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

Version: ~ [ linux-5.9 ] ~ [ linux-5.8.14 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.70 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.150 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.200 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.238 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.238 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.85 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
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  1 /*
  2  * Copyright (C) 2011 STRATO.  All rights reserved.
  3  *
  4  * This program is free software; you can redistribute it and/or
  5  * modify it under the terms of the GNU General Public
  6  * License v2 as published by the Free Software Foundation.
  7  *
  8  * This program is distributed in the hope that it will be useful,
  9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 11  * General Public License for more details.
 12  *
 13  * You should have received a copy of the GNU General Public
 14  * License along with this program; if not, write to the
 15  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 16  * Boston, MA 021110-1307, USA.
 17  */
 18 
 19 #include <linux/sched.h>
 20 #include <linux/pagemap.h>
 21 #include <linux/writeback.h>
 22 #include <linux/blkdev.h>
 23 #include <linux/rbtree.h>
 24 #include <linux/slab.h>
 25 #include <linux/workqueue.h>
 26 #include "ctree.h"
 27 #include "volumes.h"
 28 #include "disk-io.h"
 29 #include "transaction.h"
 30 #include "dev-replace.h"
 31 
 32 #undef DEBUG
 33 
 34 /*
 35  * This is the implementation for the generic read ahead framework.
 36  *
 37  * To trigger a readahead, btrfs_reada_add must be called. It will start
 38  * a read ahead for the given range [start, end) on tree root. The returned
 39  * handle can either be used to wait on the readahead to finish
 40  * (btrfs_reada_wait), or to send it to the background (btrfs_reada_detach).
 41  *
 42  * The read ahead works as follows:
 43  * On btrfs_reada_add, the root of the tree is inserted into a radix_tree.
 44  * reada_start_machine will then search for extents to prefetch and trigger
 45  * some reads. When a read finishes for a node, all contained node/leaf
 46  * pointers that lie in the given range will also be enqueued. The reads will
 47  * be triggered in sequential order, thus giving a big win over a naive
 48  * enumeration. It will also make use of multi-device layouts. Each disk
 49  * will have its on read pointer and all disks will by utilized in parallel.
 50  * Also will no two disks read both sides of a mirror simultaneously, as this
 51  * would waste seeking capacity. Instead both disks will read different parts
 52  * of the filesystem.
 53  * Any number of readaheads can be started in parallel. The read order will be
 54  * determined globally, i.e. 2 parallel readaheads will normally finish faster
 55  * than the 2 started one after another.
 56  */
 57 
 58 #define MAX_IN_FLIGHT 6
 59 
 60 struct reada_extctl {
 61         struct list_head        list;
 62         struct reada_control    *rc;
 63         u64                     generation;
 64 };
 65 
 66 struct reada_extent {
 67         u64                     logical;
 68         struct btrfs_key        top;
 69         u32                     blocksize;
 70         int                     err;
 71         struct list_head        extctl;
 72         int                     refcnt;
 73         spinlock_t              lock;
 74         struct reada_zone       *zones[BTRFS_MAX_MIRRORS];
 75         int                     nzones;
 76         struct btrfs_device     *scheduled_for;
 77 };
 78 
 79 struct reada_zone {
 80         u64                     start;
 81         u64                     end;
 82         u64                     elems;
 83         struct list_head        list;
 84         spinlock_t              lock;
 85         int                     locked;
 86         struct btrfs_device     *device;
 87         struct btrfs_device     *devs[BTRFS_MAX_MIRRORS]; /* full list, incl
 88                                                            * self */
 89         int                     ndevs;
 90         struct kref             refcnt;
 91 };
 92 
 93 struct reada_machine_work {
 94         struct btrfs_work       work;
 95         struct btrfs_fs_info    *fs_info;
 96 };
 97 
 98 static void reada_extent_put(struct btrfs_fs_info *, struct reada_extent *);
 99 static void reada_control_release(struct kref *kref);
