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

Version: ~ [ linux-5.4-rc7 ] ~ [ linux-5.3.11 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.84 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.154 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.201 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.201 ] ~ [ 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-3.16.77 ] ~ [ 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 ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  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 
 31 #undef DEBUG
 32 
 33 /*
 34  * This is the implementation for the generic read ahead framework.
 35  *
 36  * To trigger a readahead, btrfs_reada_add must be called. It will start
 37  * a read ahead for the given range [start, end) on tree root. The returned
 38  * handle can either be used to wait on the readahead to finish
 39  * (btrfs_reada_wait), or to send it to the background (btrfs_reada_detach).
 40  *
 41  * The read ahead works as follows:
 42  * On btrfs_reada_add, the root of the tree is inserted into a radix_tree.
 43  * reada_start_machine will then search for extents to prefetch and trigger
 44  * some reads. When a read finishes for a node, all contained node/leaf
 45  * pointers that lie in the given range will also be enqueued. The reads will
 46  * be triggered in sequential order, thus giving a big win over a naive
 47  * enumeration. It will also make use of multi-device layouts. Each disk
 48  * will have its on read pointer and all disks will by utilized in parallel.
 49  * Also will no two disks read both sides of a mirror simultaneously, as this
 50  * would waste seeking capacity. Instead both disks will read different parts
 51  * of the filesystem.
 52  * Any number of readaheads can be started in parallel. The read order will be
 53  * determined globally, i.e. 2 parallel readaheads will normally finish faster
 54  * than the 2 started one after another.
 55  */
 56 
 57 #define MAX_IN_FLIGHT 6
 58 
 59 struct reada_extctl {
 60         struct list_head        list;
 61         struct reada_control    *rc;
 62         u64                     generation;
 63 };
 64 
 65 struct reada_extent {
 66         u64                     logical;
 67         struct btrfs_key        top;
 68         u32                     blocksize;
 69         int                     err;
 70         struct list_head        extctl;
 71         int                     refcnt;
 72         spinlock_t              lock;
 73         struct reada_zone       *zones[BTRFS_MAX_MIRRORS];
 74         int                     nzones;
 75         struct btrfs_device     *scheduled_for;
 76 };
 77 
 78 struct reada_zone {
 79         u64                     start;
 80         u64                     end;
 81         u64                     elems;
 82         struct list_head        list;
 83         spinlock_t              lock;
 84         int                     locked;
 85         struct btrfs_device     *device;
 86         struct btrfs_device     *devs[BTRFS_MAX_MIRRORS]; /* full list, incl
 87                                                            * self */
 88         int                     ndevs;
 89         struct kref             refcnt;
 90 };
 91 
 92 struct reada_machine_work {
 93         struct btrfs_work       work;
 94         struct btrfs_fs_info    *fs_info;
 95 };
 96 
 97 static void reada_extent_put(struct btrfs_fs_info *, struct reada_extent *);
 98 static void reada_control_release(struct kref *kref);
 99 static void reada_zone_release(struct kref *kref);
100 static void reada_start_machine(struct btrfs_fs_info *fs_info);
101 static void __reada_start_machine(struct btrfs_fs_info *fs_info);
102 
103 static int reada_add_block(struct reada_control *rc, u64 logical,
104                            struct btrfs_key *top, int level, u64 generation);
105 
106 /* recurses */
107 /* in case of err, eb might be NULL */
108 static int __readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
109                             u64 start, int err)
110 {
111         int level = 0;
112         int nritems;
113         int i;
114         u64 bytenr;
115         u64 generation;
116         struct reada_extent *re;
117         struct btrfs_fs_info *fs_info = root->fs_info;
118         struct list_head list;
119         unsigned long index = start >> PAGE_CACHE_SHIFT;
120         struct btrfs_device *for_dev;
121 
122         if (eb)
123                 level = btrfs_header_level(eb);
124 
125         /* find extent */
126         spin_lock(&fs_info->reada_lock);
127         re = radix_tree_lookup(&fs_info->reada_tree, index);
128         if (re)
129                 re->refcnt++;
130         spin_unlock(&fs_info->reada_lock);
131 
132         if (!re)
133                 return -1;
134 
135         spin_lock(&re->lock);
136         /*
137          * just take the full list from the extent. afterwards we
138          * don't need the lock anymore
139          */
140         list_replace_init(&re->extctl, &list);
141         for_dev = re->scheduled_for;
142         re->scheduled_for = NULL;
143         spin_unlock(&re->lock);
144 
145         if (err == 0) {
146                 nritems = level ? btrfs_header_nritems(eb) : 0;
147                 generation = btrfs_header_generation(eb);
148                 /*
149                  * FIXME: currently we just set nritems to 0 if this is a leaf,
150                  * effectively ignoring the content. In a next step we could
151                  * trigger more readahead depending from the content, e.g.
