Root/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
12static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
13                         struct bio *bio)
14{
15    struct bio_vec bv, bvprv = { NULL };
16    int cluster, high, highprv = 1, no_sg_merge;
17    unsigned int seg_size, nr_phys_segs;
18    struct bio *fbio, *bbio;
19    struct bvec_iter iter;
20
21    if (!bio)
22        return 0;
23
24    /*
25     * This should probably be returning 0, but blk_add_request_payload()
26     * (Christoph!!!!)
27     */
28    if (bio->bi_rw & REQ_DISCARD)
29        return 1;
30
31    if (bio->bi_rw & REQ_WRITE_SAME)
32        return 1;
33
34    fbio = bio;
35    cluster = blk_queue_cluster(q);
36    seg_size = 0;
37    nr_phys_segs = 0;
38    no_sg_merge = test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags);
39    high = 0;
40    for_each_bio(bio) {
41        bio_for_each_segment(bv, bio, iter) {
42            /*
43             * If SG merging is disabled, each bio vector is
44             * a segment
45             */
46            if (no_sg_merge)
47                goto new_segment;
48
49            /*
50             * the trick here is making sure that a high page is
51             * never considered part of another segment, since
52             * that might change with the bounce page.
53             */
54            high = page_to_pfn(bv.bv_page) > queue_bounce_pfn(q);
55            if (!high && !highprv && cluster) {
56                if (seg_size + bv.bv_len
57                    > queue_max_segment_size(q))
58                    goto new_segment;
59                if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
60                    goto new_segment;
61                if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
62                    goto new_segment;
63
64                seg_size += bv.bv_len;
65                bvprv = bv;
66                continue;
67            }
68new_segment:
69            if (nr_phys_segs == 1 && seg_size >
70                fbio->bi_seg_front_size)
71                fbio->bi_seg_front_size = seg_size;
72
73            nr_phys_segs++;
74            bvprv = bv;
75            seg_size = bv.bv_len;
76            highprv = high;
77        }
78        bbio = bio;
79    }
80
81    if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
82        fbio->bi_seg_front_size = seg_size;
83    if (seg_size > bbio->bi_seg_back_size)
84        bbio->bi_seg_back_size = seg_size;
85
86    return nr_phys_segs;
87}
88
89void blk_recalc_rq_segments(struct request *rq)
90{
91    rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
92}
93
94void blk_recount_segments(struct request_queue *q, struct bio *bio)
95{
96    if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags))
97        bio->bi_phys_segments = bio->bi_vcnt;
98    else {
99        struct bio *nxt = bio->bi_next;
100
101        bio->bi_next = NULL;
102        bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
103        bio->bi_next = nxt;
104    }
105
106    bio->bi_flags |= (1 << BIO_SEG_VALID);
107}
108EXPORT_SYMBOL(blk_recount_segments);
109
110static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
111                   struct bio *nxt)
112{
113    struct bio_vec end_bv = { NULL }, nxt_bv;
114    struct bvec_iter iter;
115
116    if (!blk_queue_cluster(q))
117        return 0;
118
119    if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
120        queue_max_segment_size(q))
121        return 0;
122
123    if (!bio_has_data(bio))
124        return 1;
125
126    bio_for_each_segment(end_bv, bio, iter)
127        if (end_bv.bv_len == iter.bi_size)
128            break;
129
130    nxt_bv = bio_iovec(nxt);
131
132    if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
133        return 0;
134
135    /*
136     * bio and nxt are contiguous in memory; check if the queue allows
137     * these two to be merged into one
138     */
139    if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
140        return 1;
141
142    return 0;
143}
144
145static inline void
146__blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
147             struct scatterlist *sglist, struct bio_vec *bvprv,
148             struct scatterlist **sg, int *nsegs, int *cluster)
149{
150
151    int nbytes = bvec->bv_len;
152
153    if (*sg && *cluster) {
154        if ((*sg)->length + nbytes > queue_max_segment_size(q))
155            goto new_segment;
156
157        if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
158            goto new_segment;
159        if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
160            goto new_segment;
161
162        (*sg)->length += nbytes;
163    } else {
164new_segment:
165        if (!*sg)
166            *sg = sglist;
167        else {
168            /*
169             * If the driver previously mapped a shorter
170             * list, we could see a termination bit
171             * prematurely unless it fully inits the sg
172             * table on each mapping. We KNOW that there
173             * must be more entries here or the driver
174             * would be buggy, so force clear the
175             * termination bit to avoid doing a full
176             * sg_init_table() in drivers for each command.
