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 struct backing_dev_info noop_backing_dev_info = {
  16         .name           = "noop",
  17         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
  18 };
  19 EXPORT_SYMBOL_GPL(noop_backing_dev_info);
  20
  21 static struct class *bdi_class;
  22
  23 /*
  24  * bdi_lock protects updates to bdi_list. bdi_list has RCU reader side
  25  * locking.
  26  */
  27 DEFINE_SPINLOCK(bdi_lock);
  28 LIST_HEAD(bdi_list);
  29
  30 /* bdi_wq serves all asynchronous writeback tasks */
  31 struct workqueue_struct *bdi_wq;
  32
  33 #ifdef CONFIG_DEBUG_FS
  34 #include <linux/debugfs.h>
  35 #include <linux/seq_file.h>
  36
  37 static struct dentry *bdi_debug_root;
  38
  39 static void bdi_debug_init(void)
  40 {
  41         bdi_debug_root = debugfs_create_dir("bdi", NULL);
  42 }
  43
  44 static int bdi_debug_stats_show(struct seq_file *m, void *v)
  45 {
  46         struct backing_dev_info *bdi = m->private;
  47         struct bdi_writeback *wb = &bdi->wb;
  48         unsigned long background_thresh;
  49         unsigned long dirty_thresh;
  50         unsigned long wb_thresh;
  51         unsigned long nr_dirty, nr_io, nr_more_io, nr_dirty_time;
  52         struct inode *inode;
  53
  54         nr_dirty = nr_io = nr_more_io = nr_dirty_time = 0;
  55         spin_lock(&wb->list_lock);
  56         list_for_each_entry(inode, &wb->b_dirty, i_io_list)
  57                 nr_dirty++;
  58         list_for_each_entry(inode, &wb->b_io, i_io_list)
  59                 nr_io++;
  60         list_for_each_entry(inode, &wb->b_more_io, i_io_list)
  61                 nr_more_io++;
  62         list_for_each_entry(inode, &wb->b_dirty_time, i_io_list)
  63                 if (inode->i_state & I_DIRTY_TIME)
  64                         nr_dirty_time++;
  65         spin_unlock(&wb->list_lock);
  66
  67         global_dirty_limits(&background_thresh, &dirty_thresh);
  68         wb_thresh = wb_calc_thresh(wb, dirty_thresh);
  69
  70 #define K(x) ((x) << (PAGE_SHIFT - 10))
  71         seq_printf(m,
  72                    "BdiWriteback:       %10lu kB\n"
  73                    "BdiReclaimable:     %10lu kB\n"
  74                    "BdiDirtyThresh:     %10lu kB\n"
  75                    "DirtyThresh:        %10lu kB\n"
  76                    "BackgroundThresh:   %10lu kB\n"
  77                    "BdiDirtied:         %10lu kB\n"
  78                    "BdiWritten:         %10lu kB\n"
  79                    "BdiWriteBandwidth:  %10lu kBps\n"
  80                    "b_dirty:            %10lu\n"
  81                    "b_io:               %10lu\n"
  82                    "b_more_io:          %10lu\n"
  83                    "b_dirty_time:       %10lu\n"
  84                    "bdi_list:           %10u\n"
  85                    "state:              %10lx\n",
  86                    (unsigned long) K(wb_stat(wb, WB_WRITEBACK)),
  87                    (unsigned long) K(wb_stat(wb, WB_RECLAIMABLE)),
  88                    K(wb_thresh),
  89                    K(dirty_thresh),
  90                    K(background_thresh),
  91                    (unsigned long) K(wb_stat(wb, WB_DIRTIED)),
  92                    (unsigned long) K(wb_stat(wb, WB_WRITTEN)),
  93                    (unsigned long) K(wb->write_bandwidth),
  94                    nr_dirty,
  95                    nr_io,
  96                    nr_more_io,
  97                    nr_dirty_time,
  98                    !list_empty(&bdi->bdi_list), bdi->wb.state);
  99 #undef K
 100
 101         return 0;
 102 }
 103 DEFINE_SHOW_ATTRIBUTE(bdi_debug_stats);
 104
 105 static int bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 106 {
 107         if (!bdi_debug_root)
 108                 return -ENOMEM;
 109
 110         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
 111         if (!bdi->debug_dir)
 112                 return -ENOMEM;
 113
 114         bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
 115                                                bdi, &bdi_debug_stats_fops);
 116         if (!bdi->debug_stats) {
 117                 debugfs_remove(bdi->debug_dir);
 118                 bdi->debug_dir = NULL;
 119                 return -ENOMEM;
 120         }
 121
 122         return 0;
 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 int bdi_debug_register(struct backing_dev_info *bdi,
 135                                       const char *name)
 136 {
 137         return 0;
 138 }
 139 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 140 {
