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

Version: ~ [ linux-5.5-rc7 ] ~ [ linux-5.4.13 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.97 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.166 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.210 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.210 ] ~ [ 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-3.16.81 ] ~ [ 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-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ 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 // 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         ret = radix_tree_preload(GFP_KERNEL);
380         if (ret)
381                 goto error;
382 
383         /* insert extent in reada_tree + all per-device trees, all or nothing */
384         btrfs_dev_replace_read_lock(&fs_info->dev_replace);
385         spin_lock(&fs_info->reada_lock);
386         ret = radix_tree_insert(&fs_info->reada_tree, index, re);
387         if (ret == -EEXIST) {
388                 re_exist = radix_tree_lookup(&fs_info->reada_tree, index);
389                 re_exist->refcnt++;
390                 spin_unlock(&fs_info->reada_lock);
391                 btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
392                 radix_tree_preload_end();
393                 goto error;
394         }
395         if (ret) {
396                 spin_unlock(&fs_info->reada_lock);
397                 btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
398                 radix_tree_preload_end();
399                 goto error;
400         }
401         radix_tree_preload_end();
402         prev_dev = NULL;
403         dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(
404                         &fs_info->dev_replace);
405         for (nzones = 0; nzones < re->nzones; ++nzones) {
406                 dev = re->zones[nzones]->device;
407 
408                 if (dev == prev_dev) {
409                         /*
410                          * in case of DUP, just add the first zone. As both
411                          * are on the same device, there's nothing to gain
412                          * from adding both.
413                          * Also, it wouldn't work, as the tree is per device
414                          * and adding would fail with EEXIST
415                          */
416                         continue;
417                 }
418                 if (!dev->bdev)
419                         continue;
420 
421                 if (dev_replace_is_ongoing &&
422                     dev == fs_info->dev_replace.tgtdev) {
423                         /*
424                          * as this device is selected for reading only as
425                          * a last resort, skip it for read ahead.
426                          */
427                         continue;
428                 }
429                 prev_dev = dev;
430                 ret = radix_tree_insert(&dev->reada_extents, index, re);
431                 if (ret) {
432                         while (--nzones >= 0) {
433                                 dev = re->zones[nzones]->device;
434                                 BUG_ON(dev == NULL);
435                                 /* ignore whether the entry was inserted */
436                                 radix_tree_delete(&dev->reada_extents, index);
437                         }
438                         radix_tree_delete(&fs_info->reada_tree, index);
439                         spin_unlock(&fs_info->reada_lock);
440                         btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
441                         goto error;
442                 }
443                 have_zone = 1;
444         }
445         spin_unlock(&fs_info->reada_lock);
446         btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
447 
448         if (!have_zone)
449                 goto error;
450 
451         btrfs_put_bbio(bbio);
452         return re;
453 
454 error:
455         for (nzones = 0; nzones < re->nzones; ++nzones) {
456                 struct reada_zone *zone;
457 
458                 zone = re->zones[nzones];
459                 kref_get(&zone->refcnt);
460                 spin_lock(&zone->lock);
461                 --zone->elems;
462                 if (zone->elems == 0) {
463                         /*
464                          * no fs_info->reada_lock needed, as this can't be
465                          * the last ref
466                          */
467                         kref_put(&zone->refcnt, reada_zone_release);
468                 }
469                 spin_unlock(&zone->lock);
470 
471                 spin_lock(&fs_info->reada_lock);
472                 kref_put(&zone->refcnt, reada_zone_release);
473                 spin_unlock(&fs_info->reada_lock);
474         }
475         btrfs_put_bbio(bbio);
476         kfree(re);
477         return re_exist;
478 }
479 
480 static void reada_extent_put(struct btrfs_fs_info *fs_info,
481                              struct reada_extent *re)
482 {
483         int i;