177             */
178            sg_unmark_end(*sg);
179            *sg = sg_next(*sg);
180        }
181
182        sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
183        (*nsegs)++;
184    }
185    *bvprv = *bvec;
186}
187
188static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
189                 struct scatterlist *sglist,
190                 struct scatterlist **sg)
191{
192    struct bio_vec bvec, bvprv = { NULL };
193    struct bvec_iter iter;
194    int nsegs, cluster;
195
196    nsegs = 0;
197    cluster = blk_queue_cluster(q);
198
199    if (bio->bi_rw & REQ_DISCARD) {
200        /*
201         * This is a hack - drivers should be neither modifying the
202         * biovec, nor relying on bi_vcnt - but because of
203         * blk_add_request_payload(), a discard bio may or may not have
204         * a payload we need to set up here (thank you Christoph) and
205         * bi_vcnt is really the only way of telling if we need to.
206         */
207
208        if (bio->bi_vcnt)
209            goto single_segment;
210
211        return 0;
212    }
213
214    if (bio->bi_rw & REQ_WRITE_SAME) {
215single_segment:
216        *sg = sglist;
217        bvec = bio_iovec(bio);
218        sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
219        return 1;
220    }
221
222    for_each_bio(bio)
223        bio_for_each_segment(bvec, bio, iter)
224            __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
225                         &nsegs, &cluster);
226
227    return nsegs;
228}
229
230/*
231 * map a request to scatterlist, return number of sg entries setup. Caller
232 * must make sure sg can hold rq->nr_phys_segments entries
233 */
234int blk_rq_map_sg(struct request_queue *q, struct request *rq,
235          struct scatterlist *sglist)
236{
237    struct scatterlist *sg = NULL;
238    int nsegs = 0;
239
240    if (rq->bio)
241        nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
242
243    if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
244        (blk_rq_bytes(rq) & q->dma_pad_mask)) {
245        unsigned int pad_len =
246            (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
247
248        sg->length += pad_len;
249        rq->extra_len += pad_len;
250    }
251
252    if (q->dma_drain_size && q->dma_drain_needed(rq)) {
253        if (rq->cmd_flags & REQ_WRITE)
254            memset(q->dma_drain_buffer, 0, q->dma_drain_size);
255
256        sg->page_link &= ~0x02;
257        sg = sg_next(sg);
258        sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
259                q->dma_drain_size,
260                ((unsigned long)q->dma_drain_buffer) &
261                (PAGE_SIZE - 1));
262        nsegs++;
263        rq->extra_len += q->dma_drain_size;
264    }
265
266    if (sg)
267        sg_mark_end(sg);
268
269    return nsegs;
270}
271EXPORT_SYMBOL(blk_rq_map_sg);
272
273/**
274 * blk_bio_map_sg - map a bio to a scatterlist
275 * @q: request_queue in question
276 * @bio: bio being mapped
277 * @sglist: scatterlist being mapped
278 *
279 * Note:
280 * Caller must make sure sg can hold bio->bi_phys_segments entries
281 *
282 * Will return the number of sg entries setup
283 */
284int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
285           struct scatterlist *sglist)
286{
287    struct scatterlist *sg = NULL;
288    int nsegs;
289    struct bio *next = bio->bi_next;
290    bio->bi_next = NULL;
291
292    nsegs = __blk_bios_map_sg(q, bio, sglist, &sg);
293    bio->bi_next = next;
294    if (sg)
295        sg_mark_end(sg);
296
297    BUG_ON(bio->bi_phys_segments && nsegs > bio->bi_phys_segments);
298    return nsegs;
299}
300EXPORT_SYMBOL(blk_bio_map_sg);
301
302static inline int ll_new_hw_segment(struct request_queue *q,
303                    struct request *req,
304                    struct bio *bio)
305{
306    int nr_phys_segs = bio_phys_segments(q, bio);
307
308    if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
309        goto no_merge;
310
311    if (bio_integrity(bio) && blk_integrity_merge_bio(q, req, bio))
312        goto no_merge;
313
314    /*
315     * This will form the start of a new hw segment. Bump both
316     * counters.