100 static void reada_zone_release(struct kref *kref);
101 static void reada_start_machine(struct btrfs_fs_info *fs_info);
102 static void __reada_start_machine(struct btrfs_fs_info *fs_info);
103 
104 static int reada_add_block(struct reada_control *rc, u64 logical,
105                            struct btrfs_key *top, int level, u64 generation);
106 
107 /* recurses */
108 /* in case of err, eb might be NULL */
109 static int __readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
110                             u64 start, int err)
111 {
112         int level = 0;
113         int nritems;
114         int i;
115         u64 bytenr;
116         u64 generation;
117         struct reada_extent *re;
118         struct btrfs_fs_info *fs_info = root->fs_info;
119         struct list_head list;
120         unsigned long index = start >> PAGE_CACHE_SHIFT;
121         struct btrfs_device *for_dev;
122 
123         if (eb)
124                 level = btrfs_header_level(eb);
125 
126         /* find extent */
127         spin_lock(&fs_info->reada_lock);
128         re = radix_tree_lookup(&fs_info->reada_tree, index);
129         if (re)
130                 re->refcnt++;
131         spin_unlock(&fs_info->reada_lock);
132 
133         if (!re)
134                 return -1;
135 
136         spin_lock(&re->lock);
137         /*
138          * just take the full list from the extent. afterwards we
139          * don't need the lock anymore
140          */
141         list_replace_init(&re->extctl, &list);
142         for_dev = re->scheduled_for;
143         re->scheduled_for = NULL;
144         spin_unlock(&re->lock);
145 
146         if (err == 0) {
147                 nritems = level ? btrfs_header_nritems(eb) : 0;
148                 generation = btrfs_header_generation(eb);
149                 /*
150                  * FIXME: currently we just set nritems to 0 if this is a leaf,
151                  * effectively ignoring the content. In a next step we could
152                  * trigger more readahead depending from the content, e.g.
153                  * fetch the checksums for the extents in the leaf.
154                  */
155         } else {
156                 /*
157                  * this is the error case, the extent buffer has not been
158                  * read correctly. We won't access anything from it and
159                  * just cleanup our data structures. Effectively this will
160                  * cut the branch below this node from read ahead.
161                  */
162                 nritems = 0;
163                 generation = 0;
164         }
165 
166         for (i = 0; i < nritems; i++) {
167                 struct reada_extctl *rec;
168                 u64 n_gen;
169                 struct btrfs_key key;
170                 struct btrfs_key next_key;
171 
172                 btrfs_node_key_to_cpu(eb, &key, i);
173                 if (i + 1 < nritems)
174                         btrfs_node_key_to_cpu(eb, &next_key, i + 1);
175                 else
176                         next_key = re->top;
177                 bytenr = btrfs_node_blockptr(eb, i);
178                 n_gen = btrfs_node_ptr_generation(eb, i);
179 
180                 list_for_each_entry(rec, &list, list) {
181                         struct reada_control *rc = rec->rc;
182 
183                         /*
184                          * if the generation doesn't match, just ignore this
185                          * extctl. This will probably cut off a branch from
186                          * prefetch. Alternatively one could start a new (sub-)
187                          * prefetch for this branch, starting again from root.
188                          * FIXME: move the generation check out of this loop
189                          */
190 #ifdef DEBUG
191                         if (rec->generation != generation) {
192                                 btrfs_debug(root->fs_info,
193                                            "generation mismatch for (%llu,%d,%llu) %llu != %llu",
194                                        key.objectid, key.type, key.offset,
195                                        rec->generation, generation);
196                         }
197 #endif
198                         if (rec->generation == generation &&
199                             btrfs_comp_cpu_keys(&key, &rc->key_end) < 0 &&
200                             btrfs_comp_cpu_keys(&next_key, &rc->key_start) > 0)
201                                 reada_add_block(rc, bytenr, &next_key,
