Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/mm/backing-dev.c

  1 
  2 #include <linux/wait.h>
  3 #include <linux/backing-dev.h>
  4 #include <linux/kthread.h>
  5 #include <linux/freezer.h>
  6 #include <linux/fs.h>
  7 #include <linux/pagemap.h>
  8 #include <linux/mm.h>
  9 #include <linux/sched.h>
 10 #include <linux/module.h>
 11 #include <linux/writeback.h>
 12 #include <linux/device.h>
 13 #include <trace/events/writeback.h>
 14 
 15 static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
 16 
 17 struct backing_dev_info noop_backing_dev_info = {
 18         .name           = "noop",
 19         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
 20 };
 21 EXPORT_SYMBOL_GPL(noop_backing_dev_info);
 22 
 23 static struct class *bdi_class;
 24 
 25 /*
 26  * bdi_lock protects updates to bdi_list. bdi_list has RCU reader side
 27  * locking.
 28  */
 29 DEFINE_SPINLOCK(bdi_lock);
 30 LIST_HEAD(bdi_list);
 31 
 32 /* bdi_wq serves all asynchronous writeback tasks */
 33 struct workqueue_struct *bdi_wq;
 34 
 35 #ifdef CONFIG_DEBUG_FS
 36 #include <linux/debugfs.h>
 37 #include <linux/seq_file.h>
 38 
 39 static struct dentry *bdi_debug_root;
 40 
 41 static void bdi_debug_init(void)
 42 {
 43         bdi_debug_root = debugfs_create_dir("bdi", NULL);
 44 }
 45 
 46 static int bdi_debug_stats_show(struct seq_file *m, void *v)
 47 {
 48         struct backing_dev_info *bdi = m->private;
 49         struct bdi_writeback *wb = &bdi->wb;
 50         unsigned long background_thresh;
 51         unsigned long dirty_thresh;
 52         unsigned long wb_thresh;
 53         unsigned long nr_dirty, nr_io, nr_more_io, nr_dirty_time;
 54         struct inode *inode;
 55 
 56         nr_dirty = nr_io = nr_more_io = nr_dirty_time = 0;
 57         spin_lock(&wb->list_lock);
 58         list_for_each_entry(inode, &wb->b_dirty, i_io_list)
 59                 nr_dirty++;
 60         list_for_each_entry(inode, &wb->b_io, i_io_list)
 61                 nr_io++;
 62         list_for_each_entry(inode, &wb->b_more_io, i_io_list)
 63                 nr_more_io++;
 64         list_for_each_entry(inode, &wb->b_dirty_time, i_io_list)
 65                 if (inode->i_state & I_DIRTY_TIME)
 66                         nr_dirty_time++;
 67         spin_unlock(&wb->list_lock);
 68 
 69         global_dirty_limits(&background_thresh, &dirty_thresh);
 70         wb_thresh = wb_calc_thresh(wb, dirty_thresh);
 71 
 72 #define K(x) ((x) << (PAGE_SHIFT - 10))
 73         seq_printf(m,
 74                    "BdiWriteback:       %10lu kB\n"
 75                    "BdiReclaimable:     %10lu kB\n"
 76                    "BdiDirtyThresh:     %10lu kB\n"
 77                    "DirtyThresh:        %10lu kB\n"
 78                    "BackgroundThresh:   %10lu kB\n"
 79                    "BdiDirtied:         %10lu kB\n"
 80                    "BdiWritten:         %10lu kB\n"
 81                    "BdiWriteBandwidth:  %10lu kBps\n"
 82                    "b_dirty:            %10lu\n"
 83                    "b_io:               %10lu\n"
 84                    "b_more_io:          %10lu\n"
 85                    "b_dirty_time:       %10lu\n"
 86                    "bdi_list:           %10u\n"
 87                    "state:              %10lx\n",
 88                    (unsigned long) K(wb_stat(wb, WB_WRITEBACK)),
 89                    (unsigned long) K(wb_stat(wb, WB_RECLAIMABLE)),
 90                    K(wb_thresh),
 91                    K(dirty_thresh),
 92                    K(background_thresh),
 93                    (unsigned long) K(wb_stat(wb, WB_DIRTIED)),
 94                    (unsigned long) K(wb_stat(wb, WB_WRITTEN)),
 95                    (unsigned long) K(wb->write_bandwidth),
 96                    nr_dirty,
 97                    nr_io,
 98                    nr_more_io,
 99                    nr_dirty_time,
100                    !list_empty(&bdi->bdi_list), bdi->wb.state);
101 #undef K
102 
103         return 0;
104 }
105 
106 static int bdi_debug_stats_open(struct inode *inode, struct file *file)
107 {
108         return single_open(file, bdi_debug_stats_show, inode->i_private);
109 }
110 
111 static const struct file_operations bdi_debug_stats_fops = {
112         .open           = bdi_debug_stats_open,
113         .read           = seq_read,
114         .llseek         = seq_lseek,
115         .release        = single_release,
116 };
117 
118 static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
119 {
120         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
121         bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
122                                                bdi, &bdi_debug_stats_fops);
123 }
124 
125 static void bdi_debug_unregister(struct backing_dev_info *bdi)
