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TOMOYO Linux Cross Reference
Linux/fs/btrfs/reada.c

Version: ~ [ linux-5.19-rc3 ] ~ [ linux-5.18.5 ] ~ [ linux-5.17.15 ] ~ [ linux-5.16.20 ] ~ [ linux-5.15.48 ] ~ [ linux-5.14.21 ] ~ [ linux-5.13.19 ] ~ [ linux-5.12.19 ] ~ [ linux-5.11.22 ] ~ [ linux-5.10.123 ] ~ [ linux-5.9.16 ] ~ [ linux-5.8.18 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.199 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.248 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.284 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.319 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.302 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.9 ] ~ [ policy-sample ] ~
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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * Copyright (C) 2011 STRATO.  All rights reserved.
  4  */
  5 
  6 #include <linux/sched.h>
  7 #include <linux/pagemap.h>
  8 #include <linux/writeback.h>
  9 #include <linux/blkdev.h>
 10 #include <linux/slab.h>
 11 #include <linux/workqueue.h>
 12 #include "ctree.h"
 13 #include "volumes.h"
 14 #include "disk-io.h"
 15 #include "transaction.h"
 16 #include "dev-replace.h"
 17 
 18 #undef DEBUG
 19 
 20 /*
 21  * This is the implementation for the generic read ahead framework.
 22  *
 23  * To trigger a readahead, btrfs_reada_add must be called. It will start
 24  * a read ahead for the given range [start, end) on tree root. The returned
 25  * handle can either be used to wait on the readahead to finish
 26  * (btrfs_reada_wait), or to send it to the background (btrfs_reada_detach).
 27  *
 28  * The read ahead works as follows:
 29  * On btrfs_reada_add, the root of the tree is inserted into a radix_tree.
 30  * reada_start_machine will then search for extents to prefetch and trigger
 31  * some reads. When a read finishes for a node, all contained node/leaf
 32  * pointers that lie in the given range will also be enqueued. The reads will
 33  * be triggered in sequential order, thus giving a big win over a naive
 34  * enumeration. It will also make use of multi-device layouts. Each disk
 35  * will have its on read pointer and all disks will by utilized in parallel.
 36  * Also will no two disks read both sides of a mirror simultaneously, as this
 37  * would waste seeking capacity. Instead both disks will read different parts
 38  * of the filesystem.
 39  * Any number of readaheads can be started in parallel. The read order will be
 40  * determined globally, i.e. 2 parallel readaheads will normally finish faster
 41  * than the 2 started one after another.
 42  */
 43 
 44 #define MAX_IN_FLIGHT 6
 45 
 46 struct reada_extctl {
 47         struct list_head        list;
 48         struct reada_control    *rc;
 49         u64                     generation;
 50 };
 51 
 52 struct reada_extent {
 53         u64                     logical;
 54         struct btrfs_key        top;
 55         struct list_head        extctl;
 56         int                     refcnt;
 57         spinlock_t              lock;
 58         struct reada_zone       *zones[BTRFS_MAX_MIRRORS];
 59         int                     nzones;
 60         int                     scheduled;
 61 };
 62 
 63 struct reada_zone {
 64         u64                     start;
 65         u64                     end;
 66         u64                     elems;
 67         struct list_head        list;
 68         spinlock_t              lock;
 69         int                     locked;
 70         struct btrfs_device     *device;
 71         struct btrfs_device     *devs[BTRFS_MAX_MIRRORS]; /* full list, incl
 72                                                            * self */
 73         int                     ndevs;
 74         struct kref             refcnt;
 75 };
 76 
 77 struct reada_machine_work {
 78         struct btrfs_work       work;
 79         struct btrfs_fs_info    *fs_info;
 80 };
 81 
 82 static void reada_extent_put(struct btrfs_fs_info *, struct reada_extent *);
 83 static void reada_control_release(struct kref *kref);
 84 static void reada_zone_release(struct kref *kref);
 85 static void reada_start_machine(struct btrfs_fs_info *fs_info);
 86 static void __reada_start_machine(struct btrfs_fs_info *fs_info);
 87 
 88 static int reada_add_block(struct reada_control *rc, u64 logical,
 89                            struct btrfs_key *top, u64 generation);
 90 
 91 /* recurses */
 92 /* in case of err, eb might be NULL */
 93 static void __readahead_hook(struct btrfs_fs_info *fs_info,
 94                              struct reada_extent *re, struct extent_buffer *eb,
 95                              int err)
 96 {
 97         int nritems;
 98         int i;
 99         u64 bytenr;
100         u64 generation;
101         struct list_head list;
102 
103         spin_lock(&re->lock);
104         /*
105          * just take the full list from the extent. afterwards we
106          * don't need the lock anymore
107          */
108         list_replace_init(&re->extctl, &list);
109         re->scheduled = 0;
110         spin_unlock(&re->lock);
111 
112         /*
113          * this is the error case, the extent buffer has not been
114          * read correctly. We won't access anything from it and
115          * just cleanup our data structures. Effectively this will
116          * cut the branch below this node from read ahead.