202                                                 level - 1, n_gen);
203                 }
204         }
205         /*
206          * free extctl records
207          */
208         while (!list_empty(&list)) {
209                 struct reada_control *rc;
210                 struct reada_extctl *rec;
211 
212                 rec = list_first_entry(&list, struct reada_extctl, list);
213                 list_del(&rec->list);
214                 rc = rec->rc;
215                 kfree(rec);
216 
217                 kref_get(&rc->refcnt);
218                 if (atomic_dec_and_test(&rc->elems)) {
219                         kref_put(&rc->refcnt, reada_control_release);
220                         wake_up(&rc->wait);
221                 }
222                 kref_put(&rc->refcnt, reada_control_release);
223 
224                 reada_extent_put(fs_info, re);  /* one ref for each entry */
225         }
226         reada_extent_put(fs_info, re);  /* our ref */
227         if (for_dev)
228                 atomic_dec(&for_dev->reada_in_flight);
229 
230         return 0;
231 }
232 
233 /*
234  * start is passed separately in case eb in NULL, which may be the case with
235  * failed I/O
236  */
237 int btree_readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
238                          u64 start, int err)
239 {
240         int ret;
241 
242         ret = __readahead_hook(root, eb, start, err);
243 
244         reada_start_machine(root->fs_info);
245 
246         return ret;
247 }
248 
249 static struct reada_zone *reada_find_zone(struct btrfs_fs_info *fs_info,
250                                           struct btrfs_device *dev, u64 logical,
251                                           struct btrfs_bio *bbio)
252 {
253         int ret;
254         struct reada_zone *zone;
255         struct btrfs_block_group_cache *cache = NULL;
256         u64 start;
257         u64 end;
258         int i;
259 
260         zone = NULL;
261         spin_lock(&fs_info->reada_lock);
262         ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
263                                      logical >> PAGE_CACHE_SHIFT, 1);
264         if (ret == 1)
265                 kref_get(&zone->refcnt);
266         spin_unlock(&fs_info->reada_lock);
267 
268         if (ret == 1) {
269                 if (logical >= zone->start && logical < zone->end)
270                         return zone;
271                 spin_lock(&fs_info->reada_lock);
272                 kref_put(&zone->refcnt, reada_zone_release);
273                 spin_unlock(&fs_info->reada_lock);
274         }
275 
276         cache = btrfs_lookup_block_group(fs_info, logical);
277         if (!cache)
278                 return NULL;
279 
280         start = cache->key.objectid;
281         end = start + cache->key.offset - 1;
282         btrfs_put_block_group(cache);
283 
284         zone = kzalloc(sizeof(*zone), GFP_NOFS);
285         if (!zone)
286                 return NULL;
287 
288         zone->start = start;
289         zone->end = end;
290         INIT_LIST_HEAD(&zone->list);
291         spin_lock_init(&zone->lock);
292         zone->locked = 0;
293         kref_init(&zone->refcnt);
294         zone->elems = 0;
295         zone->device = dev; /* our device always sits at index 0 */
296         for (i = 0; i < bbio->num_stripes; ++i) {
297                 /* bounds have already been checked */
298                 zone->devs[i] = bbio->stripes[i].dev;
299         }
300         zone->ndevs = bbio->num_stripes;
301 
302         spin_lock(&fs_info->reada_lock);
303         ret = radix_tree_insert(&dev->reada_zones,
304                                 (unsigned long)(zone->end >> PAGE_CACHE_SHIFT),
305                                 zone);
306 
307         if (ret == -EEXIST) {
308                 kfree(zone);
309                 ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
310                                              logical >> PAGE_CACHE_SHIFT, 1);
311                 if (ret == 1)
312                         kref_get(&zone->refcnt);
313         }
314         spin_unlock(&fs_info->reada_lock);
315 
316         return zone;
317 }
318 
319 static struct reada_extent *reada_find_extent(struct btrfs_root *root,
320                                               u64 logical,
321                                               struct btrfs_key *top, int level)
322 {
323         int ret;
324         struct reada_extent *re = NULL;
325         struct reada_extent *re_exist = NULL;
326         struct btrfs_fs_info *fs_info = root->fs_info;