484         unsigned long index = re->logical >> PAGE_SHIFT;
485 
486         spin_lock(&fs_info->reada_lock);
487         if (--re->refcnt) {
488                 spin_unlock(&fs_info->reada_lock);
489                 return;
490         }
491 
492         radix_tree_delete(&fs_info->reada_tree, index);
493         for (i = 0; i < re->nzones; ++i) {
494                 struct reada_zone *zone = re->zones[i];
495 
496                 radix_tree_delete(&zone->device->reada_extents, index);
497         }
498 
499         spin_unlock(&fs_info->reada_lock);
500 
501         for (i = 0; i < re->nzones; ++i) {
502                 struct reada_zone *zone = re->zones[i];
503 
504                 kref_get(&zone->refcnt);
505                 spin_lock(&zone->lock);
506                 --zone->elems;
507                 if (zone->elems == 0) {
508                         /* no fs_info->reada_lock needed, as this can't be
509                          * the last ref */
510                         kref_put(&zone->refcnt, reada_zone_release);
511                 }
512                 spin_unlock(&zone->lock);
513 
514                 spin_lock(&fs_info->reada_lock);
515                 kref_put(&zone->refcnt, reada_zone_release);
516                 spin_unlock(&fs_info->reada_lock);
517         }
518 
519         kfree(re);
520 }
521 
522 static void reada_zone_release(struct kref *kref)
523 {
524         struct reada_zone *zone = container_of(kref, struct reada_zone, refcnt);
525 
526         radix_tree_delete(&zone->device->reada_zones,
527                           zone->end >> PAGE_SHIFT);
528 
529         kfree(zone);
530 }
531 
532 static void reada_control_release(struct kref *kref)
533 {
534         struct reada_control *rc = container_of(kref, struct reada_control,
535                                                 refcnt);
536 
537         kfree(rc);
538 }
539 
540 static int reada_add_block(struct reada_control *rc, u64 logical,
541                            struct btrfs_key *top, u64 generation)
542 {
543         struct btrfs_fs_info *fs_info = rc->fs_info;
544         struct reada_extent *re;
545         struct reada_extctl *rec;
546 
547         /* takes one ref */
548         re = reada_find_extent(fs_info, logical, top);
549         if (!re)
550                 return -1;
551 
552         rec = kzalloc(sizeof(*rec), GFP_KERNEL);
553         if (!rec) {
554                 reada_extent_put(fs_info, re);
555                 return -ENOMEM;
556         }
557 
558         rec->rc = rc;
559         rec->generation = generation;
560         atomic_inc(&rc->elems);
561 
562         spin_lock(&re->lock);
563         list_add_tail(&rec->list, &re->extctl);
564         spin_unlock(&re->lock);
565 
566         /* leave the ref on the extent */
567 
568         return 0;
569 }
570 
571 /*
572  * called with fs_info->reada_lock held
573  */
574 static void reada_peer_zones_set_lock(struct reada_zone *zone, int lock)
575 {
576         int i;
577         unsigned long index = zone->end >> PAGE_SHIFT;
578 
579         for (i = 0; i < zone->ndevs; ++i) {
580                 struct reada_zone *peer;
581                 peer = radix_tree_lookup(&zone->devs[i]->reada_zones, index);
582                 if (peer && peer->device != zone->device)
583                         peer->locked = lock;
584         }
585 }
586 
587 /*
588  * called with fs_info->reada_lock held
589  */
590 static int reada_pick_zone(struct btrfs_device *dev)
591 {
592         struct reada_zone *top_zone = NULL;
593         struct reada_zone *top_locked_zone = NULL;
594         u64 top_elems = 0;
595         u64 top_locked_elems = 0;
596         unsigned long index = 0;
597         int ret;
598 
599         if (dev->reada_curr_zone) {
600                 reada_peer_zones_set_lock(dev->reada_curr_zone, 0);
601                 kref_put(&dev->reada_curr_zone->refcnt, reada_zone_release);
602                 dev->reada_curr_zone = NULL;
603         }
604         /* pick the zone with the most elements */
605         while (1) {
606                 struct reada_zone *zone;
607 
608                 ret = radix_tree_gang_lookup(&dev->reada_zones,
609                                              (void **)&zone, index, 1);
610                 if (ret == 0)
611                         break;
612                 index = (zone->end >> PAGE_SHIFT) + 1;
613                 if (zone->locked) {
614                         if (zone->elems > top_locked_elems) {
615                                 top_locked_elems = zone->elems;
616                                 top_locked_zone = zone;
617                         }
618                 } else {
619                         if (zone->elems > top_elems) {
620                                 top_elems = zone->elems;
621                                 top_zone = zone;
622                         }
623                 }
624         }
625         if (top_zone)
626                 dev->reada_curr_zone = top_zone;
627         else if (top_locked_zone)
628                 dev->reada_curr_zone = top_locked_zone;
629         else