 141 }
 142 #endif
 143
 144 static ssize_t read_ahead_kb_store(struct device *dev,
 145                                   struct device_attribute *attr,
 146                                   const char *buf, size_t count)
 147 {
 148         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 149         unsigned long read_ahead_kb;
 150         ssize_t ret;
 151
 152         ret = kstrtoul(buf, 10, &read_ahead_kb);
 153         if (ret < 0)
 154                 return ret;
 155
 156         bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
 157
 158         return count;
 159 }
 160
 161 #define K(pages) ((pages) << (PAGE_SHIFT - 10))
 162
 163 #define BDI_SHOW(name, expr)                                            \
 164 static ssize_t name##_show(struct device *dev,                          \
 165                            struct device_attribute *attr, char *page)   \
 166 {                                                                       \
 167         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
 168                                                                         \
 169         return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
 170 }                                                                       \
 171 static DEVICE_ATTR_RW(name);
 172
 173 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 174
 175 static ssize_t min_ratio_store(struct device *dev,
 176                 struct device_attribute *attr, const char *buf, size_t count)
 177 {
 178         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 179         unsigned int ratio;
 180         ssize_t ret;
 181
 182         ret = kstrtouint(buf, 10, &ratio);
 183         if (ret < 0)
 184                 return ret;
 185
 186         ret = bdi_set_min_ratio(bdi, ratio);
 187         if (!ret)
 188                 ret = count;
 189
 190         return ret;
 191 }
 192 BDI_SHOW(min_ratio, bdi->min_ratio)
 193
 194 static ssize_t max_ratio_store(struct device *dev,
 195                 struct device_attribute *attr, const char *buf, size_t count)
 196 {
 197         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 198         unsigned int ratio;
 199         ssize_t ret;
 200
 201         ret = kstrtouint(buf, 10, &ratio);
 202         if (ret < 0)
 203                 return ret;
 204
 205         ret = bdi_set_max_ratio(bdi, ratio);
 206         if (!ret)
 207                 ret = count;
 208
 209         return ret;
 210 }
 211 BDI_SHOW(max_ratio, bdi->max_ratio)
 212
 213 static ssize_t stable_pages_required_show(struct device *dev,
 214                                           struct device_attribute *attr,
 215                                           char *page)
 216 {
 217         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 218
 219         return snprintf(page, PAGE_SIZE-1, "%d\n",
 220                         bdi_cap_stable_pages_required(bdi) ? 1 : 0);
 221 }
 222 static DEVICE_ATTR_RO(stable_pages_required);
 223
 224 static struct attribute *bdi_dev_attrs[] = {
 225         &dev_attr_read_ahead_kb.attr,
 226         &dev_attr_min_ratio.attr,
 227         &dev_attr_max_ratio.attr,
 228         &dev_attr_stable_pages_required.attr,
 229         NULL,
 230 };
 231 ATTRIBUTE_GROUPS(bdi_dev);
 232
 233 static __init int bdi_class_init(void)
 234 {
 235         bdi_class = class_create(THIS_MODULE, "bdi");
 236         if (IS_ERR(bdi_class))
 237                 return PTR_ERR(bdi_class);
 238
 239         bdi_class->dev_groups = bdi_dev_groups;
 240         bdi_debug_init();
 241
 242         return 0;
 243 }
 244 postcore_initcall(bdi_class_init);
 245
 246 static int bdi_init(struct backing_dev_info *bdi);
 247
 248 static int __init default_bdi_init(void)
 249 {
 250         int err;
 251
 252         bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE |
 253                                               WQ_UNBOUND | WQ_SYSFS, 0);
 254         if (!bdi_wq)
 255                 return -ENOMEM;
 256
 257         err = bdi_init(&noop_backing_dev_info);
 258
 259         return err;
 260 }
 261 subsys_initcall(default_bdi_init);
 262
 263 /*
 264  * This function is used when the first inode for this wb is marked dirty. It
 265  * wakes-up the corresponding bdi thread which should then take care of the
 266  * periodic background write-out of dirty inodes. Since the write-out would
 267  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 268  * set up a timer which wakes the bdi thread up later.