317     */
318    req->nr_phys_segments += nr_phys_segs;
319    return 1;
320
321no_merge:
322    req->cmd_flags |= REQ_NOMERGE;
323    if (req == q->last_merge)
324        q->last_merge = NULL;
325    return 0;
326}
327
328int ll_back_merge_fn(struct request_queue *q, struct request *req,
329             struct bio *bio)
330{
331    if (blk_rq_sectors(req) + bio_sectors(bio) >
332        blk_rq_get_max_sectors(req)) {
333        req->cmd_flags |= REQ_NOMERGE;
334        if (req == q->last_merge)
335            q->last_merge = NULL;
336        return 0;
337    }
338    if (!bio_flagged(req->biotail, BIO_SEG_VALID))
339        blk_recount_segments(q, req->biotail);
340    if (!bio_flagged(bio, BIO_SEG_VALID))
341        blk_recount_segments(q, bio);
342
343    return ll_new_hw_segment(q, req, bio);
344}
345
346int ll_front_merge_fn(struct request_queue *q, struct request *req,
347              struct bio *bio)
348{
349    if (blk_rq_sectors(req) + bio_sectors(bio) >
350        blk_rq_get_max_sectors(req)) {
351        req->cmd_flags |= REQ_NOMERGE;
352        if (req == q->last_merge)
353            q->last_merge = NULL;
354        return 0;
355    }
356    if (!bio_flagged(bio, BIO_SEG_VALID))
357        blk_recount_segments(q, bio);
358    if (!bio_flagged(req->bio, BIO_SEG_VALID))
359        blk_recount_segments(q, req->bio);
360
361    return ll_new_hw_segment(q, req, bio);
362}
363
364/*
365 * blk-mq uses req->special to carry normal driver per-request payload, it
366 * does not indicate a prepared command that we cannot merge with.
367 */
368static bool req_no_special_merge(struct request *req)
369{
370    struct request_queue *q = req->q;
371
372    return !q->mq_ops && req->special;
373}
374
375static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
376                struct request *next)
377{
378    int total_phys_segments;
379    unsigned int seg_size =
380        req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
381
382    /*
383     * First check if the either of the requests are re-queued
384     * requests. Can't merge them if they are.
385     */
386    if (req_no_special_merge(req) || req_no_special_merge(next))
387        return 0;
388
389    /*
390     * Will it become too large?
391     */
392    if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
393        blk_rq_get_max_sectors(req))
394        return 0;
395
396    total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
397    if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
398        if (req->nr_phys_segments == 1)
399            req->bio->bi_seg_front_size = seg_size;
400        if (next->nr_phys_segments == 1)
401            next->biotail->bi_seg_back_size = seg_size;
402        total_phys_segments--;
403    }
404
405    if (total_phys_segments > queue_max_segments(q))
406        return 0;
407
408    if (blk_integrity_rq(req) && blk_integrity_merge_rq(q, req, next))
409        return 0;
410
411    /* Merge is OK... */
412    req->nr_phys_segments = total_phys_segments;
413    return 1;
414}
415
416/**
417 * blk_rq_set_mixed_merge - mark a request as mixed merge
418 * @rq: request to mark as mixed merge
419 *
420 * Description:
421 * @rq is about to be mixed merged. Make sure the attributes
422 * which can be mixed are set in each bio and mark @rq as mixed
423 * merged.
424 */
425void blk_rq_set_mixed_merge(struct request *rq)
426{
427    unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
428    struct bio *bio;
429
430    if (rq->cmd_flags & REQ_MIXED_MERGE)
431        return;
432
433    /*
434     * @rq will no longer represent mixable attributes for all the
435     * contained bios. It will just track those of the first one.
436     * Distributes the attributs to each bio.