126 {
127         debugfs_remove(bdi->debug_stats);
128         debugfs_remove(bdi->debug_dir);
129 }
130 #else
131 static inline void bdi_debug_init(void)
132 {
133 }
134 static inline void bdi_debug_register(struct backing_dev_info *bdi,
135                                       const char *name)
136 {
137 }
138 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
139 {
140 }
141 #endif
142 
143 static ssize_t read_ahead_kb_store(struct device *dev,
144                                   struct device_attribute *attr,
145                                   const char *buf, size_t count)
146 {
147         struct backing_dev_info *bdi = dev_get_drvdata(dev);
148         unsigned long read_ahead_kb;
149         ssize_t ret;
150 
151         ret = kstrtoul(buf, 10, &read_ahead_kb);
152         if (ret < 0)
153                 return ret;
154 
155         bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
156 
157         return count;
158 }
159 
160 #define K(pages) ((pages) << (PAGE_SHIFT - 10))
161 
162 #define BDI_SHOW(name, expr)                                            \
163 static ssize_t name##_show(struct device *dev,                          \
164                            struct device_attribute *attr, char *page)   \
165 {                                                                       \
166         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
167                                                                         \
168         return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
169 }                                                                       \
170 static DEVICE_ATTR_RW(name);
171 
172 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
173 
174 static ssize_t min_ratio_store(struct device *dev,
175                 struct device_attribute *attr, const char *buf, size_t count)
176 {
177         struct backing_dev_info *bdi = dev_get_drvdata(dev);
178         unsigned int ratio;
179         ssize_t ret;
180 
181         ret = kstrtouint(buf, 10, &ratio);
182         if (ret < 0)
183                 return ret;
184 
185         ret = bdi_set_min_ratio(bdi, ratio);
186         if (!ret)
187                 ret = count;
188 
189         return ret;
190 }
191 BDI_SHOW(min_ratio, bdi->min_ratio)
192 
193 static ssize_t max_ratio_store(struct device *dev,
194                 struct device_attribute *attr, const char *buf, size_t count)
195 {
196         struct backing_dev_info *bdi = dev_get_drvdata(dev);
197         unsigned int ratio;
198         ssize_t ret;
199 
200         ret = kstrtouint(buf, 10, &ratio);
201         if (ret < 0)
202                 return ret;
203 
204         ret = bdi_set_max_ratio(bdi, ratio);
205         if (!ret)
206                 ret = count;
207 
208         return ret;
209 }
210 BDI_SHOW(max_ratio, bdi->max_ratio)
211 
212 static ssize_t stable_pages_required_show(struct device *dev,
213                                           struct device_attribute *attr,
214                                           char *page)
215 {
216         struct backing_dev_info *bdi = dev_get_drvdata(dev);
217 
218         return snprintf(page, PAGE_SIZE-1, "%d\n",
219                         bdi_cap_stable_pages_required(bdi) ? 1 : 0);
220 }
221 static DEVICE_ATTR_RO(stable_pages_required);
222 
223 static struct attribute *bdi_dev_attrs[] = {
224         &dev_attr_read_ahead_kb.attr,
225         &dev_attr_min_ratio.attr,
226         &dev_attr_max_ratio.attr,
227         &dev_attr_stable_pages_required.attr,
228         NULL,
229 };
230 ATTRIBUTE_GROUPS(bdi_dev);
231 
232 static __init int bdi_class_init(void)
233 {
234         bdi_class = class_create(THIS_MODULE, "bdi");
235         if (IS_ERR(bdi_class))
236                 return PTR_ERR(bdi_class);
237 
238         bdi_class->dev_groups = bdi_dev_groups;
239         bdi_debug_init();
240         return 0;
241 }
242 postcore_initcall(bdi_class_init);
243 
244 static int __init default_bdi_init(void)
245 {
246         int err;
247 
248         bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE |
249                                               WQ_UNBOUND | WQ_SYSFS, 0);
250         if (!bdi_wq)
251                 return -ENOMEM;
252 
253         err = bdi_init(&noop_backing_dev_info);
254 
255         return err;
256 }
257 subsys_initcall(default_bdi_init);
258 
259 /*
260  * This function is used when the first inode for this wb is marked dirty. It
261  * wakes-up the corresponding bdi thread which should then take care of the
262  * periodic background write-out of dirty inodes. Since the write-out would
263  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
264  * set up a timer which wakes the bdi thread up later.