 269  *
 270  * Note, we wouldn't bother setting up the timer, but this function is on the
 271  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 272  * by delaying the wake-up.
 273  *
 274  * We have to be careful not to postpone flush work if it is scheduled for
 275  * earlier. Thus we use queue_delayed_work().
 276  */
 277 void wb_wakeup_delayed(struct bdi_writeback *wb)
 278 {
 279         unsigned long timeout;
 280
 281         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 282         spin_lock_bh(&wb->work_lock);
 283         if (test_bit(WB_registered, &wb->state))
 284                 queue_delayed_work(bdi_wq, &wb->dwork, timeout);
 285         spin_unlock_bh(&wb->work_lock);
 286 }
 287
 288 /*
 289  * Initial write bandwidth: 100 MB/s
 290  */
 291 #define INIT_BW         (100 << (20 - PAGE_SHIFT))
 292
 293 static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 294                    int blkcg_id, gfp_t gfp)
 295 {
 296         int i, err;
 297
 298         memset(wb, 0, sizeof(*wb));
 299
 300         if (wb != &bdi->wb)
 301                 bdi_get(bdi);
 302         wb->bdi = bdi;
 303         wb->last_old_flush = jiffies;
 304         INIT_LIST_HEAD(&wb->b_dirty);
 305         INIT_LIST_HEAD(&wb->b_io);
 306         INIT_LIST_HEAD(&wb->b_more_io);
 307         INIT_LIST_HEAD(&wb->b_dirty_time);
 308         spin_lock_init(&wb->list_lock);
 309
 310         wb->bw_time_stamp = jiffies;
 311         wb->balanced_dirty_ratelimit = INIT_BW;
 312         wb->dirty_ratelimit = INIT_BW;
 313         wb->write_bandwidth = INIT_BW;
 314         wb->avg_write_bandwidth = INIT_BW;
 315
 316         spin_lock_init(&wb->work_lock);
 317         INIT_LIST_HEAD(&wb->work_list);
 318         INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
 319         wb->dirty_sleep = jiffies;
 320
 321         wb->congested = wb_congested_get_create(bdi, blkcg_id, gfp);
 322         if (!wb->congested) {
 323                 err = -ENOMEM;
 324                 goto out_put_bdi;
 325         }
 326
 327         err = fprop_local_init_percpu(&wb->completions, gfp);
 328         if (err)
 329                 goto out_put_cong;
 330
 331         for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
 332                 err = percpu_counter_init(&wb->stat[i], 0, gfp);
 333                 if (err)
 334                         goto out_destroy_stat;
 335         }
 336
 337         return 0;
 338
 339 out_destroy_stat:
 340         while (i--)
 341                 percpu_counter_destroy(&wb->stat[i]);
 342         fprop_local_destroy_percpu(&wb->completions);
 343 out_put_cong:
 344         wb_congested_put(wb->congested);
 345 out_put_bdi:
 346         if (wb != &bdi->wb)
 347                 bdi_put(bdi);
 348         return err;
 349 }
 350
 351 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb);
 352
 353 /*
 354  * Remove bdi from the global list and shutdown any threads we have running
 355  */
 356 static void wb_shutdown(struct bdi_writeback *wb)
 357 {
 358         /* Make sure nobody queues further work */
 359         spin_lock_bh(&wb->work_lock);
 360         if (!test_and_clear_bit(WB_registered, &wb->state)) {
 361                 spin_unlock_bh(&wb->work_lock);
 362                 return;
 363         }
 364         spin_unlock_bh(&wb->work_lock);
 365
 366         cgwb_remove_from_bdi_list(wb);
 367         /*
 368          * Drain work list and shutdown the delayed_work.  !WB_registered
 369          * tells wb_workfn() that @wb is dying and its work_list needs to
 370          * be drained no matter what.