437     */
438    for (bio = rq->bio; bio; bio = bio->bi_next) {
439        WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
440                 (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
441        bio->bi_rw |= ff;
442    }
443    rq->cmd_flags |= REQ_MIXED_MERGE;
444}
445
446static void blk_account_io_merge(struct request *req)
447{
448    if (blk_do_io_stat(req)) {
449        struct hd_struct *part;
450        int cpu;
451
452        cpu = part_stat_lock();
453        part = req->part;
454
455        part_round_stats(cpu, part);
456        part_dec_in_flight(part, rq_data_dir(req));
457
458        hd_struct_put(part);
459        part_stat_unlock();
460    }
461}
462
463/*
464 * Has to be called with the request spinlock acquired
465 */
466static int attempt_merge(struct request_queue *q, struct request *req,
467              struct request *next)
468{
469    if (!rq_mergeable(req) || !rq_mergeable(next))
470        return 0;
471
472    if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
473        return 0;
474
475    /*
476     * not contiguous
477     */
478    if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
479        return 0;
480
481    if (rq_data_dir(req) != rq_data_dir(next)
482        || req->rq_disk != next->rq_disk
483        || req_no_special_merge(next))
484        return 0;
485
486    if (req->cmd_flags & REQ_WRITE_SAME &&
487        !blk_write_same_mergeable(req->bio, next->bio))
488        return 0;
489
490    /*
491     * If we are allowed to merge, then append bio list
492     * from next to rq and release next. merge_requests_fn
493     * will have updated segment counts, update sector
494     * counts here.
495     */
496    if (!ll_merge_requests_fn(q, req, next))
497        return 0;
498
499    /*
500     * If failfast settings disagree or any of the two is already
501     * a mixed merge, mark both as mixed before proceeding. This
502     * makes sure that all involved bios have mixable attributes
503     * set properly.
504     */
505    if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
506        (req->cmd_flags & REQ_FAILFAST_MASK) !=
507        (next->cmd_flags & REQ_FAILFAST_MASK)) {
508        blk_rq_set_mixed_merge(req);
509        blk_rq_set_mixed_merge(next);
510    }
511
512    /*
513     * At this point we have either done a back merge
514     * or front merge. We need the smaller start_time of
515     * the merged requests to be the current request
516     * for accounting purposes.
517     */
518    if (time_after(req->start_time, next->start_time))
519        req->start_time = next->start_time;
520
521    req->biotail->bi_next = next->bio;
522    req->biotail = next->biotail;
523
524    req->__data_len += blk_rq_bytes(next);
525
526    elv_merge_requests(q, req, next);
527
528    /*
529     * 'next' is going away, so update stats accordingly
530     */
531    blk_account_io_merge(next);
532
533    req->ioprio = ioprio_best(req->ioprio, next->ioprio);
534    if (blk_rq_cpu_valid(next))
535        req->cpu = next->cpu;
536
537    /* owner-ship of bio passed from next to req */
538    next->bio = NULL;
539    __blk_put_request(q, next);
540    return 1;
541}
542
543int attempt_back_merge(struct request_queue *q, struct request *rq)
544{
545    struct request *next = elv_latter_request(q, rq);
546
547    if (next)
548        return attempt_merge(q, rq, next);
549
550    return 0;
551}
552
553int attempt_front_merge(struct request_queue *q, struct request *rq)
554{
555    struct request *prev = elv_former_request(q, rq);
556
557    if (prev)
558        return attempt_merge(q, prev, rq);
559
560    return 0;
561}
562
563int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
564              struct request *next)
565{
566    return attempt_merge(q, rq, next);
567}
568
569bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
570{
571    struct request_queue *q = rq->q;
572
573    if (!rq_mergeable(rq) || !bio_mergeable(bio))
574        return false;
575
576    if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
577        return false;
578
579    /* different data direction or already started, don't merge */
580    if (bio_data_dir(bio) != rq_data_dir(rq))
581        return false;
582
583    /* must be same device and not a special request */
584    if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
585        return false;
586
587    /* only merge integrity protected bio into ditto rq */
588    if (bio_integrity(bio) != blk_integrity_rq(rq))
589        return false;
590
591    /* must be using the same buffer */
592    if (rq->cmd_flags & REQ_WRITE_SAME &&
593        !blk_write_same_mergeable(rq->bio, bio))
594        return false;
595
596    if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS)) {
597        struct bio_vec *bprev;
598
599        bprev = &rq->biotail->bi_io_vec[bio->bi_vcnt - 1];
600        if (bvec_gap_to_prev(bprev, bio->bi_io_vec[0].bv_offset))
601            return false;
602    }
603
604    return true;
605}
606
607int blk_try_merge(struct request *rq, struct bio *bio)
608{
609    if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
610        return ELEVATOR_BACK_MERGE;
611    else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
612        return ELEVATOR_FRONT_MERGE;
613    return ELEVATOR_NO_MERGE;
614}
615

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