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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 | static unsigned int __blk_recalc_rq_segments(struct request_queue *q, |
13 | struct bio *bio) |
14 | { |
15 | unsigned int phys_size; |
16 | struct bio_vec *bv, *bvprv = NULL; |
17 | int cluster, i, high, highprv = 1; |
18 | unsigned int seg_size, nr_phys_segs; |
19 | struct bio *fbio, *bbio; |
20 | |
21 | if (!bio) |
22 | return 0; |
23 | |
24 | fbio = bio; |
25 | cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); |
26 | seg_size = 0; |
27 | phys_size = nr_phys_segs = 0; |
28 | for_each_bio(bio) { |
29 | bio_for_each_segment(bv, bio, i) { |
30 | /* |
31 | * the trick here is making sure that a high page is |
32 | * never considered part of another segment, since that |
33 | * might change with the bounce page. |
34 | */ |
35 | high = page_to_pfn(bv->bv_page) > queue_bounce_pfn(q); |
36 | if (high || highprv) |
37 | goto new_segment; |
38 | if (cluster) { |
39 | if (seg_size + bv->bv_len |
40 | > queue_max_segment_size(q)) |
41 | goto new_segment; |
42 | if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv)) |
43 | goto new_segment; |
44 | if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv)) |
45 | goto new_segment; |
46 | |
47 | seg_size += bv->bv_len; |
48 | bvprv = bv; |
49 | continue; |
50 | } |
51 | new_segment: |
52 | if (nr_phys_segs == 1 && seg_size > |
53 | fbio->bi_seg_front_size) |
54 | fbio->bi_seg_front_size = seg_size; |
55 | |
56 | nr_phys_segs++; |
57 | bvprv = bv; |
58 | seg_size = bv->bv_len; |
59 | highprv = high; |
60 | } |
61 | bbio = bio; |
62 | } |
63 | |
64 | if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size) |
65 | fbio->bi_seg_front_size = seg_size; |
66 | if (seg_size > bbio->bi_seg_back_size) |
67 | bbio->bi_seg_back_size = seg_size; |
68 | |
69 | return nr_phys_segs; |
70 | } |
71 | |
72 | void blk_recalc_rq_segments(struct request *rq) |
73 | { |
74 | rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio); |
75 | } |
76 | |
77 | void blk_recount_segments(struct request_queue *q, struct bio *bio) |
78 | { |
79 | struct bio *nxt = bio->bi_next; |
80 | |
81 | bio->bi_next = NULL; |
82 | bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio); |
83 | bio->bi_next = nxt; |
84 | bio->bi_flags |= (1 << BIO_SEG_VALID); |
85 | } |
86 | EXPORT_SYMBOL(blk_recount_segments); |
87 | |
88 | static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio, |
89 | struct bio *nxt) |
90 | { |
91 | if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags)) |
92 | return 0; |
93 | |
94 | if (bio->bi_seg_back_size + nxt->bi_seg_front_size > |
95 | queue_max_segment_size(q)) |
96 | return 0; |
97 | |
98 | if (!bio_has_data(bio)) |
99 | return 1; |
100 | |
101 | if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt))) |
102 | return 0; |
103 | |
104 | /* |
105 | * bio and nxt are contiguous in memory; check if the queue allows |
106 | * these two to be merged into one |
107 | */ |
108 | if (BIO_SEG_BOUNDARY(q, bio, nxt)) |
109 | return 1; |
110 | |
111 | return 0; |
112 | } |
113 | |
114 | /* |
115 | * map a request to scatterlist, return number of sg entries setup. Caller |
116 | * must make sure sg can hold rq->nr_phys_segments entries |
117 | */ |
118 | int blk_rq_map_sg(struct request_queue *q, struct request *rq, |
119 | struct scatterlist *sglist) |
120 | { |
121 | struct bio_vec *bvec, *bvprv; |
122 | struct req_iterator iter; |
123 | struct scatterlist *sg; |
124 | int nsegs, cluster; |
125 | |
126 | nsegs = 0; |
127 | cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); |
128 | |
129 | /* |
130 | * for each bio in rq |
131 | */ |
132 | bvprv = NULL; |
133 | sg = NULL; |
134 | rq_for_each_segment(bvec, rq, iter) { |
135 | int nbytes = bvec->bv_len; |
136 | |
137 | if (bvprv && cluster) { |
138 | if (sg->length + nbytes > queue_max_segment_size(q)) |
139 | goto new_segment; |
140 | |
141 | if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec)) |
142 | goto new_segment; |
143 | if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec)) |
144 | goto new_segment; |
145 | |
146 | sg->length += nbytes; |