117          */
118         if (err)
119                 goto cleanup;
120 
121         /*
122          * FIXME: currently we just set nritems to 0 if this is a leaf,
123          * effectively ignoring the content. In a next step we could
124          * trigger more readahead depending from the content, e.g.
125          * fetch the checksums for the extents in the leaf.
126          */
127         if (!btrfs_header_level(eb))
128                 goto cleanup;
129 
130         nritems = btrfs_header_nritems(eb);
131         generation = btrfs_header_generation(eb);
132         for (i = 0; i < nritems; i++) {
133                 struct reada_extctl *rec;
134                 u64 n_gen;
135                 struct btrfs_key key;
136                 struct btrfs_key next_key;
137 
138                 btrfs_node_key_to_cpu(eb, &key, i);
139                 if (i + 1 < nritems)
140                         btrfs_node_key_to_cpu(eb, &next_key, i + 1);
141                 else
142                         next_key = re->top;
143                 bytenr = btrfs_node_blockptr(eb, i);
144                 n_gen = btrfs_node_ptr_generation(eb, i);
145 
146                 list_for_each_entry(rec, &list, list) {
147                         struct reada_control *rc = rec->rc;
148 
149                         /*
150                          * if the generation doesn't match, just ignore this
151                          * extctl. This will probably cut off a branch from
152                          * prefetch. Alternatively one could start a new (sub-)
153                          * prefetch for this branch, starting again from root.
154                          * FIXME: move the generation check out of this loop
155                          */
156 #ifdef DEBUG
157                         if (rec->generation != generation) {
158                                 btrfs_debug(fs_info,
159                                             "generation mismatch for (%llu,%d,%llu) %llu != %llu",
160                                             key.objectid, key.type, key.offset,
161                                             rec->generation, generation);
162                         }
163 #endif
164                         if (rec->generation == generation &&
165                             btrfs_comp_cpu_keys(&key, &rc->key_end) < 0 &&
166                             btrfs_comp_cpu_keys(&next_key, &rc->key_start) > 0)
167                                 reada_add_block(rc, bytenr, &next_key, n_gen);
168                 }
169         }
170 
171 cleanup:
172         /*
173          * free extctl records
174          */
175         while (!list_empty(&list)) {
176                 struct reada_control *rc;
177                 struct reada_extctl *rec;
178 
179                 rec = list_first_entry(&list, struct reada_extctl, list);
180                 list_del(&rec->list);
181                 rc = rec->rc;
182                 kfree(rec);
183 
184                 kref_get(&rc->refcnt);
185                 if (atomic_dec_and_test(&rc->elems)) {
186                         kref_put(&rc->refcnt, reada_control_release);
187                         wake_up(&rc->wait);
188                 }
189                 kref_put(&rc->refcnt, reada_control_release);
190 
191                 reada_extent_put(fs_info, re);  /* one ref for each entry */
192         }
193 
194         return;
195 }
196 
197 int btree_readahead_hook(struct extent_buffer *eb, int err)
198 {
199         struct btrfs_fs_info *fs_info = eb->fs_info;
200         int ret = 0;
201         struct reada_extent *re;
202 
203         /* find extent */
204         spin_lock(&fs_info->reada_lock);
205         re = radix_tree_lookup(&fs_info->reada_tree,
206                                eb->start >> PAGE_SHIFT);
207         if (re)
208                 re->refcnt++;
209         spin_unlock(&fs_info->reada_lock);
210         if (!re) {
211                 ret = -1;
212                 goto start_machine;
213         }
214 
215         __readahead_hook(fs_info, re, eb, err);
216         reada_extent_put(fs_info, re);  /* our ref */
217 
218 start_machine:
219         reada_start_machine(fs_info);
220         return ret;
221 }
222 
223 static struct reada_zone *reada_find_zone(struct btrfs_device *dev, u64 logical,
224                                           struct btrfs_bio *bbio)
225 {
226         struct btrfs_fs_info *fs_info = dev->fs_info;
227         int ret;
228         struct reada_zone *zone;
229         struct btrfs_block_group_cache *cache = NULL;
230         u64 start;
231         u64 end;
232         int i;
233 
234         zone = NULL;
235         spin_lock(&fs_info->reada_lock);
236         ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