630                 return 0;
631 
632         dev->reada_next = dev->reada_curr_zone->start;
633         kref_get(&dev->reada_curr_zone->refcnt);
634         reada_peer_zones_set_lock(dev->reada_curr_zone, 1);
635 
636         return 1;
637 }
638 
639 static int reada_start_machine_dev(struct btrfs_device *dev)
640 {
641         struct btrfs_fs_info *fs_info = dev->fs_info;
642         struct reada_extent *re = NULL;
643         int mirror_num = 0;
644         struct extent_buffer *eb = NULL;
645         u64 logical;
646         int ret;
647         int i;
648 
649         spin_lock(&fs_info->reada_lock);
650         if (dev->reada_curr_zone == NULL) {
651                 ret = reada_pick_zone(dev);
652                 if (!ret) {
653                         spin_unlock(&fs_info->reada_lock);
654                         return 0;
655                 }
656         }
657         /*
658          * FIXME currently we issue the reads one extent at a time. If we have
659          * a contiguous block of extents, we could also coagulate them or use
660          * plugging to speed things up
661          */
662         ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
663                                      dev->reada_next >> PAGE_SHIFT, 1);
664         if (ret == 0 || re->logical > dev->reada_curr_zone->end) {
665                 ret = reada_pick_zone(dev);
666                 if (!ret) {
667                         spin_unlock(&fs_info->reada_lock);
668                         return 0;
669                 }
670                 re = NULL;
671                 ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
672                                         dev->reada_next >> PAGE_SHIFT, 1);
673         }
674         if (ret == 0) {
675                 spin_unlock(&fs_info->reada_lock);
676                 return 0;
677         }
678         dev->reada_next = re->logical + fs_info->nodesize;
679         re->refcnt++;
680 
681         spin_unlock(&fs_info->reada_lock);
682 
683         spin_lock(&re->lock);
684         if (re->scheduled || list_empty(&re->extctl)) {
685                 spin_unlock(&re->lock);
686                 reada_extent_put(fs_info, re);
687                 return 0;
688         }
689         re->scheduled = 1;
690         spin_unlock(&re->lock);
691 
692         /*
693          * find mirror num
694          */
695         for (i = 0; i < re->nzones; ++i) {
696                 if (re->zones[i]->device == dev) {
697                         mirror_num = i + 1;
698                         break;
699                 }
700         }
701         logical = re->logical;
702 
703         atomic_inc(&dev->reada_in_flight);
704         ret = reada_tree_block_flagged(fs_info, logical, mirror_num, &eb);
705         if (ret)
706                 __readahead_hook(fs_info, re, NULL, ret);
707         else if (eb)
708                 __readahead_hook(fs_info, re, eb, ret);
709 
710         if (eb)
711                 free_extent_buffer(eb);
712 
713         atomic_dec(&dev->reada_in_flight);
714         reada_extent_put(fs_info, re);
715 
716         return 1;
717 
718 }
719 
720 static void reada_start_machine_worker(struct btrfs_work *work)
721 {
722         struct reada_machine_work *rmw;
723         struct btrfs_fs_info *fs_info;
724         int old_ioprio;
725 
726         rmw = container_of(work, struct reada_machine_work, work);
727         fs_info = rmw->fs_info;
728 
729         kfree(rmw);
730 
731         old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
732                                        task_nice_ioprio(current));
733         set_task_ioprio(current, BTRFS_IOPRIO_READA);
734         __reada_start_machine(fs_info);
735         set_task_ioprio(current, old_ioprio);
736 
737         atomic_dec(&fs_info->reada_works_cnt);
738 }
739 
740 static void __reada_start_machine(struct btrfs_fs_info *fs_info)
741 {
742         struct btrfs_device *device;
743         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
744         u64 enqueued;
745         u64 total = 0;
746         int i;
747 
748         do {
749                 enqueued = 0;
750                 mutex_lock(&fs_devices->device_list_mutex);
751                 list_for_each_entry(device, &fs_devices->devices, dev_list) {
752                         if (atomic_read(&device->reada_in_flight) <
753                             MAX_IN_FLIGHT)
754                                 enqueued += reada_start_machine_dev(device);
755                 }
756                 mutex_unlock(&fs_devices->device_list_mutex);
757                 total += enqueued;
758         } while (enqueued && total < 10000);
759 
760         if (enqueued == 0)
761                 return;
762 
763         /*
764          * If everything is already in the cache, this is effectively single
765          * threaded. To a) not hold the caller for too long and b) to utilize
766          * more cores, we broke the loop above after 10000 iterations and now
767          * enqueue to workers to finish it. This will distribute the load to
768          * the cores.