327         struct btrfs_bio *bbio = NULL;
328         struct btrfs_device *dev;
329         struct btrfs_device *prev_dev;
330         u32 blocksize;
331         u64 length;
332         int nzones = 0;
333         int i;
334         unsigned long index = logical >> PAGE_CACHE_SHIFT;
335         int dev_replace_is_ongoing;
336 
337         spin_lock(&fs_info->reada_lock);
338         re = radix_tree_lookup(&fs_info->reada_tree, index);
339         if (re)
340                 re->refcnt++;
341         spin_unlock(&fs_info->reada_lock);
342 
343         if (re)
344                 return re;
345 
346         re = kzalloc(sizeof(*re), GFP_NOFS);
347         if (!re)
348                 return NULL;
349 
350         blocksize = btrfs_level_size(root, level);
351         re->logical = logical;
352         re->blocksize = blocksize;
353         re->top = *top;
354         INIT_LIST_HEAD(&re->extctl);
355         spin_lock_init(&re->lock);
356         re->refcnt = 1;
357 
358         /*
359          * map block
360          */
361         length = blocksize;
362         ret = btrfs_map_block(fs_info, REQ_GET_READ_MIRRORS, logical, &length,
363                               &bbio, 0);
364         if (ret || !bbio || length < blocksize)
365                 goto error;
366 
367         if (bbio->num_stripes > BTRFS_MAX_MIRRORS) {
368                 btrfs_err(root->fs_info,
369                            "readahead: more than %d copies not supported",
370                            BTRFS_MAX_MIRRORS);
371                 goto error;
372         }
373 
374         for (nzones = 0; nzones < bbio->num_stripes; ++nzones) {
375                 struct reada_zone *zone;
376 
377                 dev = bbio->stripes[nzones].dev;
378                 zone = reada_find_zone(fs_info, dev, logical, bbio);
379                 if (!zone)
380                         break;
381 
382                 re->zones[nzones] = zone;
383                 spin_lock(&zone->lock);
384                 if (!zone->elems)
385                         kref_get(&zone->refcnt);
386                 ++zone->elems;
387                 spin_unlock(&zone->lock);
388                 spin_lock(&fs_info->reada_lock);
389                 kref_put(&zone->refcnt, reada_zone_release);
390                 spin_unlock(&fs_info->reada_lock);
391         }
392         re->nzones = nzones;
393         if (nzones == 0) {
394                 /* not a single zone found, error and out */
395                 goto error;
396         }
397 
398         /* insert extent in reada_tree + all per-device trees, all or nothing */
399         btrfs_dev_replace_lock(&fs_info->dev_replace);
400         spin_lock(&fs_info->reada_lock);
401         ret = radix_tree_insert(&fs_info->reada_tree, index, re);
402         if (ret == -EEXIST) {
403                 re_exist = radix_tree_lookup(&fs_info->reada_tree, index);
404                 BUG_ON(!re_exist);
405                 re_exist->refcnt++;
406                 spin_unlock(&fs_info->reada_lock);
407                 btrfs_dev_replace_unlock(&fs_info->dev_replace);
408                 goto error;
409         }
410         if (ret) {
411                 spin_unlock(&fs_info->reada_lock);
412                 btrfs_dev_replace_unlock(&fs_info->dev_replace);
413                 goto error;
414         }
415         prev_dev = NULL;
416         dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(
417                         &fs_info->dev_replace);
418         for (i = 0; i < nzones; ++i) {
419                 dev = bbio->stripes[i].dev;
420                 if (dev == prev_dev) {
421                         /*
422                          * in case of DUP, just add the first zone. As both
423                          * are on the same device, there's nothing to gain
424                          * from adding both.
425                          * Also, it wouldn't work, as the tree is per device
426                          * and adding would fail with EEXIST
427                          */
428                         continue;
429                 }
430                 if (!dev->bdev) {
431                         /* cannot read ahead on missing device */
432                         continue;
433                 }
434                 if (dev_replace_is_ongoing &&
435                     dev == fs_info->dev_replace.tgtdev) {
436                         /*
437                          * as this device is selected for reading only as
438                          * a last resort, skip it for read ahead.