237                                      logical >> PAGE_SHIFT, 1);
238         if (ret == 1 && logical >= zone->start && logical <= zone->end) {
239                 kref_get(&zone->refcnt);
240                 spin_unlock(&fs_info->reada_lock);
241                 return zone;
242         }
243 
244         spin_unlock(&fs_info->reada_lock);
245 
246         cache = btrfs_lookup_block_group(fs_info, logical);
247         if (!cache)
248                 return NULL;
249 
250         start = cache->key.objectid;
251         end = start + cache->key.offset - 1;
252         btrfs_put_block_group(cache);
253 
254         zone = kzalloc(sizeof(*zone), GFP_KERNEL);
255         if (!zone)
256                 return NULL;
257 
258         ret = radix_tree_preload(GFP_KERNEL);
259         if (ret) {
260                 kfree(zone);
261                 return NULL;
262         }
263 
264         zone->start = start;
265         zone->end = end;
266         INIT_LIST_HEAD(&zone->list);
267         spin_lock_init(&zone->lock);
268         zone->locked = 0;
269         kref_init(&zone->refcnt);
270         zone->elems = 0;
271         zone->device = dev; /* our device always sits at index 0 */
272         for (i = 0; i < bbio->num_stripes; ++i) {
273                 /* bounds have already been checked */
274                 zone->devs[i] = bbio->stripes[i].dev;
275         }
276         zone->ndevs = bbio->num_stripes;
277 
278         spin_lock(&fs_info->reada_lock);
279         ret = radix_tree_insert(&dev->reada_zones,
280                                 (unsigned long)(zone->end >> PAGE_SHIFT),
281                                 zone);
282 
283         if (ret == -EEXIST) {
284                 kfree(zone);
285                 ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
286                                              logical >> PAGE_SHIFT, 1);
287                 if (ret == 1 && logical >= zone->start && logical <= zone->end)
288                         kref_get(&zone->refcnt);
289                 else
290                         zone = NULL;
291         }
292         spin_unlock(&fs_info->reada_lock);
293         radix_tree_preload_end();
294 
295         return zone;
296 }
297 
298 static struct reada_extent *reada_find_extent(struct btrfs_fs_info *fs_info,
299                                               u64 logical,
300                                               struct btrfs_key *top)
301 {
302         int ret;
303         struct reada_extent *re = NULL;
304         struct reada_extent *re_exist = NULL;
305         struct btrfs_bio *bbio = NULL;
306         struct btrfs_device *dev;
307         struct btrfs_device *prev_dev;
308         u64 length;
309         int real_stripes;
310         int nzones = 0;
311         unsigned long index = logical >> PAGE_SHIFT;
312         int dev_replace_is_ongoing;
313         int have_zone = 0;
314 
315         spin_lock(&fs_info->reada_lock);
316         re = radix_tree_lookup(&fs_info->reada_tree, index);
317         if (re)
318                 re->refcnt++;
319         spin_unlock(&fs_info->reada_lock);
320 
321         if (re)
322                 return re;
323 
324         re = kzalloc(sizeof(*re), GFP_KERNEL);
325         if (!re)
326                 return NULL;
327 
328         re->logical = logical;
329         re->top = *top;
330         INIT_LIST_HEAD(&re->extctl);
331         spin_lock_init(&re->lock);
332         re->refcnt = 1;
333 
334         /*
335          * map block
336          */
337         length = fs_info->nodesize;
338         ret = btrfs_map_block(fs_info, BTRFS_MAP_GET_READ_MIRRORS, logical,
339                         &length, &bbio, 0);
340         if (ret || !bbio || length < fs_info->nodesize)
341                 goto error;
342 
343         if (bbio->num_stripes > BTRFS_MAX_MIRRORS) {
344                 btrfs_err(fs_info,
345                            "readahead: more than %d copies not supported",
346                            BTRFS_MAX_MIRRORS);
347                 goto error;
348         }
349 
350         real_stripes = bbio->num_stripes - bbio->num_tgtdevs;
351         for (nzones = 0; nzones < real_stripes; ++nzones) {
352                 struct reada_zone *zone;
353 
354                 dev = bbio->stripes[nzones].dev;
355 
356                 /* cannot read ahead on missing device. */
357                 if (!dev->bdev)
358                         continue;
359 
360                 zone = reada_find_zone(dev, logical, bbio);
361                 if (!zone)
362                         continue;
363 
364                 re->zones[re->nzones++] = zone;
365                 spin_lock(&zone->lock);
366                 if (!zone->elems)