152                  * fetch the checksums for the extents in the leaf.
153                  */
154         } else {
155                 /*
156                  * this is the error case, the extent buffer has not been
157                  * read correctly. We won't access anything from it and
158                  * just cleanup our data structures. Effectively this will
159                  * cut the branch below this node from read ahead.
160                  */
161                 nritems = 0;
162                 generation = 0;
163         }
164 
165         for (i = 0; i < nritems; i++) {
166                 struct reada_extctl *rec;
167                 u64 n_gen;
168                 struct btrfs_key key;
169                 struct btrfs_key next_key;
170 
171                 btrfs_node_key_to_cpu(eb, &key, i);
172                 if (i + 1 < nritems)
173                         btrfs_node_key_to_cpu(eb, &next_key, i + 1);
174                 else
175                         next_key = re->top;
176                 bytenr = btrfs_node_blockptr(eb, i);
177                 n_gen = btrfs_node_ptr_generation(eb, i);
178 
179                 list_for_each_entry(rec, &list, list) {
180                         struct reada_control *rc = rec->rc;
181 
182                         /*
183                          * if the generation doesn't match, just ignore this
184                          * extctl. This will probably cut off a branch from
185                          * prefetch. Alternatively one could start a new (sub-)
186                          * prefetch for this branch, starting again from root.
187                          * FIXME: move the generation check out of this loop
188                          */
189 #ifdef DEBUG
190                         if (rec->generation != generation) {
191                                 printk(KERN_DEBUG "generation mismatch for "
192                                                 "(%llu,%d,%llu) %llu != %llu\n",
193                                        key.objectid, key.type, key.offset,
194                                        rec->generation, generation);
195                         }
196 #endif
197                         if (rec->generation == generation &&
198                             btrfs_comp_cpu_keys(&key, &rc->key_end) < 0 &&
199                             btrfs_comp_cpu_keys(&next_key, &rc->key_start) > 0)
200                                 reada_add_block(rc, bytenr, &next_key,
201                                                 level - 1, n_gen);
202                 }
203         }
204         /*
205          * free extctl records
206          */
207         while (!list_empty(&list)) {
208                 struct reada_control *rc;
209                 struct reada_extctl *rec;
210 
211                 rec = list_first_entry(&list, struct reada_extctl, list);
212                 list_del(&rec->list);
213                 rc = rec->rc;
214                 kfree(rec);
215 
216                 kref_get(&rc->refcnt);
217                 if (atomic_dec_and_test(&rc->elems)) {
218                         kref_put(&rc->refcnt, reada_control_release);
219                         wake_up(&rc->wait);
220                 }
221                 kref_put(&rc->refcnt, reada_control_release);
222 
223                 reada_extent_put(fs_info, re);  /* one ref for each entry */
224         }
225         reada_extent_put(fs_info, re);  /* our ref */
226         if (for_dev)
227                 atomic_dec(&for_dev->reada_in_flight);
228 
229         return 0;
230 }
231 
232 /*
233  * start is passed separately in case eb in NULL, which may be the case with
234  * failed I/O
235  */
236 int btree_readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
237                          u64 start, int err)
238 {
239         int ret;
240 
241         ret = __readahead_hook(root, eb, start, err);
242 
243         reada_start_machine(root->fs_info);
244 
245         return ret;
246 }
247 
248 static struct reada_zone *reada_find_zone(struct btrfs_fs_info *fs_info,
249                                           struct btrfs_device *dev, u64 logical,
250                                           struct btrfs_bio *bbio)
251 {
252         int ret;
253         struct reada_zone *zone;
254         struct btrfs_block_group_cache *cache = NULL;
255         u64 start;
256         u64 end;
257         int i;
258 
259         zone = NULL;
260         spin_lock(&fs_info->reada_lock);
261         ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