 371          */
 372         mod_delayed_work(bdi_wq, &wb->dwork, 0);
 373         flush_delayed_work(&wb->dwork);
 374         WARN_ON(!list_empty(&wb->work_list));
 375 }
 376
 377 static void wb_exit(struct bdi_writeback *wb)
 378 {
 379         int i;
 380
 381         WARN_ON(delayed_work_pending(&wb->dwork));
 382
 383         for (i = 0; i < NR_WB_STAT_ITEMS; i++)
 384                 percpu_counter_destroy(&wb->stat[i]);
 385
 386         fprop_local_destroy_percpu(&wb->completions);
 387         wb_congested_put(wb->congested);
 388         if (wb != &wb->bdi->wb)
 389                 bdi_put(wb->bdi);
 390 }
 391
 392 #ifdef CONFIG_CGROUP_WRITEBACK
 393
 394 #include <linux/memcontrol.h>
 395
 396 /*
 397  * cgwb_lock protects bdi->cgwb_tree, bdi->cgwb_congested_tree,
 398  * blkcg->cgwb_list, and memcg->cgwb_list.  bdi->cgwb_tree is also RCU
 399  * protected.
 400  */
 401 static DEFINE_SPINLOCK(cgwb_lock);
 402 static struct workqueue_struct *cgwb_release_wq;
 403
 404 /**
 405  * wb_congested_get_create - get or create a wb_congested
 406  * @bdi: associated bdi
 407  * @blkcg_id: ID of the associated blkcg
 408  * @gfp: allocation mask
 409  *
 410  * Look up the wb_congested for @blkcg_id on @bdi.  If missing, create one.
 411  * The returned wb_congested has its reference count incremented.  Returns
 412  * NULL on failure.
 413  */
 414 struct bdi_writeback_congested *
 415 wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
 416 {
 417         struct bdi_writeback_congested *new_congested = NULL, *congested;
 418         struct rb_node **node, *parent;
 419         unsigned long flags;
 420 retry:
 421         spin_lock_irqsave(&cgwb_lock, flags);
 422
 423         node = &bdi->cgwb_congested_tree.rb_node;
 424         parent = NULL;
 425
 426         while (*node != NULL) {
 427                 parent = *node;
 428                 congested = rb_entry(parent, struct bdi_writeback_congested,
 429                                      rb_node);
 430                 if (congested->blkcg_id < blkcg_id)
 431                         node = &parent->rb_left;
 432                 else if (congested->blkcg_id > blkcg_id)
 433                         node = &parent->rb_right;
 434                 else
 435                         goto found;
 436         }
 437
 438         if (new_congested) {
 439                 /* !found and storage for new one already allocated, insert */
 440                 congested = new_congested;
 441                 new_congested = NULL;
 442                 rb_link_node(&congested->rb_node, parent, node);
 443                 rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
 444                 goto found;
 445         }
 446
 447         spin_unlock_irqrestore(&cgwb_lock, flags);
 448
 449         /* allocate storage for new one and retry */
 450         new_congested = kzalloc(sizeof(*new_congested), gfp);
 451         if (!new_congested)
 452                 return NULL;
 453
 454         atomic_set(&new_congested->refcnt, 0);
 455         new_congested->__bdi = bdi;
 456         new_congested->blkcg_id = blkcg_id;
 457         goto retry;
 458
 459 found:
 460         atomic_inc(&congested->refcnt);
 461         spin_unlock_irqrestore(&cgwb_lock, flags);
 462         kfree(new_congested);
 463         return congested;
 464 }
 465
 466 /**
 467  * wb_congested_put - put a wb_congested
 468  * @congested: wb_congested to put
 469  *
 470  * Put @congested and destroy it if the refcnt reaches zero.