367                         kref_get(&zone->refcnt);
368                 ++zone->elems;
369                 spin_unlock(&zone->lock);
370                 spin_lock(&fs_info->reada_lock);
371                 kref_put(&zone->refcnt, reada_zone_release);
372                 spin_unlock(&fs_info->reada_lock);
373         }
374         if (re->nzones == 0) {
375                 /* not a single zone found, error and out */
376                 goto error;
377         }
378 
379         /* Insert extent in reada tree + all per-device trees, all or nothing */
380         down_read(&fs_info->dev_replace.rwsem);
381         ret = radix_tree_preload(GFP_KERNEL);
382         if (ret) {
383                 up_read(&fs_info->dev_replace.rwsem);
384                 goto error;
385         }
386 
387         spin_lock(&fs_info->reada_lock);
388         ret = radix_tree_insert(&fs_info->reada_tree, index, re);
389         if (ret == -EEXIST) {
390                 re_exist = radix_tree_lookup(&fs_info->reada_tree, index);
391                 re_exist->refcnt++;
392                 spin_unlock(&fs_info->reada_lock);
393                 radix_tree_preload_end();
394                 up_read(&fs_info->dev_replace.rwsem);
395                 goto error;
396         }
397         if (ret) {
398                 spin_unlock(&fs_info->reada_lock);
399                 radix_tree_preload_end();
400                 up_read(&fs_info->dev_replace.rwsem);
401                 goto error;
402         }
403         radix_tree_preload_end();
404         prev_dev = NULL;
405         dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(
406                         &fs_info->dev_replace);
407         for (nzones = 0; nzones < re->nzones; ++nzones) {
408                 dev = re->zones[nzones]->device;
409 
410                 if (dev == prev_dev) {
411                         /*
412                          * in case of DUP, just add the first zone. As both
413                          * are on the same device, there's nothing to gain
414                          * from adding both.
415                          * Also, it wouldn't work, as the tree is per device
416                          * and adding would fail with EEXIST
417                          */
418                         continue;
419                 }
420                 if (!dev->bdev)
421                         continue;
422 
423                 if (dev_replace_is_ongoing &&
424                     dev == fs_info->dev_replace.tgtdev) {
425                         /*
426                          * as this device is selected for reading only as
427                          * a last resort, skip it for read ahead.
428                          */
429                         continue;
430                 }
431                 prev_dev = dev;
432                 ret = radix_tree_insert(&dev->reada_extents, index, re);
433                 if (ret) {
434                         while (--nzones >= 0) {
435                                 dev = re->zones[nzones]->device;
436                                 BUG_ON(dev == NULL);
437                                 /* ignore whether the entry was inserted */
438                                 radix_tree_delete(&dev->reada_extents, index);
439                         }
440                         radix_tree_delete(&fs_info->reada_tree, index);
441                         spin_unlock(&fs_info->reada_lock);
442                         up_read(&fs_info->dev_replace.rwsem);
443                         goto error;
444                 }
445                 have_zone = 1;
446         }
447         spin_unlock(&fs_info->reada_lock);
448         up_read(&fs_info->dev_replace.rwsem);
449 
450         if (!have_zone)
451                 goto error;
452 
453         btrfs_put_bbio(bbio);
454         return re;
455 
456 error:
457         for (nzones = 0; nzones < re->nzones; ++nzones) {
458                 struct reada_zone *zone;
459 
460                 zone = re->zones[nzones];
461                 kref_get(&zone->refcnt);
462                 spin_lock(&zone->lock);
463                 --zone->elems;
464                 if (zone->elems == 0) {
465                         /*
466                          * no fs_info->reada_lock needed, as this can't be
467                          * the last ref
468                          */
469                         kref_put(&zone->refcnt, reada_zone_release);
470                 }
471                 spin_unlock(&zone->lock);
472 
473                 spin_lock(&fs_info->reada_lock);
474                 kref_put(&zone->refcnt, reada_zone_release);
475                 spin_unlock(&fs_info->reada_lock);
476         }
477         btrfs_put_bbio(bbio);