147 | } else { |
148 | new_segment: |
149 | if (!sg) |
150 | sg = sglist; |
151 | else { |
152 | /* |
153 | * If the driver previously mapped a shorter |
154 | * list, we could see a termination bit |
155 | * prematurely unless it fully inits the sg |
156 | * table on each mapping. We KNOW that there |
157 | * must be more entries here or the driver |
158 | * would be buggy, so force clear the |
159 | * termination bit to avoid doing a full |
160 | * sg_init_table() in drivers for each command. |
161 | */ |
162 | sg->page_link &= ~0x02; |
163 | sg = sg_next(sg); |
164 | } |
165 | |
166 | sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset); |
167 | nsegs++; |
168 | } |
169 | bvprv = bvec; |
170 | } /* segments in rq */ |
171 | |
172 | |
173 | if (unlikely(rq->cmd_flags & REQ_COPY_USER) && |
174 | (blk_rq_bytes(rq) & q->dma_pad_mask)) { |
175 | unsigned int pad_len = |
176 | (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1; |
177 | |
178 | sg->length += pad_len; |
179 | rq->extra_len += pad_len; |
180 | } |
181 | |
182 | if (q->dma_drain_size && q->dma_drain_needed(rq)) { |
183 | if (rq->cmd_flags & REQ_RW) |
184 | memset(q->dma_drain_buffer, 0, q->dma_drain_size); |
185 | |
186 | sg->page_link &= ~0x02; |
187 | sg = sg_next(sg); |
188 | sg_set_page(sg, virt_to_page(q->dma_drain_buffer), |
189 | q->dma_drain_size, |
190 | ((unsigned long)q->dma_drain_buffer) & |
191 | (PAGE_SIZE - 1)); |
192 | nsegs++; |
193 | rq->extra_len += q->dma_drain_size; |
194 | } |
195 | |
196 | if (sg) |
197 | sg_mark_end(sg); |
198 | |
199 | return nsegs; |
200 | } |
201 | EXPORT_SYMBOL(blk_rq_map_sg); |
202 | |
203 | static inline int ll_new_hw_segment(struct request_queue *q, |
204 | struct request *req, |
205 | struct bio *bio) |
206 | { |
207 | int nr_phys_segs = bio_phys_segments(q, bio); |
208 | |
209 | if (req->nr_phys_segments + nr_phys_segs > queue_max_hw_segments(q) || |
210 | req->nr_phys_segments + nr_phys_segs > queue_max_phys_segments(q)) { |
211 | req->cmd_flags |= REQ_NOMERGE; |
212 | if (req == q->last_merge) |
213 | q->last_merge = NULL; |
214 | return 0; |
215 | } |
216 | |
217 | /* |
218 | * This will form the start of a new hw segment. Bump both |
219 | * counters. |
220 | */ |
221 | req->nr_phys_segments += nr_phys_segs; |
222 | return 1; |
223 | } |
224 | |
225 | int ll_back_merge_fn(struct request_queue *q, struct request *req, |
226 | struct bio *bio) |
227 | { |
228 | unsigned short max_sectors; |
229 | |
230 | if (unlikely(blk_pc_request(req))) |
231 | max_sectors = queue_max_hw_sectors(q); |
232 | else |
233 | max_sectors = queue_max_sectors(q); |
234 | |
235 | if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) { |
236 | req->cmd_flags |= REQ_NOMERGE; |
237 | if (req == q->last_merge) |
238 | q->last_merge = NULL; |
239 | return 0; |
240 | } |
241 | if (!bio_flagged(req->biotail, BIO_SEG_VALID)) |
242 | blk_recount_segments(q, req->biotail); |
243 | if (!bio_flagged(bio, BIO_SEG_VALID)) |
244 | blk_recount_segments(q, bio); |
245 | |
246 | return ll_new_hw_segment(q, req, bio); |
247 | } |
248 | |
249 | int ll_front_merge_fn(struct request_queue *q, struct request *req, |
250 | struct bio *bio) |
251 | { |
252 | unsigned short max_sectors; |
253 | |
254 | if (unlikely(blk_pc_request(req))) |
255 | max_sectors = queue_max_hw_sectors(q); |
256 | else |
257 | max_sectors = queue_max_sectors(q); |
258 | |
259 | |
260 | if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) { |
261 | req->cmd_flags |= REQ_NOMERGE; |
262 | if (req == q->last_merge) |
263 | q->last_merge = NULL; |
264 | return 0; |
265 | } |
266 | if (!bio_flagged(bio, BIO_SEG_VALID)) |
267 | blk_recount_segments(q, bio); |
268 | if (!bio_flagged(req->bio, BIO_SEG_VALID)) |
269 | blk_recount_segments(q, req->bio); |
270 | |
271 | return ll_new_hw_segment(q, req, bio); |
272 | } |
273 | |
274 | static int ll_merge_requests_fn(struct request_queue *q, struct request *req, |
275 | struct request *next) |
276 | { |
277 | int total_phys_segments; |
278 | unsigned int seg_size = |
279 | req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size; |
280 | |
281 | /* |