439                          */
440                         continue;
441                 }
442                 prev_dev = dev;
443                 ret = radix_tree_insert(&dev->reada_extents, index, re);
444                 if (ret) {
445                         while (--i >= 0) {
446                                 dev = bbio->stripes[i].dev;
447                                 BUG_ON(dev == NULL);
448                                 /* ignore whether the entry was inserted */
449                                 radix_tree_delete(&dev->reada_extents, index);
450                         }
451                         BUG_ON(fs_info == NULL);
452                         radix_tree_delete(&fs_info->reada_tree, index);
453                         spin_unlock(&fs_info->reada_lock);
454                         btrfs_dev_replace_unlock(&fs_info->dev_replace);
455                         goto error;
456                 }
457         }
458         spin_unlock(&fs_info->reada_lock);
459         btrfs_dev_replace_unlock(&fs_info->dev_replace);
460 
461         kfree(bbio);
462         return re;
463 
464 error:
465         while (nzones) {
466                 struct reada_zone *zone;
467 
468                 --nzones;
469                 zone = re->zones[nzones];
470                 kref_get(&zone->refcnt);
471                 spin_lock(&zone->lock);
472                 --zone->elems;
473                 if (zone->elems == 0) {
474                         /*
475                          * no fs_info->reada_lock needed, as this can't be
476                          * the last ref
477                          */
478                         kref_put(&zone->refcnt, reada_zone_release);
479                 }
480                 spin_unlock(&zone->lock);
481 
482                 spin_lock(&fs_info->reada_lock);
483                 kref_put(&zone->refcnt, reada_zone_release);
484                 spin_unlock(&fs_info->reada_lock);
485         }
486         kfree(bbio);
487         kfree(re);
488         return re_exist;
489 }
490 
491 static void reada_extent_put(struct btrfs_fs_info *fs_info,
492                              struct reada_extent *re)
493 {
494         int i;
495         unsigned long index = re->logical >> PAGE_CACHE_SHIFT;
496 
497         spin_lock(&fs_info->reada_lock);
498         if (--re->refcnt) {
499                 spin_unlock(&fs_info->reada_lock);
500                 return;
501         }
502 
503         radix_tree_delete(&fs_info->reada_tree, index);
504         for (i = 0; i < re->nzones; ++i) {
505                 struct reada_zone *zone = re->zones[i];
506 
507                 radix_tree_delete(&zone->device->reada_extents, index);
508         }
509 
510         spin_unlock(&fs_info->reada_lock);
511 
512         for (i = 0; i < re->nzones; ++i) {
513                 struct reada_zone *zone = re->zones[i];
514 
515                 kref_get(&zone->refcnt);
516                 spin_lock(&zone->lock);
517                 --zone->elems;
518                 if (zone->elems == 0) {
519                         /* no fs_info->reada_lock needed, as this can't be
520                          * the last ref */
521                         kref_put(&zone->refcnt, reada_zone_release);
522                 }
523                 spin_unlock(&zone->lock);
524 
525                 spin_lock(&fs_info->reada_lock);
526                 kref_put(&zone->refcnt, reada_zone_release);
527                 spin_unlock(&fs_info->reada_lock);
528         }
529         if (re->scheduled_for)
530                 atomic_dec(&re->scheduled_for->reada_in_flight);
531 
532         kfree(re);
533 }
534 
535 static void reada_zone_release(struct kref *kref)
536 {
537         struct reada_zone *zone = container_of(kref, struct reada_zone, refcnt);
538 
539         radix_tree_delete(&zone->device->reada_zones,
540                           zone->end >> PAGE_CACHE_SHIFT);
541 
542         kfree(zone);
543 }
544 
545 static void reada_control_release(struct kref *kref)
546 {
547         struct reada_control *rc = container_of(kref, struct reada_control,
548                                                 refcnt);
549 
550         kfree(rc);
551 }
552 
553 static int reada_add_block(struct reada_control *rc, u64 logical,
554                            struct btrfs_key *top, int level, u64 generation)
555 {
556         struct btrfs_root *root = rc->root;
557         struct reada_extent *re;
558         struct reada_extctl *rec;
559 
560         re = reada_find_extent(root, logical, top, level); /* takes one ref */
561         if (!re)
562                 return -1;
563 
564         rec = kzalloc(sizeof(*rec), GFP_NOFS);
565         if (!rec) {
566                 reada_extent_put(root->fs_info, re);
567                 return -1;
568         }
569 