265  *
266  * Note, we wouldn't bother setting up the timer, but this function is on the
267  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
268  * by delaying the wake-up.
269  *
270  * We have to be careful not to postpone flush work if it is scheduled for
271  * earlier. Thus we use queue_delayed_work().
272  */
273 void wb_wakeup_delayed(struct bdi_writeback *wb)
274 {
275         unsigned long timeout;
276 
277         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
278         spin_lock_bh(&wb->work_lock);
279         if (test_bit(WB_registered, &wb->state))
280                 queue_delayed_work(bdi_wq, &wb->dwork, timeout);
281         spin_unlock_bh(&wb->work_lock);
282 }
283 
284 /*
285  * Initial write bandwidth: 100 MB/s
286  */
287 #define INIT_BW         (100 << (20 - PAGE_SHIFT))
288 
289 static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
290                    int blkcg_id, gfp_t gfp)
291 {
292         int i, err;
293 
294         memset(wb, 0, sizeof(*wb));
295 
296         wb->bdi = bdi;
297         wb->last_old_flush = jiffies;
298         INIT_LIST_HEAD(&wb->b_dirty);
299         INIT_LIST_HEAD(&wb->b_io);
300         INIT_LIST_HEAD(&wb->b_more_io);
301         INIT_LIST_HEAD(&wb->b_dirty_time);
302         spin_lock_init(&wb->list_lock);
303 
304         wb->bw_time_stamp = jiffies;
305         wb->balanced_dirty_ratelimit = INIT_BW;
306         wb->dirty_ratelimit = INIT_BW;
307         wb->write_bandwidth = INIT_BW;
308         wb->avg_write_bandwidth = INIT_BW;
309 
310         spin_lock_init(&wb->work_lock);
311         INIT_LIST_HEAD(&wb->work_list);
312         INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
313         wb->dirty_sleep = jiffies;
314 
315         wb->congested = wb_congested_get_create(bdi, blkcg_id, gfp);
316         if (!wb->congested)
317                 return -ENOMEM;
318 
319         err = fprop_local_init_percpu(&wb->completions, gfp);
320         if (err)
321                 goto out_put_cong;
322 
323         for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
324                 err = percpu_counter_init(&wb->stat[i], 0, gfp);
325                 if (err)
326                         goto out_destroy_stat;
327         }
328 
329         return 0;
330 
331 out_destroy_stat:
332         while (i--)
333                 percpu_counter_destroy(&wb->stat[i]);
334         fprop_local_destroy_percpu(&wb->completions);
335 out_put_cong:
336         wb_congested_put(wb->congested);
337         return err;
338 }
339 
340 /*
341  * Remove bdi from the global list and shutdown any threads we have running
342  */
343 static void wb_shutdown(struct bdi_writeback *wb)
344 {
345         /* Make sure nobody queues further work */
346         spin_lock_bh(&wb->work_lock);
347         if (!test_and_clear_bit(WB_registered, &wb->state)) {
348                 spin_unlock_bh(&wb->work_lock);
349                 return;
350         }
351         spin_unlock_bh(&wb->work_lock);
352 
353         /*
354          * Drain work list and shutdown the delayed_work.  !WB_registered
355          * tells wb_workfn() that @wb is dying and its work_list needs to
356          * be drained no matter what.
357          */
358         mod_delayed_work(bdi_wq, &wb->dwork, 0);
359         flush_delayed_work(&wb->dwork);
360         WARN_ON(!list_empty(&wb->work_list));
361 }
362 
363 static void wb_exit(struct bdi_writeback *wb)
364 {
365         int i;
366 
367         WARN_ON(delayed_work_pending(&wb->dwork));
368 
369         for (i = 0; i < NR_WB_STAT_ITEMS; i++)
370                 percpu_counter_destroy(&wb->stat[i]);
371 
372         fprop_local_destroy_percpu(&wb->completions);
373         wb_congested_put(wb->congested);
374 }
375 
376 #ifdef CONFIG_CGROUP_WRITEBACK
377 
378 #include <linux/memcontrol.h>
379 
380 /*
381  * cgwb_lock protects bdi->cgwb_tree, bdi->cgwb_congested_tree,
382  * blkcg->cgwb_list, and memcg->cgwb_list.  bdi->cgwb_tree is also RCU
383  * protected.  cgwb_release_wait is used to wait for the completion of cgwb
384  * releases from bdi destruction path.
