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

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