769          */
770         for (i = 0; i < 2; ++i) {
771                 reada_start_machine(fs_info);
772                 if (atomic_read(&fs_info->reada_works_cnt) >
773                     BTRFS_MAX_MIRRORS * 2)
774                         break;
775         }
776 }
777 
778 static void reada_start_machine(struct btrfs_fs_info *fs_info)
779 {
780         struct reada_machine_work *rmw;
781 
782         rmw = kzalloc(sizeof(*rmw), GFP_KERNEL);
783         if (!rmw) {
784                 /* FIXME we cannot handle this properly right now */
785                 BUG();
786         }
787         btrfs_init_work(&rmw->work, btrfs_readahead_helper,
788                         reada_start_machine_worker, NULL, NULL);
789         rmw->fs_info = fs_info;
790 
791         btrfs_queue_work(fs_info->readahead_workers, &rmw->work);
792         atomic_inc(&fs_info->reada_works_cnt);
793 }
794 
795 #ifdef DEBUG
796 static void dump_devs(struct btrfs_fs_info *fs_info, int all)
797 {
798         struct btrfs_device *device;
799         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
800         unsigned long index;
801         int ret;
802         int i;
803         int j;
804         int cnt;
805 
806         spin_lock(&fs_info->reada_lock);
807         list_for_each_entry(device, &fs_devices->devices, dev_list) {
808                 btrfs_debug(fs_info, "dev %lld has %d in flight", device->devid,
809                         atomic_read(&device->reada_in_flight));
810                 index = 0;
811                 while (1) {
812                         struct reada_zone *zone;
813                         ret = radix_tree_gang_lookup(&device->reada_zones,
814                                                      (void **)&zone, index, 1);
815                         if (ret == 0)
816                                 break;
817                         pr_debug("  zone %llu-%llu elems %llu locked %d devs",
818                                     zone->start, zone->end, zone->elems,
819                                     zone->locked);
820                         for (j = 0; j < zone->ndevs; ++j) {
821                                 pr_cont(" %lld",
822                                         zone->devs[j]->devid);
823                         }
824                         if (device->reada_curr_zone == zone)
825                                 pr_cont(" curr off %llu",
826                                         device->reada_next - zone->start);
827                         pr_cont("\n");
828                         index = (zone->end >> PAGE_SHIFT) + 1;
829                 }
830                 cnt = 0;
831                 index = 0;
832                 while (all) {
833                         struct reada_extent *re = NULL;
834 
835                         ret = radix_tree_gang_lookup(&device->reada_extents,
836                                                      (void **)&re, index, 1);
837                         if (ret == 0)
838                                 break;
839                         pr_debug("  re: logical %llu size %u empty %d scheduled %d",
840                                 re->logical, fs_info->nodesize,
841                                 list_empty(&re->extctl), re->scheduled);
842 
843                         for (i = 0; i < re->nzones; ++i) {
844                                 pr_cont(" zone %llu-%llu devs",
845                                         re->zones[i]->start,
846                                         re->zones[i]->end);
847                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
848                                         pr_cont(" %lld",
849                                                 re->zones[i]->devs[j]->devid);
850                                 }
851                         }
852                         pr_cont("\n");
853                         index = (re->logical >> PAGE_SHIFT) + 1;
854                         if (++cnt > 15)
855                                 break;
856                 }
857         }
858 
859         index = 0;
860         cnt = 0;
861         while (all) {
862                 struct reada_extent *re = NULL;
863 