385  */
386 static DEFINE_SPINLOCK(cgwb_lock);
387 static DECLARE_WAIT_QUEUE_HEAD(cgwb_release_wait);
388 
389 /**
390  * wb_congested_get_create - get or create a wb_congested
391  * @bdi: associated bdi
392  * @blkcg_id: ID of the associated blkcg
393  * @gfp: allocation mask
394  *
395  * Look up the wb_congested for @blkcg_id on @bdi.  If missing, create one.
396  * The returned wb_congested has its reference count incremented.  Returns
397  * NULL on failure.
398  */
399 struct bdi_writeback_congested *
400 wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
401 {
402         struct bdi_writeback_congested *new_congested = NULL, *congested;
403         struct rb_node **node, *parent;
404         unsigned long flags;
405 retry:
406         spin_lock_irqsave(&cgwb_lock, flags);
407 
408         node = &bdi->cgwb_congested_tree.rb_node;
409         parent = NULL;
410 
411         while (*node != NULL) {
412                 parent = *node;
413                 congested = container_of(parent, struct bdi_writeback_congested,
414                                          rb_node);
415                 if (congested->blkcg_id < blkcg_id)
416                         node = &parent->rb_left;
417                 else if (congested->blkcg_id > blkcg_id)
418                         node = &parent->rb_right;
419                 else
420                         goto found;
421         }
422 
423         if (new_congested) {
424                 /* !found and storage for new one already allocated, insert */
425                 congested = new_congested;
426                 new_congested = NULL;
427                 rb_link_node(&congested->rb_node, parent, node);
428                 rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
429                 goto found;
430         }
431 
432         spin_unlock_irqrestore(&cgwb_lock, flags);
433 
434         /* allocate storage for new one and retry */
435         new_congested = kzalloc(sizeof(*new_congested), gfp);
436         if (!new_congested)
437                 return NULL;
438 
439         atomic_set(&new_congested->refcnt, 0);
440         new_congested->bdi = bdi;
441         new_congested->blkcg_id = blkcg_id;
442         goto retry;
443 
444 found:
445         atomic_inc(&congested->refcnt);
446         spin_unlock_irqrestore(&cgwb_lock, flags);
447         kfree(new_congested);
448         return congested;
449 }
450 
451 /**
452  * wb_congested_put - put a wb_congested
453  * @congested: wb_congested to put
454  *
455  * Put @congested and destroy it if the refcnt reaches zero.
456  */
457 void wb_congested_put(struct bdi_writeback_congested *congested)
458 {
459         unsigned long flags;
460 
461         local_irq_save(flags);
462         if (!atomic_dec_and_lock(&congested->refcnt, &cgwb_lock)) {
463                 local_irq_restore(flags);
464                 return;
465         }
466 
467         /* bdi might already have been destroyed leaving @congested unlinked */
468         if (congested->bdi) {
469                 rb_erase(&congested->rb_node,
470                          &congested->bdi->cgwb_congested_tree);
471                 congested->bdi = NULL;
472         }
473 
474         spin_unlock_irqrestore(&cgwb_lock, flags);
475         kfree(congested);
476 }
477 
478 static void cgwb_release_workfn(struct work_struct *work)
479 {
480         struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
481                                                 release_work);
482         struct backing_dev_info *bdi = wb->bdi;
483 
484         spin_lock_irq(&cgwb_lock);
485         list_del_rcu(&wb->bdi_node);
486         spin_unlock_irq(&cgwb_lock);
487 
488         wb_shutdown(wb);
489 
490         css_put(wb->memcg_css);
491         css_put(wb->blkcg_css);
492 
493         fprop_local_destroy_percpu(&wb->memcg_completions);
494         percpu_ref_exit(&wb->refcnt);
495         wb_exit(wb);
496         kfree_rcu(wb, rcu);
497 
498         if (atomic_dec_and_test(&bdi->usage_cnt))
499                 wake_up_all(&cgwb_release_wait);
500 }
501 
502 static void cgwb_release(struct percpu_ref *refcnt)
503 {
504         struct bdi_writeback *wb = container_of(refcnt, struct bdi_writeback,
505                                                 refcnt);
506         schedule_work(&wb->release_work);
507 }
508 
509 static void cgwb_kill(struct bdi_writeback *wb)
510 {
511         lockdep_assert_held(&cgwb_lock);
512 
513         WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id));
514         list_del(&wb->memcg_node);
515         list_del(&wb->blkcg_node);
516         percpu_ref_kill(&wb->refcnt);
517 }
518 
519 static int cgwb_create(struct backing_dev_info *bdi,