478         kfree(re);
479         return re_exist;
480 }
481 
482 static void reada_extent_put(struct btrfs_fs_info *fs_info,
483                              struct reada_extent *re)
484 {
485         int i;
486         unsigned long index = re->logical >> PAGE_SHIFT;
487 
488         spin_lock(&fs_info->reada_lock);
489         if (--re->refcnt) {
490                 spin_unlock(&fs_info->reada_lock);
491                 return;
492         }
493 
494         radix_tree_delete(&fs_info->reada_tree, index);
495         for (i = 0; i < re->nzones; ++i) {
496                 struct reada_zone *zone = re->zones[i];
497 
498                 radix_tree_delete(&zone->device->reada_extents, index);
499         }
500 
501         spin_unlock(&fs_info->reada_lock);
502 
503         for (i = 0; i < re->nzones; ++i) {
504                 struct reada_zone *zone = re->zones[i];
505 
506                 kref_get(&zone->refcnt);
507                 spin_lock(&zone->lock);
508                 --zone->elems;
509                 if (zone->elems == 0) {
510                         /* no fs_info->reada_lock needed, as this can't be
511                          * the last ref */
512                         kref_put(&zone->refcnt, reada_zone_release);
513                 }
514                 spin_unlock(&zone->lock);
515 
516                 spin_lock(&fs_info->reada_lock);
517                 kref_put(&zone->refcnt, reada_zone_release);
518                 spin_unlock(&fs_info->reada_lock);
519         }
520 
521         kfree(re);
522 }
523 
524 static void reada_zone_release(struct kref *kref)
525 {
526         struct reada_zone *zone = container_of(kref, struct reada_zone, refcnt);
527 
528         radix_tree_delete(&zone->device->reada_zones,
529                           zone->end >> PAGE_SHIFT);
530 
531         kfree(zone);
532 }
533 
534 static void reada_control_release(struct kref *kref)
535 {
536         struct reada_control *rc = container_of(kref, struct reada_control,
537                                                 refcnt);
538 
539         kfree(rc);
540 }
541 
542 static int reada_add_block(struct reada_control *rc, u64 logical,
543                            struct btrfs_key *top, u64 generation)
544 {
545         struct btrfs_fs_info *fs_info = rc->fs_info;
546         struct reada_extent *re;
547         struct reada_extctl *rec;
548 
549         /* takes one ref */
550         re = reada_find_extent(fs_info, logical, top);
551         if (!re)
552                 return -1;
553 
554         rec = kzalloc(sizeof(*rec), GFP_KERNEL);
555         if (!rec) {
556                 reada_extent_put(fs_info, re);
557                 return -ENOMEM;
558         }
559 
560         rec->rc = rc;
561         rec->generation = generation;
562         atomic_inc(&rc->elems);
563 
564         spin_lock(&re->lock);
565         list_add_tail(&rec->list, &re->extctl);
566         spin_unlock(&re->lock);
567 
568         /* leave the ref on the extent */
569 
570         return 0;
571 }
572 
573 /*
574  * called with fs_info->reada_lock held
575  */
576 static void reada_peer_zones_set_lock(struct reada_zone *zone, int lock)
577 {
578         int i;
579         unsigned long index = zone->end >> PAGE_SHIFT;
580 
581         for (i = 0; i < zone->ndevs; ++i) {
582                 struct reada_zone *peer;
583                 peer = radix_tree_lookup(&zone->devs[i]->reada_zones, index);
584                 if (peer && peer->device != zone->device)
585                         peer->locked = lock;
586         }
587 }
588 
589 /*
590  * called with fs_info->reada_lock held
591  */
592 static int reada_pick_zone(struct btrfs_device *dev)
593 {
594         struct reada_zone *top_zone = NULL;
595         struct reada_zone *top_locked_zone = NULL;
596         u64 top_elems = 0;
597         u64 top_locked_elems = 0;
598         unsigned long index = 0;
599         int ret;
600 
601         if (dev->reada_curr_zone) {
602                 reada_peer_zones_set_lock(dev->reada_curr_zone, 0);
603                 kref_put(&dev->reada_curr_zone->refcnt, reada_zone_release);
604                 dev->reada_curr_zone = NULL;
605         }
606         /* pick the zone with the most elements */
607         while (1) {
608                 struct reada_zone *zone;
609 
610                 ret = radix_tree_gang_lookup(&dev->reada_zones,
611                                              (void **)&zone, index, 1);
612                 if (ret == 0)
613                         break;
614                 index = (zone->end >> PAGE_SHIFT) + 1;
615                 if (zone->locked) {
616                         if (zone->elems > top_locked_elems) {