262                                      logical >> PAGE_CACHE_SHIFT, 1);
263         if (ret == 1)
264                 kref_get(&zone->refcnt);
265         spin_unlock(&fs_info->reada_lock);
266 
267         if (ret == 1) {
268                 if (logical >= zone->start && logical < zone->end)
269                         return zone;
270                 spin_lock(&fs_info->reada_lock);
271                 kref_put(&zone->refcnt, reada_zone_release);
272                 spin_unlock(&fs_info->reada_lock);
273         }
274 
275         cache = btrfs_lookup_block_group(fs_info, logical);
276         if (!cache)
277                 return NULL;
278 
279         start = cache->key.objectid;
280         end = start + cache->key.offset - 1;
281         btrfs_put_block_group(cache);
282 
283         zone = kzalloc(sizeof(*zone), GFP_NOFS);
284         if (!zone)
285                 return NULL;
286 
287         zone->start = start;
288         zone->end = end;
289         INIT_LIST_HEAD(&zone->list);
290         spin_lock_init(&zone->lock);
291         zone->locked = 0;
292         kref_init(&zone->refcnt);
293         zone->elems = 0;
294         zone->device = dev; /* our device always sits at index 0 */
295         for (i = 0; i < bbio->num_stripes; ++i) {
296                 /* bounds have already been checked */
297                 zone->devs[i] = bbio->stripes[i].dev;
298         }
299         zone->ndevs = bbio->num_stripes;
300 
301         spin_lock(&fs_info->reada_lock);
302         ret = radix_tree_insert(&dev->reada_zones,
303                                 (unsigned long)(zone->end >> PAGE_CACHE_SHIFT),
304                                 zone);
305 
306         if (ret == -EEXIST) {
307                 kfree(zone);
308                 ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
309                                              logical >> PAGE_CACHE_SHIFT, 1);
310                 if (ret == 1)
311                         kref_get(&zone->refcnt);
312         }
313         spin_unlock(&fs_info->reada_lock);
314 
315         return zone;
316 }
317 
318 static struct reada_extent *reada_find_extent(struct btrfs_root *root,
319                                               u64 logical,
320                                               struct btrfs_key *top, int level)
321 {
322         int ret;
323         struct reada_extent *re = NULL;
324         struct reada_extent *re_exist = NULL;
325         struct btrfs_fs_info *fs_info = root->fs_info;
326         struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
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 
336         spin_lock(&fs_info->reada_lock);
337         re = radix_tree_lookup(&fs_info->reada_tree, index);
338         if (re)
339                 re->refcnt++;
340         spin_unlock(&fs_info->reada_lock);
341 
342         if (re)
343                 return re;
344 
345         re = kzalloc(sizeof(*re), GFP_NOFS);
346         if (!re)
347                 return NULL;
348 
349         blocksize = btrfs_level_size(root, level);
350         re->logical = logical;
351         re->blocksize = blocksize;
352         re->top = *top;
353         INIT_LIST_HEAD(&re->extctl);
354         spin_lock_init(&re->lock);
355         re->refcnt = 1;
356 
357         /*
358          * map block
359          */
360         length = blocksize;
361         ret = btrfs_map_block(map_tree, REQ_WRITE, logical, &length, &bbio, 0);
362         if (ret || !bbio || length < blocksize)
363                 goto error;
364 
365         if (bbio->num_stripes > BTRFS_MAX_MIRRORS) {
366                 printk(KERN_ERR "btrfs readahead: more than %d copies not "
367                                 "supported", BTRFS_MAX_MIRRORS);
368                 goto error;
369         }
370 
371         for (nzones = 0; nzones < bbio->num_stripes; ++nzones) {
372                 struct reada_zone *zone;
373 
374                 dev = bbio->stripes[nzones].dev;
375                 zone = reada_find_zone(fs_info, dev, logical, bbio);
376                 if (!zone)
377                         break;
378 
379                 re->zones[nzones] = zone;
380                 spin_lock(&zone->lock);
381                 if (!zone->elems)
382                         kref_get(&zone->refcnt);
383                 ++zone->elems;
384                 spin_unlock(&zone->lock);
385                 spin_lock(&fs_info->reada_lock);
386                 kref_put(&zone->refcnt, reada_zone_release);
387                 spin_unlock(&fs_info->reada_lock);
388         }