282 | * First check if the either of the requests are re-queued |
283 | * requests. Can't merge them if they are. |
284 | */ |
285 | if (req->special || next->special) |
286 | return 0; |
287 | |
288 | /* |
289 | * Will it become too large? |
290 | */ |
291 | if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q)) |
292 | return 0; |
293 | |
294 | total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; |
295 | if (blk_phys_contig_segment(q, req->biotail, next->bio)) { |
296 | if (req->nr_phys_segments == 1) |
297 | req->bio->bi_seg_front_size = seg_size; |
298 | if (next->nr_phys_segments == 1) |
299 | next->biotail->bi_seg_back_size = seg_size; |
300 | total_phys_segments--; |
301 | } |
302 | |
303 | if (total_phys_segments > queue_max_phys_segments(q)) |
304 | return 0; |
305 | |
306 | if (total_phys_segments > queue_max_hw_segments(q)) |
307 | return 0; |
308 | |
309 | /* Merge is OK... */ |
310 | req->nr_phys_segments = total_phys_segments; |
311 | return 1; |
312 | } |
313 | |
314 | static void blk_account_io_merge(struct request *req) |
315 | { |
316 | if (blk_do_io_stat(req)) { |
317 | struct hd_struct *part; |
318 | int cpu; |
319 | |
320 | cpu = part_stat_lock(); |
321 | part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); |
322 | |
323 | part_round_stats(cpu, part); |
324 | part_dec_in_flight(part); |
325 | |
326 | part_stat_unlock(); |
327 | } |
328 | } |
329 | |
330 | /* |
331 | * Has to be called with the request spinlock acquired |
332 | */ |
333 | static int attempt_merge(struct request_queue *q, struct request *req, |
334 | struct request *next) |
335 | { |
336 | if (!rq_mergeable(req) || !rq_mergeable(next)) |
337 | return 0; |
338 | |
339 | /* |
340 | * not contiguous |
341 | */ |
342 | if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) |
343 | return 0; |
344 | |
345 | if (rq_data_dir(req) != rq_data_dir(next) |
346 | || req->rq_disk != next->rq_disk |
347 | || next->special) |
348 | return 0; |
349 | |
350 | if (blk_integrity_rq(req) != blk_integrity_rq(next)) |
351 | return 0; |
352 | |
353 | /* don't merge requests of different failfast settings */ |
354 | if (blk_failfast_dev(req) != blk_failfast_dev(next) || |
355 | blk_failfast_transport(req) != blk_failfast_transport(next) || |
356 | blk_failfast_driver(req) != blk_failfast_driver(next)) |
357 | return 0; |
358 | |
359 | /* |
360 | * If we are allowed to merge, then append bio list |
361 | * from next to rq and release next. merge_requests_fn |
362 | * will have updated segment counts, update sector |
363 | * counts here. |
364 | */ |
365 | if (!ll_merge_requests_fn(q, req, next)) |
366 | return 0; |
367 | |
368 | /* |
369 | * At this point we have either done a back merge |
370 | * or front merge. We need the smaller start_time of |
371 | * the merged requests to be the current request |
372 | * for accounting purposes. |
373 | */ |
374 | if (time_after(req->start_time, next->start_time)) |
375 | req->start_time = next->start_time; |
376 | |
377 | req->biotail->bi_next = next->bio; |
378 | req->biotail = next->biotail; |
379 | |
380 | req->__data_len += blk_rq_bytes(next); |
381 | |
382 | elv_merge_requests(q, req, next); |
383 | |
384 | /* |
385 | * 'next' is going away, so update stats accordingly |
386 | */ |
387 | blk_account_io_merge(next); |
388 | |
389 | req->ioprio = ioprio_best(req->ioprio, next->ioprio); |
390 | if (blk_rq_cpu_valid(next)) |
391 | req->cpu = next->cpu; |
392 | |
393 | /* owner-ship of bio passed from next to req */ |
394 | next->bio = NULL; |
395 | __blk_put_request(q, next); |
396 | return 1; |
397 | } |
398 | |
399 | int attempt_back_merge(struct request_queue *q, struct request *rq) |
400 | { |
401 | struct request *next = elv_latter_request(q, rq); |
402 | |
403 | if (next) |
404 | return attempt_merge(q, rq, next); |
405 | |
406 | return 0; |
407 | } |
408 | |
409 | int attempt_front_merge(struct request_queue *q, struct request *rq) |
410 | { |
411 | struct request *prev = elv_former_request(q, rq); |
412 | |
413 | if (prev) |
414 | return attempt_merge(q, prev, rq); |
415 | |
416 | return 0; |
417 | } |
418 |
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