617                                 top_locked_elems = zone->elems;
618                                 top_locked_zone = zone;
619                         }
620                 } else {
621                         if (zone->elems > top_elems) {
622                                 top_elems = zone->elems;
623                                 top_zone = zone;
624                         }
625                 }
626         }
627         if (top_zone)
628                 dev->reada_curr_zone = top_zone;
629         else if (top_locked_zone)
630                 dev->reada_curr_zone = top_locked_zone;
631         else
632                 return 0;
633 
634         dev->reada_next = dev->reada_curr_zone->start;
635         kref_get(&dev->reada_curr_zone->refcnt);
636         reada_peer_zones_set_lock(dev->reada_curr_zone, 1);
637 
638         return 1;
639 }
640 
641 static int reada_start_machine_dev(struct btrfs_device *dev)
642 {
643         struct btrfs_fs_info *fs_info = dev->fs_info;
644         struct reada_extent *re = NULL;
645         int mirror_num = 0;
646         struct extent_buffer *eb = NULL;
647         u64 logical;
648         int ret;
649         int i;
650 
651         spin_lock(&fs_info->reada_lock);
652         if (dev->reada_curr_zone == NULL) {
653                 ret = reada_pick_zone(dev);
654                 if (!ret) {
655                         spin_unlock(&fs_info->reada_lock);
656                         return 0;
657                 }
658         }
659         /*
660          * FIXME currently we issue the reads one extent at a time. If we have
661          * a contiguous block of extents, we could also coagulate them or use
662          * plugging to speed things up
663          */
664         ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
665                                      dev->reada_next >> PAGE_SHIFT, 1);
666         if (ret == 0 || re->logical > dev->reada_curr_zone->end) {
667                 ret = reada_pick_zone(dev);
668                 if (!ret) {
669                         spin_unlock(&fs_info->reada_lock);
670                         return 0;
671                 }
672                 re = NULL;
673                 ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
674                                         dev->reada_next >> PAGE_SHIFT, 1);
675         }
676         if (ret == 0) {
677                 spin_unlock(&fs_info->reada_lock);
678                 return 0;
679         }
680         dev->reada_next = re->logical + fs_info->nodesize;
681         re->refcnt++;
682 
683         spin_unlock(&fs_info->reada_lock);
684 
685         spin_lock(&re->lock);
686         if (re->scheduled || list_empty(&re->extctl)) {
687                 spin_unlock(&re->lock);
688                 reada_extent_put(fs_info, re);
689                 return 0;
690         }
691         re->scheduled = 1;
692         spin_unlock(&re->lock);
693 
694         /*
695          * find mirror num
696          */
697         for (i = 0; i < re->nzones; ++i) {
698                 if (re->zones[i]->device == dev) {
699                         mirror_num = i + 1;
700                         break;
701                 }
702         }
703         logical = re->logical;
704 
705         atomic_inc(&dev->reada_in_flight);
706         ret = reada_tree_block_flagged(fs_info, logical, mirror_num, &eb);
707         if (ret)
708                 __readahead_hook(fs_info, re, NULL, ret);
709         else if (eb)
710                 __readahead_hook(fs_info, re, eb, ret);
711 
712         if (eb)
713                 free_extent_buffer(eb);
714 
715         atomic_dec(&dev->reada_in_flight);
716         reada_extent_put(fs_info, re);
717 
718         return 1;
719 
720 }
721 
722 static void reada_start_machine_worker(struct btrfs_work *work)
723 {
724         struct reada_machine_work *rmw;
725         struct btrfs_fs_info *fs_info;
726         int old_ioprio;
727 
728         rmw = container_of(work, struct reada_machine_work, work);
729         fs_info = rmw->fs_info;
730 
731         kfree(rmw);
732 
733         old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
734                                        task_nice_ioprio(current));
735         set_task_ioprio(current, BTRFS_IOPRIO_READA);
736         __reada_start_machine(fs_info);
737         set_task_ioprio(current, old_ioprio);
738 
739         atomic_dec(&fs_info->reada_works_cnt);
740 }
741 
742 static void __reada_start_machine(struct btrfs_fs_info *fs_info)
743 {
744         struct btrfs_device *device;
745         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
746         u64 enqueued;
747         u64 total = 0;
748         int i;
749 
750 again:
751         do {
752                 enqueued = 0;