520                        struct cgroup_subsys_state *memcg_css, gfp_t gfp)
521 {
522         struct mem_cgroup *memcg;
523         struct cgroup_subsys_state *blkcg_css;
524         struct blkcg *blkcg;
525         struct list_head *memcg_cgwb_list, *blkcg_cgwb_list;
526         struct bdi_writeback *wb;
527         unsigned long flags;
528         int ret = 0;
529 
530         memcg = mem_cgroup_from_css(memcg_css);
531         blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
532         blkcg = css_to_blkcg(blkcg_css);
533         memcg_cgwb_list = mem_cgroup_cgwb_list(memcg);
534         blkcg_cgwb_list = &blkcg->cgwb_list;
535 
536         /* look up again under lock and discard on blkcg mismatch */
537         spin_lock_irqsave(&cgwb_lock, flags);
538         wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
539         if (wb && wb->blkcg_css != blkcg_css) {
540                 cgwb_kill(wb);
541                 wb = NULL;
542         }
543         spin_unlock_irqrestore(&cgwb_lock, flags);
544         if (wb)
545                 goto out_put;
546 
547         /* need to create a new one */
548         wb = kmalloc(sizeof(*wb), gfp);
549         if (!wb)
550                 return -ENOMEM;
551 
552         ret = wb_init(wb, bdi, blkcg_css->id, gfp);
553         if (ret)
554                 goto err_free;
555 
556         ret = percpu_ref_init(&wb->refcnt, cgwb_release, 0, gfp);
557         if (ret)
558                 goto err_wb_exit;
559 
560         ret = fprop_local_init_percpu(&wb->memcg_completions, gfp);
561         if (ret)
562                 goto err_ref_exit;
563 
564         wb->memcg_css = memcg_css;
565         wb->blkcg_css = blkcg_css;
566         INIT_WORK(&wb->release_work, cgwb_release_workfn);
567         set_bit(WB_registered, &wb->state);
568 
569         /*
570          * The root wb determines the registered state of the whole bdi and
571          * memcg_cgwb_list and blkcg_cgwb_list's next pointers indicate
572          * whether they're still online.  Don't link @wb if any is dead.
573          * See wb_memcg_offline() and wb_blkcg_offline().
574          */
575         ret = -ENODEV;
576         spin_lock_irqsave(&cgwb_lock, flags);
577         if (test_bit(WB_registered, &bdi->wb.state) &&
578             blkcg_cgwb_list->next && memcg_cgwb_list->next) {
579                 /* we might have raced another instance of this function */
580                 ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
581                 if (!ret) {
582                         atomic_inc(&bdi->usage_cnt);
583                         list_add_tail_rcu(&wb->bdi_node, &bdi->wb_list);
584                         list_add(&wb->memcg_node, memcg_cgwb_list);
585                         list_add(&wb->blkcg_node, blkcg_cgwb_list);
586                         css_get(memcg_css);
587                         css_get(blkcg_css);
588                 }
589         }
590         spin_unlock_irqrestore(&cgwb_lock, flags);
591         if (ret) {
592                 if (ret == -EEXIST)
593                         ret = 0;
594                 goto err_fprop_exit;
595         }
596         goto out_put;
597 
598 err_fprop_exit:
599         fprop_local_destroy_percpu(&wb->memcg_completions);
600 err_ref_exit:
601         percpu_ref_exit(&wb->refcnt);
602 err_wb_exit:
603         wb_exit(wb);
604 err_free:
605         kfree(wb);
606 out_put:
607         css_put(blkcg_css);
608         return ret;
609 }
610 
611 /**
612  * wb_get_create - get wb for a given memcg, create if necessary
613  * @bdi: target bdi
614  * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
615  * @gfp: allocation mask to use
616  *
617  * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
618  * create one.  The returned wb has its refcount incremented.
619  *
620  * This function uses css_get() on @memcg_css and thus expects its refcnt
621  * to be positive on invocation.  IOW, rcu_read_lock() protection on
622  * @memcg_css isn't enough.  try_get it before calling this function.
623  *
624  * A wb is keyed by its associated memcg.  As blkcg implicitly enables
625  * memcg on the default hierarchy, memcg association is guaranteed to be
626  * more specific (equal or descendant to the associated blkcg) and thus can
627  * identify both the memcg and blkcg associations.
628  *
629  * Because the blkcg associated with a memcg may change as blkcg is enabled
630  * and disabled closer to root in the hierarchy, each wb keeps track of
631  * both the memcg and blkcg associated with it and verifies the blkcg on
632  * each lookup.  On mismatch, the existing wb is discarded and a new one is
633  * created.