570         rec->rc = rc;
571         rec->generation = generation;
572         atomic_inc(&rc->elems);
573 
574         spin_lock(&re->lock);
575         list_add_tail(&rec->list, &re->extctl);
576         spin_unlock(&re->lock);
577 
578         /* leave the ref on the extent */
579 
580         return 0;
581 }
582 
583 /*
584  * called with fs_info->reada_lock held
585  */
586 static void reada_peer_zones_set_lock(struct reada_zone *zone, int lock)
587 {
588         int i;
589         unsigned long index = zone->end >> PAGE_CACHE_SHIFT;
590 
591         for (i = 0; i < zone->ndevs; ++i) {
592                 struct reada_zone *peer;
593                 peer = radix_tree_lookup(&zone->devs[i]->reada_zones, index);
594                 if (peer && peer->device != zone->device)
595                         peer->locked = lock;
596         }
597 }
598 
599 /*
600  * called with fs_info->reada_lock held
601  */
602 static int reada_pick_zone(struct btrfs_device *dev)
603 {
604         struct reada_zone *top_zone = NULL;
605         struct reada_zone *top_locked_zone = NULL;
606         u64 top_elems = 0;
607         u64 top_locked_elems = 0;
608         unsigned long index = 0;
609         int ret;
610 
611         if (dev->reada_curr_zone) {
612                 reada_peer_zones_set_lock(dev->reada_curr_zone, 0);
613                 kref_put(&dev->reada_curr_zone->refcnt, reada_zone_release);
614                 dev->reada_curr_zone = NULL;
615         }
616         /* pick the zone with the most elements */
617         while (1) {
618                 struct reada_zone *zone;
619 
620                 ret = radix_tree_gang_lookup(&dev->reada_zones,
621                                              (void **)&zone, index, 1);
622                 if (ret == 0)
623                         break;
624                 index = (zone->end >> PAGE_CACHE_SHIFT) + 1;
625                 if (zone->locked) {
626                         if (zone->elems > top_locked_elems) {
627                                 top_locked_elems = zone->elems;
628                                 top_locked_zone = zone;
629                         }
630                 } else {
631                         if (zone->elems > top_elems) {
632                                 top_elems = zone->elems;
633                                 top_zone = zone;
634                         }
635                 }
636         }
637         if (top_zone)
638                 dev->reada_curr_zone = top_zone;
639         else if (top_locked_zone)
640                 dev->reada_curr_zone = top_locked_zone;
641         else
642                 return 0;
643 
644         dev->reada_next = dev->reada_curr_zone->start;
645         kref_get(&dev->reada_curr_zone->refcnt);
646         reada_peer_zones_set_lock(dev->reada_curr_zone, 1);
647 
648         return 1;
649 }
650 
651 static int reada_start_machine_dev(struct btrfs_fs_info *fs_info,
652                                    struct btrfs_device *dev)
653 {
654         struct reada_extent *re = NULL;
655         int mirror_num = 0;
656         struct extent_buffer *eb = NULL;
657         u64 logical;
658         u32 blocksize;
659         int ret;
660         int i;
661         int need_kick = 0;
662 
663         spin_lock(&fs_info->reada_lock);
664         if (dev->reada_curr_zone == NULL) {
665                 ret = reada_pick_zone(dev);
666                 if (!ret) {
667                         spin_unlock(&fs_info->reada_lock);
668                         return 0;
669                 }
670         }
671         /*
672          * FIXME currently we issue the reads one extent at a time. If we have
673          * a contiguous block of extents, we could also coagulate them or use
674          * plugging to speed things up
675          */
676         ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
677                                      dev->reada_next >> PAGE_CACHE_SHIFT, 1);
678         if (ret == 0 || re->logical >= dev->reada_curr_zone->end) {
679                 ret = reada_pick_zone(dev);
680                 if (!ret) {
681                         spin_unlock(&fs_info->reada_lock);
682                         return 0;
683                 }
684                 re = NULL;
685                 ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
686                                         dev->reada_next >> PAGE_CACHE_SHIFT, 1);
687         }
688         if (ret == 0) {
689                 spin_unlock(&fs_info->reada_lock);
690                 return 0;
691         }
692         dev->reada_next = re->logical + re->blocksize;
693         re->refcnt++;
694 
695         spin_unlock(&fs_info->reada_lock);
696 
697         /*
698          * find mirror num
699          */
700         for (i = 0; i < re->nzones; ++i) {