389         re->nzones = nzones;
390         if (nzones == 0) {
391                 /* not a single zone found, error and out */
392                 goto error;
393         }
394 
395         /* insert extent in reada_tree + all per-device trees, all or nothing */
396         spin_lock(&fs_info->reada_lock);
397         ret = radix_tree_insert(&fs_info->reada_tree, index, re);
398         if (ret == -EEXIST) {
399                 re_exist = radix_tree_lookup(&fs_info->reada_tree, index);
400                 BUG_ON(!re_exist);
401                 re_exist->refcnt++;
402                 spin_unlock(&fs_info->reada_lock);
403                 goto error;
404         }
405         if (ret) {
406                 spin_unlock(&fs_info->reada_lock);
407                 goto error;
408         }
409         prev_dev = NULL;
410         for (i = 0; i < nzones; ++i) {
411                 dev = bbio->stripes[i].dev;
412                 if (dev == prev_dev) {
413                         /*
414                          * in case of DUP, just add the first zone. As both
415                          * are on the same device, there's nothing to gain
416                          * from adding both.
417                          * Also, it wouldn't work, as the tree is per device
418                          * and adding would fail with EEXIST
419                          */
420                         continue;
421                 }
422                 prev_dev = dev;
423                 ret = radix_tree_insert(&dev->reada_extents, index, re);
424                 if (ret) {
425                         while (--i >= 0) {
426                                 dev = bbio->stripes[i].dev;
427                                 BUG_ON(dev == NULL);
428                                 radix_tree_delete(&dev->reada_extents, index);
429                         }
430                         BUG_ON(fs_info == NULL);
431                         radix_tree_delete(&fs_info->reada_tree, index);
432                         spin_unlock(&fs_info->reada_lock);
433                         goto error;
434                 }
435         }
436         spin_unlock(&fs_info->reada_lock);
437 
438         kfree(bbio);
439         return re;
440 
441 error:
442         while (nzones) {
443                 struct reada_zone *zone;
444 
445                 --nzones;
446                 zone = re->zones[nzones];
447                 kref_get(&zone->refcnt);
448                 spin_lock(&zone->lock);
449                 --zone->elems;
450                 if (zone->elems == 0) {
451                         /*
452                          * no fs_info->reada_lock needed, as this can't be
453                          * the last ref
454                          */
455                         kref_put(&zone->refcnt, reada_zone_release);
456                 }
457                 spin_unlock(&zone->lock);
458 
459                 spin_lock(&fs_info->reada_lock);
460                 kref_put(&zone->refcnt, reada_zone_release);
461                 spin_unlock(&fs_info->reada_lock);
462         }
463         kfree(bbio);
464         kfree(re);
465         return re_exist;
466 }
467 
468 static void reada_extent_put(struct btrfs_fs_info *fs_info,
469                              struct reada_extent *re)
470 {
471         int i;
472         unsigned long index = re->logical >> PAGE_CACHE_SHIFT;
473 
474         spin_lock(&fs_info->reada_lock);
475         if (--re->refcnt) {
476                 spin_unlock(&fs_info->reada_lock);
477                 return;
478         }
479 
480         radix_tree_delete(&fs_info->reada_tree, index);
481         for (i = 0; i < re->nzones; ++i) {
482                 struct reada_zone *zone = re->zones[i];
483 
484                 radix_tree_delete(&zone->device->reada_extents, index);
485         }
486 
487         spin_unlock(&fs_info->reada_lock);
488 
489         for (i = 0; i < re->nzones; ++i) {
490                 struct reada_zone *zone = re->zones[i];
491 
492                 kref_get(&zone->refcnt);
493                 spin_lock(&zone->lock);
494                 --zone->elems;
495                 if (zone->elems == 0) {
496                         /* no fs_info->reada_lock needed, as this can't be
497                          * the last ref */
498                         kref_put(&zone->refcnt, reada_zone_release);
499                 }
500                 spin_unlock(&zone->lock);
501 
502                 spin_lock(&fs_info->reada_lock);
503                 kref_put(&zone->refcnt, reada_zone_release);