634  */
635 struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
636                                     struct cgroup_subsys_state *memcg_css,
637                                     gfp_t gfp)
638 {
639         struct bdi_writeback *wb;
640 
641         might_sleep_if(gfpflags_allow_blocking(gfp));
642 
643         if (!memcg_css->parent)
644                 return &bdi->wb;
645 
646         do {
647                 rcu_read_lock();
648                 wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
649                 if (wb) {
650                         struct cgroup_subsys_state *blkcg_css;
651 
652                         /* see whether the blkcg association has changed */
653                         blkcg_css = cgroup_get_e_css(memcg_css->cgroup,
654                                                      &io_cgrp_subsys);
655                         if (unlikely(wb->blkcg_css != blkcg_css ||
656                                      !wb_tryget(wb)))
657                                 wb = NULL;
658                         css_put(blkcg_css);
659                 }
660                 rcu_read_unlock();
661         } while (!wb && !cgwb_create(bdi, memcg_css, gfp));
662 
663         return wb;
664 }
665 
666 static int cgwb_bdi_init(struct backing_dev_info *bdi)
667 {
668         int ret;
669 
670         INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);
671         bdi->cgwb_congested_tree = RB_ROOT;
672         atomic_set(&bdi->usage_cnt, 1);
673 
674         ret = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
675         if (!ret) {
676                 bdi->wb.memcg_css = &root_mem_cgroup->css;
677                 bdi->wb.blkcg_css = blkcg_root_css;
678         }
679         return ret;
680 }
681 
682 static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
683 {
684         struct radix_tree_iter iter;
685         struct rb_node *rbn;
686         void **slot;
687 
688         WARN_ON(test_bit(WB_registered, &bdi->wb.state));
689 
690         spin_lock_irq(&cgwb_lock);
691 
692         radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
693                 cgwb_kill(*slot);
694 
695         while ((rbn = rb_first(&bdi->cgwb_congested_tree))) {
696                 struct bdi_writeback_congested *congested =
697                         rb_entry(rbn, struct bdi_writeback_congested, rb_node);
698 
699                 rb_erase(rbn, &bdi->cgwb_congested_tree);
700                 congested->bdi = NULL;  /* mark @congested unlinked */
701         }
702 
703         spin_unlock_irq(&cgwb_lock);
704 
705         /*
706          * All cgwb's and their congested states must be shutdown and
707          * released before returning.  Drain the usage counter to wait for
708          * all cgwb's and cgwb_congested's ever created on @bdi.
709          */
710         atomic_dec(&bdi->usage_cnt);
711         wait_event(cgwb_release_wait, !atomic_read(&bdi->usage_cnt));
712 }
713 
714 /**
715  * wb_memcg_offline - kill all wb's associated with a memcg being offlined
716  * @memcg: memcg being offlined
717  *
718  * Also prevents creation of any new wb's associated with @memcg.
719  */
720 void wb_memcg_offline(struct mem_cgroup *memcg)
721 {
722         LIST_HEAD(to_destroy);
723         struct list_head *memcg_cgwb_list = mem_cgroup_cgwb_list(memcg);
724         struct bdi_writeback *wb, *next;
725 
726         spin_lock_irq(&cgwb_lock);
727         list_for_each_entry_safe(wb, next, memcg_cgwb_list, memcg_node)
728                 cgwb_kill(wb);
729         memcg_cgwb_list->next = NULL;   /* prevent new wb's */
730         spin_unlock_irq(&cgwb_lock);
731 }
732 
733 /**
734  * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
735  * @blkcg: blkcg being offlined
736  *
737  * Also prevents creation of any new wb's associated with @blkcg.