753                 mutex_lock(&fs_devices->device_list_mutex);
754                 list_for_each_entry(device, &fs_devices->devices, dev_list) {
755                         if (atomic_read(&device->reada_in_flight) <
756                             MAX_IN_FLIGHT)
757                                 enqueued += reada_start_machine_dev(device);
758                 }
759                 mutex_unlock(&fs_devices->device_list_mutex);
760                 total += enqueued;
761         } while (enqueued && total < 10000);
762         if (fs_devices->seed) {
763                 fs_devices = fs_devices->seed;
764                 goto again;
765         }
766 
767         if (enqueued == 0)
768                 return;
769 
770         /*
771          * If everything is already in the cache, this is effectively single
772          * threaded. To a) not hold the caller for too long and b) to utilize
773          * more cores, we broke the loop above after 10000 iterations and now
774          * enqueue to workers to finish it. This will distribute the load to
775          * the cores.
776          */
777         for (i = 0; i < 2; ++i) {
778                 reada_start_machine(fs_info);
779                 if (atomic_read(&fs_info->reada_works_cnt) >
780                     BTRFS_MAX_MIRRORS * 2)
781                         break;
782         }
783 }
784 
785 static void reada_start_machine(struct btrfs_fs_info *fs_info)
786 {
787         struct reada_machine_work *rmw;
788 
789         rmw = kzalloc(sizeof(*rmw), GFP_KERNEL);
790         if (!rmw) {
791                 /* FIXME we cannot handle this properly right now */
792                 BUG();
793         }
794         btrfs_init_work(&rmw->work, btrfs_readahead_helper,
795                         reada_start_machine_worker, NULL, NULL);
796         rmw->fs_info = fs_info;
797 
798         btrfs_queue_work(fs_info->readahead_workers, &rmw->work);
799         atomic_inc(&fs_info->reada_works_cnt);
800 }
801 
802 #ifdef DEBUG
803 static void dump_devs(struct btrfs_fs_info *fs_info, int all)
804 {
805         struct btrfs_device *device;
806         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
807         unsigned long index;
808         int ret;
809         int i;
810         int j;
811         int cnt;
812 
813         spin_lock(&fs_info->reada_lock);
814         list_for_each_entry(device, &fs_devices->devices, dev_list) {
815                 btrfs_debug(fs_info, "dev %lld has %d in flight", device->devid,
816                         atomic_read(&device->reada_in_flight));
817                 index = 0;
818                 while (1) {
819                         struct reada_zone *zone;
820                         ret = radix_tree_gang_lookup(&device->reada_zones,
821                                                      (void **)&zone, index, 1);
822                         if (ret == 0)
823                                 break;
824                         pr_debug("  zone %llu-%llu elems %llu locked %d devs",
825                                     zone->start, zone->end, zone->elems,
826                                     zone->locked);
827                         for (j = 0; j < zone->ndevs; ++j) {
828                                 pr_cont(" %lld",
829                                         zone->devs[j]->devid);
830                         }
831                         if (device->reada_curr_zone == zone)
832                                 pr_cont(" curr off %llu",
833                                         device->reada_next - zone->start);
834                         pr_cont("\n");
835                         index = (zone->end >> PAGE_SHIFT) + 1;
836                 }
837                 cnt = 0;
838                 index = 0;
839                 while (all) {
840                         struct reada_extent *re = NULL;
841 
842                         ret = radix_tree_gang_lookup(&device->reada_extents,
843                                                      (void **)&re, index, 1);
844                         if (ret == 0)
845                                 break;
846                         pr_debug("  re: logical %llu size %u empty %d scheduled %d",
847                                 re->logical, fs_info->nodesize,
848                                 list_empty(&re->extctl), re->scheduled);
849 
850                         for (i = 0; i < re->nzones; ++i) {
851                                 pr_cont(" zone %llu-%llu devs",
852                                         re->zones[i]->start,
853                                         re->zones[i]->end);
854                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
855                                         pr_cont(" %lld",