701                 if (re->zones[i]->device == dev) {
702                         mirror_num = i + 1;
703                         break;
704                 }
705         }
706         logical = re->logical;
707         blocksize = re->blocksize;
708 
709         spin_lock(&re->lock);
710         if (re->scheduled_for == NULL) {
711                 re->scheduled_for = dev;
712                 need_kick = 1;
713         }
714         spin_unlock(&re->lock);
715 
716         reada_extent_put(fs_info, re);
717 
718         if (!need_kick)
719                 return 0;
720 
721         atomic_inc(&dev->reada_in_flight);
722         ret = reada_tree_block_flagged(fs_info->extent_root, logical, blocksize,
723                          mirror_num, &eb);
724         if (ret)
725                 __readahead_hook(fs_info->extent_root, NULL, logical, ret);
726         else if (eb)
727                 __readahead_hook(fs_info->extent_root, eb, eb->start, ret);
728 
729         if (eb)
730                 free_extent_buffer(eb);
731 
732         return 1;
733 
734 }
735 
736 static void reada_start_machine_worker(struct btrfs_work *work)
737 {
738         struct reada_machine_work *rmw;
739         struct btrfs_fs_info *fs_info;
740         int old_ioprio;
741 
742         rmw = container_of(work, struct reada_machine_work, work);
743         fs_info = rmw->fs_info;
744 
745         kfree(rmw);
746 
747         old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
748                                        task_nice_ioprio(current));
749         set_task_ioprio(current, BTRFS_IOPRIO_READA);
750         __reada_start_machine(fs_info);
751         set_task_ioprio(current, old_ioprio);
752 }
753 
754 static void __reada_start_machine(struct btrfs_fs_info *fs_info)
755 {
756         struct btrfs_device *device;
757         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
758         u64 enqueued;
759         u64 total = 0;
760         int i;
761 
762         do {
763                 enqueued = 0;
764                 list_for_each_entry(device, &fs_devices->devices, dev_list) {
765                         if (atomic_read(&device->reada_in_flight) <
766                             MAX_IN_FLIGHT)
767                                 enqueued += reada_start_machine_dev(fs_info,
768                                                                     device);
769                 }
770                 total += enqueued;
771         } while (enqueued && total < 10000);
772 
773         if (enqueued == 0)
774                 return;
775 
776         /*
777          * If everything is already in the cache, this is effectively single
778          * threaded. To a) not hold the caller for too long and b) to utilize
779          * more cores, we broke the loop above after 10000 iterations and now
780          * enqueue to workers to finish it. This will distribute the load to
781          * the cores.
782          */
783         for (i = 0; i < 2; ++i)
784                 reada_start_machine(fs_info);
785 }
786 
787 static void reada_start_machine(struct btrfs_fs_info *fs_info)
788 {
789         struct reada_machine_work *rmw;
790 
791         rmw = kzalloc(sizeof(*rmw), GFP_NOFS);
792         if (!rmw) {
793                 /* FIXME we cannot handle this properly right now */
794                 BUG();
795         }
796         btrfs_init_work(&rmw->work, reada_start_machine_worker, NULL, NULL);
797         rmw->fs_info = fs_info;
798 
799         btrfs_queue_work(fs_info->readahead_workers, &rmw->work);
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                 printk(KERN_DEBUG "dev %lld has %d in flight\n", 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                         printk(KERN_DEBUG "  zone %llu-%llu elems %llu locked "
825                                 "%d devs", zone->start, zone->end, zone->elems,
826                                 zone->locked);
827                         for (j = 0; j < zone->ndevs; ++j) {
828                                 printk(KERN_CONT " %lld",
829                                         zone->devs[j]->devid);
830                         }
831                         if (device->reada_curr_zone == zone)
832                                 printk(KERN_CONT " curr off %llu",
833                                         device->reada_next - zone->start);
834                         printk(KERN_CONT "\n");
835                         index = (zone->end >> PAGE_CACHE_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                         printk(KERN_DEBUG
847                                 "  re: logical %llu size %u empty %d for %lld",
848                                 re->logical, re->blocksize,
849                                 list_empty(&re->extctl), re->scheduled_for ?