738  */
739 void wb_blkcg_offline(struct blkcg *blkcg)
740 {
741         LIST_HEAD(to_destroy);
742         struct bdi_writeback *wb, *next;
743 
744         spin_lock_irq(&cgwb_lock);
745         list_for_each_entry_safe(wb, next, &blkcg->cgwb_list, blkcg_node)
746                 cgwb_kill(wb);
747         blkcg->cgwb_list.next = NULL;   /* prevent new wb's */
748         spin_unlock_irq(&cgwb_lock);
749 }
750 
751 #else   /* CONFIG_CGROUP_WRITEBACK */
752 
753 static int cgwb_bdi_init(struct backing_dev_info *bdi)
754 {
755         int err;
756 
757         bdi->wb_congested = kzalloc(sizeof(*bdi->wb_congested), GFP_KERNEL);
758         if (!bdi->wb_congested)
759                 return -ENOMEM;
760 
761         err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
762         if (err) {
763                 kfree(bdi->wb_congested);
764                 return err;
765         }
766         return 0;
767 }
768 
769 static void cgwb_bdi_destroy(struct backing_dev_info *bdi) { }
770 
771 #endif  /* CONFIG_CGROUP_WRITEBACK */
772 
773 int bdi_init(struct backing_dev_info *bdi)
774 {
775         int ret;
776 
777         bdi->dev = NULL;
778 
779         bdi->min_ratio = 0;
780         bdi->max_ratio = 100;
781         bdi->max_prop_frac = FPROP_FRAC_BASE;
782         INIT_LIST_HEAD(&bdi->bdi_list);
783         INIT_LIST_HEAD(&bdi->wb_list);
784         init_waitqueue_head(&bdi->wb_waitq);
785 
786         ret = cgwb_bdi_init(bdi);
787 
788         list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
789 
790         return ret;
791 }
792 EXPORT_SYMBOL(bdi_init);
793 
794 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
795                 const char *fmt, ...)
796 {
797         va_list args;
798         struct device *dev;
799 
800         if (bdi->dev)   /* The driver needs to use separate queues per device */
801                 return 0;
802 
803         va_start(args, fmt);
804         dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
805         va_end(args);
806         if (IS_ERR(dev))
807                 return PTR_ERR(dev);
808 
809         bdi->dev = dev;
810 
811         bdi_debug_register(bdi, dev_name(dev));
812         set_bit(WB_registered, &bdi->wb.state);
813 
814         spin_lock_bh(&bdi_lock);
815         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
816         spin_unlock_bh(&bdi_lock);
817 
818         trace_writeback_bdi_register(bdi);
819         return 0;
820 }
821 EXPORT_SYMBOL(bdi_register);
822 
823 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
824 {
825         return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
826 }
827 EXPORT_SYMBOL(bdi_register_dev);
828 
829 int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner)
830 {
831         int rc;
832 
833         rc = bdi_register(bdi, NULL, "%u:%u", MAJOR(owner->devt),
834                         MINOR(owner->devt));
835         if (rc)
836                 return rc;
837         bdi->owner = owner;
838         get_device(owner);
839         return 0;
840 }
841 EXPORT_SYMBOL(bdi_register_owner);
842 
843 /*
844  * Remove bdi from bdi_list, and ensure that it is no longer visible
845  */
846 static void bdi_remove_from_list(struct backing_dev_info *bdi)
847 {
848         spin_lock_bh(&bdi_lock);
849         list_del_rcu(&bdi->bdi_list);
850         spin_unlock_bh(&bdi_lock);
851 
852         synchronize_rcu_expedited();
853 }
854 
855 void bdi_unregister(struct backing_dev_info *bdi)
856 {
857         /* make sure nobody finds us on the bdi_list anymore */
858         bdi_remove_from_list(bdi);
859         wb_shutdown(&bdi->wb);
860         cgwb_bdi_destroy(bdi);
861 
862         if (bdi->dev) {
863                 bdi_debug_unregister(bdi);
864                 device_unregister(bdi->dev);
865                 bdi->dev = NULL;
866         }
867 
868         if (bdi->owner) {
869                 put_device(bdi->owner);
870                 bdi->owner = NULL;
871         }
872 }
873 
874 void bdi_exit(struct backing_dev_info *bdi)
875 {
876         WARN_ON_ONCE(bdi->dev);
877         wb_exit(&bdi->wb);
878 }
879 
880 void bdi_destroy(struct backing_dev_info *bdi)
881 {
882         bdi_unregister(bdi);
883         bdi_exit(bdi);
884 }
885 EXPORT_SYMBOL(bdi_destroy);
886 
887 /*
888  * For use from filesystems to quickly init and register a bdi associated
889  * with dirty writeback
890  */
891 int bdi_setup_and_register(struct backing_dev_info *bdi, char *name)
892 {
893         int err;
894 
895         bdi->name = name;
896         bdi->capabilities = 0;
897         err = bdi_init(bdi);
898         if (err)
899                 return err;
900 
901         err = bdi_register(bdi, NULL, "%.28s-%ld", name,
902                            atomic_long_inc_return(&bdi_seq));
903         if (err) {
904                 bdi_destroy(bdi);
905                 return err;
906         }
907 
908         return 0;
909 }
910 EXPORT_SYMBOL(bdi_setup_and_register);
911 
912 static wait_queue_head_t congestion_wqh[2] = {
913                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
914                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
915         };
916 static atomic_t nr_wb_congested[2];
917 
918 void clear_wb_congested(struct bdi_writeback_congested *congested, int sync)
919 {
920         wait_queue_head_t *wqh = &congestion_wqh[sync];
921         enum wb_congested_state bit;
922 
923         bit = sync ? WB_sync_congested : WB_async_congested;
924         if (test_and_clear_bit(bit, &congested->state))
925                 atomic_dec(&nr_wb_congested[sync]);
926         smp_mb__after_atomic();
927         if (waitqueue_active(wqh))
928                 wake_up(wqh);
929 }
930 EXPORT_SYMBOL(clear_wb_congested);
931 
932 void set_wb_congested(struct bdi_writeback_congested *congested, int sync)
933 {
934         enum wb_congested_state bit;
935 
936         bit = sync ? WB_sync_congested : WB_async_congested;
937         if (!test_and_set_bit(bit, &congested->state))
938                 atomic_inc(&nr_wb_congested[sync]);
939 }
940 EXPORT_SYMBOL(set_wb_congested);
941 
942 /**
943  * congestion_wait - wait for a backing_dev to become uncongested
944  * @sync: SYNC or ASYNC IO
945  * @timeout: timeout in jiffies
946  *
947  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
948  * write congestion.  If no backing_devs are congested then just wait for the
949  * next write to be completed.
