                                 req->biotail->bi_hw_back_size = len;
375                 }
376                 return mergeable;
377         }
378
379         return ll_new_hw_segment(q, req, bio);
380 }
381
382 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
383                                 struct request *next)
384 {
385         int total_phys_segments;
386         int total_hw_segments;
387
388         /*
389          * First check if the either of the requests are re-queued
390          * requests.  Can't merge them if they are.
391          */
392         if (req->special || next->special)
393                 return 0;
394
395         /*
396          * Will it become too large?
397          */
398         if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
399                 return 0;
400
401         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
402         if (blk_phys_contig_segment(q, req->biotail, next->bio))
403                 total_phys_segments--;
404
405         if (total_phys_segments > q->max_phys_segments)
406                 return 0;
407
408         total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
409         if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
410                 int len = req->biotail->bi_hw_back_size +
411                                 next->bio->bi_hw_front_size;
412                 /*
413                  * propagate the combined length to the end of the requests
414                  */
415                 if (req->nr_hw_segments == 1)
416                         req->bio->bi_hw_front_size = len;
417                 if (next->nr_hw_segments == 1)
418                         next->biotail->bi_hw_back_size = len;
419                 total_hw_segments--;
420         }
421
422         if (total_hw_segments > q->max_hw_segments)
423                 return 0;
424
425         /* Merge is OK... */
426         req->nr_phys_segments = total_phys_segments;
427         req->nr_hw_segments = total_hw_segments;
428         return 1;
429 }
430
431 /*
432  * Has to be called with the request spinlock acquired
433  */
434 static int attempt_merge(struct request_queue *q, struct request *req,
435                           struct request *next)
436 {
437         if (!rq_mergeable(req) || !rq_mergeable(next))
438                 return 0;
439
440         /*
441          * not contiguous
442          */
443         if (req->sector + req->nr_sectors != next->sector)
444                 return 0;
445
446         if (rq_data_dir(req) != rq_data_dir(next)
447             || req->rq_disk != next->rq_disk
448             || next->special)
449                 return 0;
450
451         if (blk_integrity_rq(req) != blk_integrity_rq(next))
452                 return 0;
453
454         /*
455          * If we are allowed to merge, then append bio list
456          * from next to rq and release next. merge_requests_fn
457          * will have updated segment counts, update sector
458          * counts here.
459          */
460         if (!ll_merge_requests_fn(q, req, next))
461                 return 0;
462
463         /*
464          * At this point we have either done a back merge
465          * or front merge. We need the smaller start_time of
466          * the merged requests to be the current request
467          * for accounting purposes.
468          */
469         if (time_after(req->start_time, next->start_time))
470                 req->start_time = next->start_time;
471
472         req->biotail->bi_next = next->bio;
473         req->biotail = next->biotail;
474
475         req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
476
477         elv_merge_requests(q, req, next);
478
479         if (req->rq_disk) {
480                 struct hd_struct *part
481                         = get_part(req->rq_disk, req->sector);
482                 disk_round_stats(req->rq_disk);
483                 req->rq_disk->in_flight--;
484                 if (part) {
485                         part_round_stats(part);
486                         part->in_flight--;
487                 }
488         }
489
490         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
491
492         __blk_put_request(q, next);
493         return 1;
494 }
495
496 int attempt_back_merge(struct request_queue *q, struct request *rq)
497 {
498         struct request *next = elv_latter_request(q, rq);
499
500         if (next)
501                 return attempt_merge(q, rq, next);
502
503         return 0;
504 }
505
506 int attempt_front_merge(struct request_queue *q, struct request *rq)
507 {
508         struct request *prev = elv_former_request(q, rq);
509
510         if (prev)
511                 return attempt_merge(q, prev, rq);
512
513         return 0;
514 }