850                                 re->scheduled_for->devid : -1);
851 
852                         for (i = 0; i < re->nzones; ++i) {
853                                 printk(KERN_CONT " zone %llu-%llu devs",
854                                         re->zones[i]->start,
855                                         re->zones[i]->end);
856                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
857                                         printk(KERN_CONT " %lld",
858                                                 re->zones[i]->devs[j]->devid);
859                                 }
860                         }
861                         printk(KERN_CONT "\n");
862                         index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
863                         if (++cnt > 15)
864                                 break;
865                 }
866         }
867 
868         index = 0;
869         cnt = 0;
870         while (all) {
871                 struct reada_extent *re = NULL;
872 
873                 ret = radix_tree_gang_lookup(&fs_info->reada_tree, (void **)&re,
874                                              index, 1);
875                 if (ret == 0)
876                         break;
877                 if (!re->scheduled_for) {
878                         index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
879                         continue;
880                 }
881                 printk(KERN_DEBUG
882                         "re: logical %llu size %u list empty %d for %lld",
883                         re->logical, re->blocksize, list_empty(&re->extctl),
884                         re->scheduled_for ? re->scheduled_for->devid : -1);
885                 for (i = 0; i < re->nzones; ++i) {
886                         printk(KERN_CONT " zone %llu-%llu devs",
887                                 re->zones[i]->start,
888                                 re->zones[i]->end);
889                         for (i = 0; i < re->nzones; ++i) {
890                                 printk(KERN_CONT " zone %llu-%llu devs",
891                                         re->zones[i]->start,
892                                         re->zones[i]->end);
893                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
894                                         printk(KERN_CONT " %lld",
895                                                 re->zones[i]->devs[j]->devid);
896                                 }
897                         }
898                 }
899                 printk(KERN_CONT "\n");
900                 index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
901         }
902         spin_unlock(&fs_info->reada_lock);
903 }
904 #endif
905 
906 /*
907  * interface
908  */
909 struct reada_control *btrfs_reada_add(struct btrfs_root *root,
910                         struct btrfs_key *key_start, struct btrfs_key *key_end)
911 {
912         struct reada_control *rc;
913         u64 start;
914         u64 generation;
915         int level;
916         struct extent_buffer *node;
917         static struct btrfs_key max_key = {
918                 .objectid = (u64)-1,
919                 .type = (u8)-1,
920                 .offset = (u64)-1
921         };
922 
923         rc = kzalloc(sizeof(*rc), GFP_NOFS);
924         if (!rc)
925                 return ERR_PTR(-ENOMEM);
926 
927         rc->root = root;
928         rc->key_start = *key_start;
929         rc->key_end = *key_end;
930         atomic_set(&rc->elems, 0);
931         init_waitqueue_head(&rc->wait);
932         kref_init(&rc->refcnt);
933         kref_get(&rc->refcnt); /* one ref for having elements */
934 
935         node = btrfs_root_node(root);
936         start = node->start;
937         level = btrfs_header_level(node);
938         generation = btrfs_header_generation(node);
939         free_extent_buffer(node);
940 
941         if (reada_add_block(rc, start, &max_key, level, generation)) {
942                 kfree(rc);
943                 return ERR_PTR(-ENOMEM);
944         }
945 
946         reada_start_machine(root->fs_info);
947 
948         return rc;
949 }
950 
951 #ifdef DEBUG
952 int btrfs_reada_wait(void *handle)
953 {
954         struct reada_control *rc = handle;
955 
956         while (atomic_read(&rc->elems)) {
957                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
958                                    5 * HZ);
959                 dump_devs(rc->root->fs_info,
960                           atomic_read(&rc->elems) < 10 ? 1 : 0);
961         }
962 
963         dump_devs(rc->root->fs_info, atomic_read(&rc->elems) < 10 ? 1 : 0);
964 
965         kref_put(&rc->refcnt, reada_control_release);
966 
967         return 0;
968 }
969 #else
970 int btrfs_reada_wait(void *handle)
971 {
972         struct reada_control *rc = handle;
973 
974         while (atomic_read(&rc->elems)) {
975                 wait_event(rc->wait, atomic_read(&rc->elems) == 0);
976         }
977 
978         kref_put(&rc->refcnt, reada_control_release);
979 
980         return 0;
981 }
982 #endif
983 
984 void btrfs_reada_detach(void *handle)
985 {
986         struct reada_control *rc = handle;
987 
988         kref_put(&rc->refcnt, reada_control_release);
989 }
990 

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