504                 spin_unlock(&fs_info->reada_lock);
505         }
506         if (re->scheduled_for)
507                 atomic_dec(&re->scheduled_for->reada_in_flight);
508 
509         kfree(re);
510 }
511 
512 static void reada_zone_release(struct kref *kref)
513 {
514         struct reada_zone *zone = container_of(kref, struct reada_zone, refcnt);
515 
516         radix_tree_delete(&zone->device->reada_zones,
517                           zone->end >> PAGE_CACHE_SHIFT);
518 
519         kfree(zone);
520 }
521 
522 static void reada_control_release(struct kref *kref)
523 {
524         struct reada_control *rc = container_of(kref, struct reada_control,
525                                                 refcnt);
526 
527         kfree(rc);
528 }
529 
530 static int reada_add_block(struct reada_control *rc, u64 logical,
531                            struct btrfs_key *top, int level, u64 generation)
532 {
533         struct btrfs_root *root = rc->root;
534         struct reada_extent *re;
535         struct reada_extctl *rec;
536 
537         re = reada_find_extent(root, logical, top, level); /* takes one ref */
538         if (!re)
539                 return -1;
540 
541         rec = kzalloc(sizeof(*rec), GFP_NOFS);
542         if (!rec) {
543                 reada_extent_put(root->fs_info, re);
544                 return -1;
545         }
546 
547         rec->rc = rc;
548         rec->generation = generation;
549         atomic_inc(&rc->elems);
550 
551         spin_lock(&re->lock);
552         list_add_tail(&rec->list, &re->extctl);
553         spin_unlock(&re->lock);
554 
555         /* leave the ref on the extent */
556 
557         return 0;
558 }
559 
560 /*
561  * called with fs_info->reada_lock held
562  */
563 static void reada_peer_zones_set_lock(struct reada_zone *zone, int lock)
564 {
565         int i;
566         unsigned long index = zone->end >> PAGE_CACHE_SHIFT;
567 
568         for (i = 0; i < zone->ndevs; ++i) {
569                 struct reada_zone *peer;
570                 peer = radix_tree_lookup(&zone->devs[i]->reada_zones, index);
571                 if (peer && peer->device != zone->device)
572                         peer->locked = lock;
573         }
574 }
575 
576 /*
577  * called with fs_info->reada_lock held
578  */
579 static int reada_pick_zone(struct btrfs_device *dev)
580 {
581         struct reada_zone *top_zone = NULL;
582         struct reada_zone *top_locked_zone = NULL;
583         u64 top_elems = 0;
584         u64 top_locked_elems = 0;
585         unsigned long index = 0;
586         int ret;
587 
588         if (dev->reada_curr_zone) {
589                 reada_peer_zones_set_lock(dev->reada_curr_zone, 0);
590                 kref_put(&dev->reada_curr_zone->refcnt, reada_zone_release);
591                 dev->reada_curr_zone = NULL;
592         }
593         /* pick the zone with the most elements */
594         while (1) {
595                 struct reada_zone *zone;
596 
597                 ret = radix_tree_gang_lookup(&dev->reada_zones,
598                                              (void **)&zone, index, 1);
599                 if (ret == 0)
600                         break;
601                 index = (zone->end >> PAGE_CACHE_SHIFT) + 1;
602                 if (zone->locked) {
603                         if (zone->elems > top_locked_elems) {
604                                 top_locked_elems = zone->elems;
605                                 top_locked_zone = zone;
606                         }
607                 } else {
608                         if (zone->elems > top_elems) {
609                                 top_elems = zone->elems;
610                                 top_zone = zone;
611                         }
612                 }
613         }
614         if (top_zone)
615                 dev->reada_curr_zone = top_zone;
616         else if (top_locked_zone)
617                 dev->reada_curr_zone = top_locked_zone;
618         else
619                 return 0;
620 
621         dev->reada_next = dev->reada_curr_zone->start;
622         kref_get(&dev->reada_curr_zone->refcnt);
623         reada_peer_zones_set_lock(dev->reada_curr_zone, 1);
624 
625         return 1;
626 }
627 
628 static int reada_start_machine_dev(struct btrfs_fs_info *fs_info,
629                                    struct btrfs_device *dev)
630 {
631         struct reada_extent *re = NULL;
632         int mirror_num = 0;
633         struct extent_buffer *eb = NULL;
634         u64 logical;
635         u32 blocksize;