950  */
951 long congestion_wait(int sync, long timeout)
952 {
953         long ret;
954         unsigned long start = jiffies;
955         DEFINE_WAIT(wait);
956         wait_queue_head_t *wqh = &congestion_wqh[sync];
957 
958         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
959         ret = io_schedule_timeout(timeout);
960         finish_wait(wqh, &wait);
961 
962         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
963                                         jiffies_to_usecs(jiffies - start));
964 
965         return ret;
966 }
967 EXPORT_SYMBOL(congestion_wait);
968 
969 /**
970  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a pgdat to complete writes
971  * @pgdat: A pgdat to check if it is heavily congested
972  * @sync: SYNC or ASYNC IO
973  * @timeout: timeout in jiffies
974  *
975  * In the event of a congested backing_dev (any backing_dev) and the given
976  * @pgdat has experienced recent congestion, this waits for up to @timeout
977  * jiffies for either a BDI to exit congestion of the given @sync queue
978  * or a write to complete.
979  *
980  * In the absence of pgdat congestion, cond_resched() is called to yield
981  * the processor if necessary but otherwise does not sleep.
982  *
983  * The return value is 0 if the sleep is for the full timeout. Otherwise,
984  * it is the number of jiffies that were still remaining when the function
985  * returned. return_value == timeout implies the function did not sleep.
986  */
987 long wait_iff_congested(struct pglist_data *pgdat, int sync, long timeout)
988 {
989         long ret;
990         unsigned long start = jiffies;
991         DEFINE_WAIT(wait);
992         wait_queue_head_t *wqh = &congestion_wqh[sync];
993 
994         /*
995          * If there is no congestion, or heavy congestion is not being
996          * encountered in the current pgdat, yield if necessary instead
997          * of sleeping on the congestion queue
998          */
999         if (atomic_read(&nr_wb_congested[sync]) == 0 ||
1000             !test_bit(PGDAT_CONGESTED, &pgdat->flags)) {
1001                 cond_resched();
1002 
1003                 /* In case we scheduled, work out time remaining */
1004                 ret = timeout - (jiffies - start);
1005                 if (ret < 0)
1006                         ret = 0;
1007 
1008                 goto out;
1009         }
1010 
1011         /* Sleep until uncongested or a write happens */
1012         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1013         ret = io_schedule_timeout(timeout);
1014         finish_wait(wqh, &wait);
1015 
1016 out:
1017         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
1018                                         jiffies_to_usecs(jiffies - start));
1019 
1020         return ret;
1021 }
1022 EXPORT_SYMBOL(wait_iff_congested);
1023 
1024 int pdflush_proc_obsolete(struct ctl_table *table, int write,
1025                         void __user *buffer, size_t *lenp, loff_t *ppos)
1026 {
1027         char kbuf[] = "\n";
1028 
1029         if (*ppos || *lenp < sizeof(kbuf)) {
1030                 *lenp = 0;
1031                 return 0;
1032         }
1033 
1034         if (copy_to_user(buffer, kbuf, sizeof(kbuf)))
1035                 return -EFAULT;
1036         pr_warn_once("%s exported in /proc is scheduled for removal\n",
1037                      table->procname);
1038 
1039         *lenp = 2;
1040         *ppos += *lenp;
1041         return 2;
1042 }
1043 

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