856                                                 re->zones[i]->devs[j]->devid);
857                                 }
858                         }
859                         pr_cont("\n");
860                         index = (re->logical >> PAGE_SHIFT) + 1;
861                         if (++cnt > 15)
862                                 break;
863                 }
864         }
865 
866         index = 0;
867         cnt = 0;
868         while (all) {
869                 struct reada_extent *re = NULL;
870 
871                 ret = radix_tree_gang_lookup(&fs_info->reada_tree, (void **)&re,
872                                              index, 1);
873                 if (ret == 0)
874                         break;
875                 if (!re->scheduled) {
876                         index = (re->logical >> PAGE_SHIFT) + 1;
877                         continue;
878                 }
879                 pr_debug("re: logical %llu size %u list empty %d scheduled %d",
880                         re->logical, fs_info->nodesize,
881                         list_empty(&re->extctl), re->scheduled);
882                 for (i = 0; i < re->nzones; ++i) {
883                         pr_cont(" zone %llu-%llu devs",
884                                 re->zones[i]->start,
885                                 re->zones[i]->end);
886                         for (j = 0; j < re->zones[i]->ndevs; ++j) {
887                                 pr_cont(" %lld",
888                                        re->zones[i]->devs[j]->devid);
889                         }
890                 }
891                 pr_cont("\n");
892                 index = (re->logical >> PAGE_SHIFT) + 1;
893         }
894         spin_unlock(&fs_info->reada_lock);
895 }
896 #endif
897 
898 /*
899  * interface
900  */
901 struct reada_control *btrfs_reada_add(struct btrfs_root *root,
902                         struct btrfs_key *key_start, struct btrfs_key *key_end)
903 {
904         struct reada_control *rc;
905         u64 start;
906         u64 generation;
907         int ret;
908         struct extent_buffer *node;
909         static struct btrfs_key max_key = {
910                 .objectid = (u64)-1,
911                 .type = (u8)-1,
912                 .offset = (u64)-1
913         };
914 
915         rc = kzalloc(sizeof(*rc), GFP_KERNEL);
916         if (!rc)
917                 return ERR_PTR(-ENOMEM);
918 
919         rc->fs_info = root->fs_info;
920         rc->key_start = *key_start;
921         rc->key_end = *key_end;
922         atomic_set(&rc->elems, 0);
923         init_waitqueue_head(&rc->wait);
924         kref_init(&rc->refcnt);
925         kref_get(&rc->refcnt); /* one ref for having elements */
926 
927         node = btrfs_root_node(root);
928         start = node->start;
929         generation = btrfs_header_generation(node);
930         free_extent_buffer(node);
931 
932         ret = reada_add_block(rc, start, &max_key, generation);
933         if (ret) {
934                 kfree(rc);
935                 return ERR_PTR(ret);
936         }
937 
938         reada_start_machine(root->fs_info);
939 
940         return rc;
941 }
942 
943 #ifdef DEBUG
944 int btrfs_reada_wait(void *handle)
945 {
946         struct reada_control *rc = handle;
947         struct btrfs_fs_info *fs_info = rc->fs_info;
948 
949         while (atomic_read(&rc->elems)) {
950                 if (!atomic_read(&fs_info->reada_works_cnt))
951                         reada_start_machine(fs_info);
952                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
953                                    5 * HZ);
954                 dump_devs(fs_info, atomic_read(&rc->elems) < 10 ? 1 : 0);
955         }
956 
957         dump_devs(fs_info, atomic_read(&rc->elems) < 10 ? 1 : 0);
958 
959         kref_put(&rc->refcnt, reada_control_release);
960 
961         return 0;
962 }
963 #else
964 int btrfs_reada_wait(void *handle)
965 {
966         struct reada_control *rc = handle;
967         struct btrfs_fs_info *fs_info = rc->fs_info;
968 
969         while (atomic_read(&rc->elems)) {
970                 if (!atomic_read(&fs_info->reada_works_cnt))
971                         reada_start_machine(fs_info);
972                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
973                                    (HZ + 9) / 10);
974         }
975 
976         kref_put(&rc->refcnt, reada_control_release);
977 
978         return 0;
979 }
980 #endif
981 
982 void btrfs_reada_detach(void *handle)
983 {
984         struct reada_control *rc = handle;
985 
986         kref_put(&rc->refcnt, reada_control_release);
987 }
988 

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