636         int ret;
637         int i;
638         int need_kick = 0;
639 
640         spin_lock(&fs_info->reada_lock);
641         if (dev->reada_curr_zone == NULL) {
642                 ret = reada_pick_zone(dev);
643                 if (!ret) {
644                         spin_unlock(&fs_info->reada_lock);
645                         return 0;
646                 }
647         }
648         /*
649          * FIXME currently we issue the reads one extent at a time. If we have
650          * a contiguous block of extents, we could also coagulate them or use
651          * plugging to speed things up
652          */
653         ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
654                                      dev->reada_next >> PAGE_CACHE_SHIFT, 1);
655         if (ret == 0 || re->logical >= dev->reada_curr_zone->end) {
656                 ret = reada_pick_zone(dev);
657                 if (!ret) {
658                         spin_unlock(&fs_info->reada_lock);
659                         return 0;
660                 }
661                 re = NULL;
662                 ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
663                                         dev->reada_next >> PAGE_CACHE_SHIFT, 1);
664         }
665         if (ret == 0) {
666                 spin_unlock(&fs_info->reada_lock);
667                 return 0;
668         }
669         dev->reada_next = re->logical + re->blocksize;
670         re->refcnt++;
671 
672         spin_unlock(&fs_info->reada_lock);
673 
674         /*
675          * find mirror num
676          */
677         for (i = 0; i < re->nzones; ++i) {
678                 if (re->zones[i]->device == dev) {
679                         mirror_num = i + 1;
680                         break;
681                 }
682         }
683         logical = re->logical;
684         blocksize = re->blocksize;
685 
686         spin_lock(&re->lock);
687         if (re->scheduled_for == NULL) {
688                 re->scheduled_for = dev;
689                 need_kick = 1;
690         }
691         spin_unlock(&re->lock);
692 
693         reada_extent_put(fs_info, re);
694 
695         if (!need_kick)
696                 return 0;
697 
698         atomic_inc(&dev->reada_in_flight);
699         ret = reada_tree_block_flagged(fs_info->extent_root, logical, blocksize,
700                          mirror_num, &eb);
701         if (ret)
702                 __readahead_hook(fs_info->extent_root, NULL, logical, ret);
703         else if (eb)
704                 __readahead_hook(fs_info->extent_root, eb, eb->start, ret);
705 
706         if (eb)
707                 free_extent_buffer(eb);
708 
709         return 1;
710 
711 }
712 
713 static void reada_start_machine_worker(struct btrfs_work *work)
714 {
715         struct reada_machine_work *rmw;
716         struct btrfs_fs_info *fs_info;
717         int old_ioprio;
718 
719         rmw = container_of(work, struct reada_machine_work, work);
720         fs_info = rmw->fs_info;
721 
722         kfree(rmw);
723 
724         old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
725                                        task_nice_ioprio(current));
726         set_task_ioprio(current, BTRFS_IOPRIO_READA);
727         __reada_start_machine(fs_info);
728         set_task_ioprio(current, old_ioprio);
729 }
730 
731 static void __reada_start_machine(struct btrfs_fs_info *fs_info)
732 {
733         struct btrfs_device *device;
734         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
735         u64 enqueued;
736         u64 total = 0;
737         int i;
738 
739         do {
740                 enqueued = 0;
741                 list_for_each_entry(device, &fs_devices->devices, dev_list) {
742                         if (atomic_read(&device->reada_in_flight) <
743                             MAX_IN_FLIGHT)
744                                 enqueued += reada_start_machine_dev(fs_info,
745                                                                     device);
746                 }
747                 total += enqueued;
748         } while (enqueued && total < 10000);
749 
750         if (enqueued == 0)
751                 return;
752 
753         /*
754          * If everything is already in the cache, this is effectively single
755          * threaded. To a) not hold the caller for too long and b) to utilize
756          * more cores, we broke the loop above after 10000 iterations and now
757          * enqueue to workers to finish it. This will distribute the load to
758          * the cores.