864                 ret = radix_tree_gang_lookup(&fs_info->reada_tree, (void **)&re,
865                                              index, 1);
866                 if (ret == 0)
867                         break;
868                 if (!re->scheduled) {
869                         index = (re->logical >> PAGE_SHIFT) + 1;
870                         continue;
871                 }
872                 pr_debug("re: logical %llu size %u list empty %d scheduled %d",
873                         re->logical, fs_info->nodesize,
874                         list_empty(&re->extctl), re->scheduled);
875                 for (i = 0; i < re->nzones; ++i) {
876                         pr_cont(" zone %llu-%llu devs",
877                                 re->zones[i]->start,
878                                 re->zones[i]->end);
879                         for (j = 0; j < re->zones[i]->ndevs; ++j) {
880                                 pr_cont(" %lld",
881                                        re->zones[i]->devs[j]->devid);
882                         }
883                 }
884                 pr_cont("\n");
885                 index = (re->logical >> PAGE_SHIFT) + 1;
886         }
887         spin_unlock(&fs_info->reada_lock);
888 }
889 #endif
890 
891 /*
892  * interface
893  */
894 struct reada_control *btrfs_reada_add(struct btrfs_root *root,
895                         struct btrfs_key *key_start, struct btrfs_key *key_end)
896 {
897         struct reada_control *rc;
898         u64 start;
899         u64 generation;
900         int ret;
901         struct extent_buffer *node;
902         static struct btrfs_key max_key = {
903                 .objectid = (u64)-1,
904                 .type = (u8)-1,
905                 .offset = (u64)-1
906         };
907 
908         rc = kzalloc(sizeof(*rc), GFP_KERNEL);
909         if (!rc)
910                 return ERR_PTR(-ENOMEM);
911 
912         rc->fs_info = root->fs_info;
913         rc->key_start = *key_start;
914         rc->key_end = *key_end;
915         atomic_set(&rc->elems, 0);
916         init_waitqueue_head(&rc->wait);
917         kref_init(&rc->refcnt);
918         kref_get(&rc->refcnt); /* one ref for having elements */
919 
920         node = btrfs_root_node(root);
921         start = node->start;
922         generation = btrfs_header_generation(node);
923         free_extent_buffer(node);
924 
925         ret = reada_add_block(rc, start, &max_key, generation);
926         if (ret) {
927                 kfree(rc);
928                 return ERR_PTR(ret);
929         }
930 
931         reada_start_machine(root->fs_info);
932 
933         return rc;
934 }
935 
936 #ifdef DEBUG
937 int btrfs_reada_wait(void *handle)
938 {
939         struct reada_control *rc = handle;
940         struct btrfs_fs_info *fs_info = rc->fs_info;
941 
942         while (atomic_read(&rc->elems)) {
943                 if (!atomic_read(&fs_info->reada_works_cnt))
944                         reada_start_machine(fs_info);
945                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
946                                    5 * HZ);
947                 dump_devs(fs_info, atomic_read(&rc->elems) < 10 ? 1 : 0);
948         }
949 
950         dump_devs(fs_info, atomic_read(&rc->elems) < 10 ? 1 : 0);
951 
952         kref_put(&rc->refcnt, reada_control_release);
953 
954         return 0;
955 }
956 #else
957 int btrfs_reada_wait(void *handle)
958 {
959         struct reada_control *rc = handle;
960         struct btrfs_fs_info *fs_info = rc->fs_info;
961 
962         while (atomic_read(&rc->elems)) {
963                 if (!atomic_read(&fs_info->reada_works_cnt))
964                         reada_start_machine(fs_info);
965                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
966                                    (HZ + 9) / 10);
967         }
968 
969         kref_put(&rc->refcnt, reada_control_release);
970 
971         return 0;
972 }
973 #endif
974 
975 void btrfs_reada_detach(void *handle)
976 {
977         struct reada_control *rc = handle;
978 
979         kref_put(&rc->refcnt, reada_control_release);
980 }
981 

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