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    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            }
51new_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
72void blk_recalc_rq_segments(struct request *rq)
73{
74    rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
75}
76
77void 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}
86EXPORT_SYMBOL(blk_recount_segments);
87
88static 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 */
118int 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 {
148new_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}
201EXPORT_SYMBOL(blk_rq_map_sg);
202
203static 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_segments(q)) {
210        req->cmd_flags |= REQ_NOMERGE;
211        if (req == q->last_merge)
212            q->last_merge = NULL;
213        return 0;
214    }
215
216    /*
217     * This will form the start of a new hw segment. Bump both
218     * counters.
219     */
220    req->nr_phys_segments += nr_phys_segs;
221    return 1;
222}
223
224int ll_back_merge_fn(struct request_queue *q, struct request *req,
225             struct bio *bio)
226{
227    unsigned short max_sectors;
228
229    if (unlikely(blk_pc_request(req)))
230        max_sectors = queue_max_hw_sectors(q);
231    else
232        max_sectors = queue_max_sectors(q);
233
234    if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
235        req->cmd_flags |= REQ_NOMERGE;
236        if (req == q->last_merge)
237            q->last_merge = NULL;
238        return 0;
239    }
240    if (!bio_flagged(req->biotail, BIO_SEG_VALID))
241        blk_recount_segments(q, req->biotail);
242    if (!bio_flagged(bio, BIO_SEG_VALID))
243        blk_recount_segments(q, bio);
244
245    return ll_new_hw_segment(q, req, bio);
246}
247
248int ll_front_merge_fn(struct request_queue *q, struct request *req,
249              struct bio *bio)
250{
251    unsigned short max_sectors;
252
253    if (unlikely(blk_pc_request(req)))
254        max_sectors = queue_max_hw_sectors(q);
255    else
256        max_sectors = queue_max_sectors(q);
257
258
259    if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
260        req->cmd_flags |= REQ_NOMERGE;
261        if (req == q->last_merge)
262            q->last_merge = NULL;
263        return 0;
264    }
265    if (!bio_flagged(bio, BIO_SEG_VALID))
266        blk_recount_segments(q, bio);
267    if (!bio_flagged(req->bio, BIO_SEG_VALID))
268        blk_recount_segments(q, req->bio);
269
270    return ll_new_hw_segment(q, req, bio);
271}
272
273static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
274                struct request *next)
275{
276    int total_phys_segments;
277    unsigned int seg_size =
278        req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
279
280    /*
281     * First check if the either of the requests are re-queued
282     * requests. Can't merge them if they are.
283     */
284    if (req->special || next->special)
285        return 0;
286
287    /*
288     * Will it become too large?
289     */
290    if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q))
291        return 0;
292
293    total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
294    if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
295        if (req->nr_phys_segments == 1)
296            req->bio->bi_seg_front_size = seg_size;
297        if (next->nr_phys_segments == 1)
298            next->biotail->bi_seg_back_size = seg_size;
299        total_phys_segments--;
300    }
301
302    if (total_phys_segments > queue_max_segments(q))
303        return 0;
304
305    /* Merge is OK... */
306    req->nr_phys_segments = total_phys_segments;
307    return 1;
308}
309
310/**
311 * blk_rq_set_mixed_merge - mark a request as mixed merge
312 * @rq: request to mark as mixed merge
313 *
314 * Description:
315 * @rq is about to be mixed merged. Make sure the attributes
316 * which can be mixed are set in each bio and mark @rq as mixed
317 * merged.
318 */
319void blk_rq_set_mixed_merge(struct request *rq)
320{
321    unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
322    struct bio *bio;
323
324    if (rq->cmd_flags & REQ_MIXED_MERGE)
325        return;
326
327    /*
328     * @rq will no longer represent mixable attributes for all the
329     * contained bios. It will just track those of the first one.
330     * Distributes the attributs to each bio.
331     */
332    for (bio = rq->bio; bio; bio = bio->bi_next) {
333        WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
334                 (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
335        bio->bi_rw |= ff;
336    }
337    rq->cmd_flags |= REQ_MIXED_MERGE;
338}
339
340static void blk_account_io_merge(struct request *req)
341{
342    if (blk_do_io_stat(req)) {
343        struct hd_struct *part;
344        int cpu;
345
346        cpu = part_stat_lock();
347        part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req));
348
349        part_round_stats(cpu, part);
350        part_dec_in_flight(part, rq_data_dir(req));
351
352        part_stat_unlock();
353    }
354}
355
356/*
357 * Has to be called with the request spinlock acquired
358 */
359static int attempt_merge(struct request_queue *q, struct request *req,
360              struct request *next)
361{
362    if (!rq_mergeable(req) || !rq_mergeable(next))
363        return 0;
364
365    /*
366     * not contiguous
367     */
368    if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
369        return 0;
370
371    if (rq_data_dir(req) != rq_data_dir(next)
372        || req->rq_disk != next->rq_disk
373        || next->special)
374        return 0;
375
376    if (blk_integrity_rq(req) != blk_integrity_rq(next))
377        return 0;
378
379    /*
380     * If we are allowed to merge, then append bio list
381     * from next to rq and release next. merge_requests_fn
382     * will have updated segment counts, update sector
383     * counts here.
384     */
385    if (!ll_merge_requests_fn(q, req, next))
386        return 0;
387
388    /*
389     * If failfast settings disagree or any of the two is already
390     * a mixed merge, mark both as mixed before proceeding. This
391     * makes sure that all involved bios have mixable attributes
392     * set properly.
393     */
394    if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
395        (req->cmd_flags & REQ_FAILFAST_MASK) !=
396        (next->cmd_flags & REQ_FAILFAST_MASK)) {
397        blk_rq_set_mixed_merge(req);
398        blk_rq_set_mixed_merge(next);
399    }
400
401    /*
402     * At this point we have either done a back merge
403     * or front merge. We need the smaller start_time of
404     * the merged requests to be the current request
405     * for accounting purposes.
406     */
407    if (time_after(req->start_time, next->start_time))
408        req->start_time = next->start_time;
409
410    req->biotail->bi_next = next->bio;
411    req->biotail = next->biotail;
412
413    req->__data_len += blk_rq_bytes(next);
414
415    elv_merge_requests(q, req, next);
416
417    /*
418     * 'next' is going away, so update stats accordingly
419     */
420    blk_account_io_merge(next);
421
422    req->ioprio = ioprio_best(req->ioprio, next->ioprio);
423    if (blk_rq_cpu_valid(next))
424        req->cpu = next->cpu;
425
426    /* owner-ship of bio passed from next to req */
427    next->bio = NULL;
428    __blk_put_request(q, next);
429    return 1;
430}
431
432int attempt_back_merge(struct request_queue *q, struct request *rq)
433{
434    struct request *next = elv_latter_request(q, rq);
435
436    if (next)
437        return attempt_merge(q, rq, next);
438
439    return 0;
440}
441
442int attempt_front_merge(struct request_queue *q, struct request *rq)
443{
444    struct request *prev = elv_former_request(q, rq);
445
446    if (prev)
447        return attempt_merge(q, prev, rq);
448
449    return 0;
450}
451

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