759          */
760         for (i = 0; i < 2; ++i)
761                 reada_start_machine(fs_info);
762 }
763 
764 static void reada_start_machine(struct btrfs_fs_info *fs_info)
765 {
766         struct reada_machine_work *rmw;
767 
768         rmw = kzalloc(sizeof(*rmw), GFP_NOFS);
769         if (!rmw) {
770                 /* FIXME we cannot handle this properly right now */
771                 BUG();
772         }
773         rmw->work.func = reada_start_machine_worker;
774         rmw->fs_info = fs_info;
775 
776         btrfs_queue_worker(&fs_info->readahead_workers, &rmw->work);
777 }
778 
779 #ifdef DEBUG
780 static void dump_devs(struct btrfs_fs_info *fs_info, int all)
781 {
782         struct btrfs_device *device;
783         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
784         unsigned long index;
785         int ret;
786         int i;
787         int j;
788         int cnt;
789 
790         spin_lock(&fs_info->reada_lock);
791         list_for_each_entry(device, &fs_devices->devices, dev_list) {
792                 printk(KERN_DEBUG "dev %lld has %d in flight\n", device->devid,
793                         atomic_read(&device->reada_in_flight));
794                 index = 0;
795                 while (1) {
796                         struct reada_zone *zone;
797                         ret = radix_tree_gang_lookup(&device->reada_zones,
798                                                      (void **)&zone, index, 1);
799                         if (ret == 0)
800                                 break;
801                         printk(KERN_DEBUG "  zone %llu-%llu elems %llu locked "
802                                 "%d devs", zone->start, zone->end, zone->elems,
803                                 zone->locked);
804                         for (j = 0; j < zone->ndevs; ++j) {
805                                 printk(KERN_CONT " %lld",
806                                         zone->devs[j]->devid);
807                         }
808                         if (device->reada_curr_zone == zone)
809                                 printk(KERN_CONT " curr off %llu",
810                                         device->reada_next - zone->start);
811                         printk(KERN_CONT "\n");
812                         index = (zone->end >> PAGE_CACHE_SHIFT) + 1;
813                 }
814                 cnt = 0;
815                 index = 0;
816                 while (all) {
817                         struct reada_extent *re = NULL;
818 
819                         ret = radix_tree_gang_lookup(&device->reada_extents,
820                                                      (void **)&re, index, 1);
821                         if (ret == 0)
822                                 break;
823                         printk(KERN_DEBUG
824                                 "  re: logical %llu size %u empty %d for %lld",
825                                 re->logical, re->blocksize,
826                                 list_empty(&re->extctl), re->scheduled_for ?
827                                 re->scheduled_for->devid : -1);
828 
829                         for (i = 0; i < re->nzones; ++i) {
830                                 printk(KERN_CONT " zone %llu-%llu devs",
831                                         re->zones[i]->start,
832                                         re->zones[i]->end);
833                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
834                                         printk(KERN_CONT " %lld",
835                                                 re->zones[i]->devs[j]->devid);
836                                 }
837                         }
838                         printk(KERN_CONT "\n");
839                         index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
840                         if (++cnt > 15)
841                                 break;
842                 }
843         }
844 
845         index = 0;
846         cnt = 0;
847         while (all) {
848                 struct reada_extent *re = NULL;
849 
850                 ret = radix_tree_gang_lookup(&fs_info->reada_tree, (void **)&re,
851                                              index, 1);
852                 if (ret == 0)
853                         break;
854                 if (!re->scheduled_for) {
855                         index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
856                         continue;
857                 }
858                 printk(KERN_DEBUG
859                         "re: logical %llu size %u list empty %d for %lld",
860                         re->logical, re->blocksize, list_empty(&re->extctl),
861                         re->scheduled_for ? re->scheduled_for->devid : -1);
862                 for (i = 0; i < re->nzones; ++i) {
863                         printk(KERN_CONT " zone %llu-%llu devs",
864                                 re->zones[i]->start,
865                                 re->zones[i]->end);
866                         for (i = 0; i < re->nzones; ++i) {
867                                 printk(KERN_CONT " zone %llu-%llu devs",
868                                         re->zones[i]->start,
869                                         re->zones[i]->end);
870                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
871                                         printk(KERN_CONT " %lld",
872                                                 re->zones[i]->devs[j]->devid);
873                                 }
874                         }
875                 }
876                 printk(KERN_CONT "\n");
877                 index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
878         }
879         spin_unlock(&fs_info->reada_lock);
880 }
881 #endif
882 
883 /*
884  * interface
885  */
886 struct reada_control *btrfs_reada_add(struct btrfs_root *root,
887                         struct btrfs_key *key_start, struct btrfs_key *key_end)
888 {
889         struct reada_control *rc;
890         u64 start;
891         u64 generation;
892         int level;
893         struct extent_buffer *node;
894         static struct btrfs_key max_key = {
895                 .objectid = (u64)-1,
896                 .type = (u8)-1,
897                 .offset = (u64)-1
898         };
899 
900         rc = kzalloc(sizeof(*rc), GFP_NOFS);
901         if (!rc)
902                 return ERR_PTR(-ENOMEM);
903 
904         rc->root = root;
905         rc->key_start = *key_start;
906         rc->key_end = *key_end;
907         atomic_set(&rc->elems, 0);
908         init_waitqueue_head(&rc->wait);
909         kref_init(&rc->refcnt);
910         kref_get(&rc->refcnt); /* one ref for having elements */
911 
912         node = btrfs_root_node(root);
913         start = node->start;
914         level = btrfs_header_level(node);
915         generation = btrfs_header_generation(node);
916         free_extent_buffer(node);
917 
918         reada_add_block(rc, start, &max_key, level, generation);
919 
920         reada_start_machine(root->fs_info);
921 
922         return rc;
923 }
924 
925 #ifdef DEBUG
926 int btrfs_reada_wait(void *handle)
927 {
928         struct reada_control *rc = handle;
929 
930         while (atomic_read(&rc->elems)) {
931                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
932                                    5 * HZ);
933                 dump_devs(rc->root->fs_info, rc->elems < 10 ? 1 : 0);
934         }
935 
936         dump_devs(rc->root->fs_info, rc->elems < 10 ? 1 : 0);
937 
938         kref_put(&rc->refcnt, reada_control_release);
939 
940         return 0;
941 }
942 #else
943 int btrfs_reada_wait(void *handle)
944 {
945         struct reada_control *rc = handle;
946 
947         while (atomic_read(&rc->elems)) {
948                 wait_event(rc->wait, atomic_read(&rc->elems) == 0);
949         }
950 
951         kref_put(&rc->refcnt, reada_control_release);
952 
953         return 0;
954 }
955 #endif
956 
957 void btrfs_reada_detach(void *handle)
958 {
959         struct reada_control *rc = handle;
960 
961         kref_put(&rc->refcnt, reada_control_release);
962 }
963 

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