 471  */
 472 void wb_congested_put(struct bdi_writeback_congested *congested)
 473 {
 474         unsigned long flags;
 475
 476         local_irq_save(flags);
 477         if (!atomic_dec_and_lock(&congested->refcnt, &cgwb_lock)) {
 478                 local_irq_restore(flags);
 479                 return;
 480         }
 481
 482         /* bdi might already have been destroyed leaving @congested unlinked */
 483         if (congested->__bdi) {
 484                 rb_erase(&congested->rb_node,
 485                          &congested->__bdi->cgwb_congested_tree);
 486                 congested->__bdi = NULL;
 487         }
 488
 489         spin_unlock_irqrestore(&cgwb_lock, flags);
 490         kfree(congested);
 491 }
 492
 493 static void cgwb_release_workfn(struct work_struct *work)
 494 {
 495         struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
 496                                                 release_work);
 497
 498         mutex_lock(&wb->bdi->cgwb_release_mutex);
 499         wb_shutdown(wb);
 500
 501         css_put(wb->memcg_css);
 502         css_put(wb->blkcg_css);
 503         mutex_unlock(&wb->bdi->cgwb_release_mutex);
 504
 505         fprop_local_destroy_percpu(&wb->memcg_completions);
 506         percpu_ref_exit(&wb->refcnt);
 507         wb_exit(wb);
 508         kfree_rcu(wb, rcu);
 509 }
 510
 511 static void cgwb_release(struct percpu_ref *refcnt)
 512 {
 513         struct bdi_writeback *wb = container_of(refcnt, struct bdi_writeback,
 514                                                 refcnt);
 515         queue_work(cgwb_release_wq, &wb->release_work);
 516 }
 517
 518 static void cgwb_kill(struct bdi_writeback *wb)
 519 {
 520         lockdep_assert_held(&cgwb_lock);
 521
 522         WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id));
 523         list_del(&wb->memcg_node);
 524         list_del(&wb->blkcg_node);
 525         percpu_ref_kill(&wb->refcnt);
 526 }
 527
 528 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
 529 {
 530         spin_lock_irq(&cgwb_lock);
 531         list_del_rcu(&wb->bdi_node);
 532         spin_unlock_irq(&cgwb_lock);
 533 }
 534
 535 static int cgwb_create(struct backing_dev_info *bdi,
 536                        struct cgroup_subsys_state *memcg_css, gfp_t gfp)
 537 {
 538         struct mem_cgroup *memcg;
 539         struct cgroup_subsys_state *blkcg_css;
 540         struct blkcg *blkcg;
 541         struct list_head *memcg_cgwb_list, *blkcg_cgwb_list;
 542         struct bdi_writeback *wb;
 543         unsigned long flags;
 544         int ret = 0;
 545
 546         memcg = mem_cgroup_from_css(memcg_css);
 547         blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
 548         blkcg = css_to_blkcg(blkcg_css);
 549         memcg_cgwb_list = &memcg->cgwb_list;
 550         blkcg_cgwb_list = &blkcg->cgwb_list;
 551
 552         /* look up again under lock and discard on blkcg mismatch */
 553         spin_lock_irqsave(&cgwb_lock, flags);
 554         wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
 555         if (wb && wb->blkcg_css != blkcg_css) {
 556                 cgwb_kill(wb);
 557                 wb = NULL;
 558         }
 559         spin_unlock_irqrestore(&cgwb_lock, flags);
 560         if (wb)
 561                 goto out_put;
 562
 563         /* need to create a new one */
 564         wb = kmalloc(sizeof(*wb), gfp);
 565         if (!wb) {
 566                 ret = -ENOMEM;
 567                 goto out_put;
 568         }
 569
 570         ret = wb_init(wb, bdi, blkcg_css->id, gfp);
 571         if (ret)
 572                 goto err_free;
 573
 574         ret = percpu_ref_init(&wb->refcnt, cgwb_release, 0, gfp);
 575         if (ret)
 576                 goto err_wb_exit;
 577
 578         ret = fprop_local_init_percpu(&wb->memcg_completions, gfp);
 579         if (ret)
 580                 goto err_ref_exit;
 581
 582         wb->memcg_css = memcg_css;
 583         wb->blkcg_css = blkcg_css;
 584         INIT_WORK(&wb->release_work, cgwb_release_workfn);
 585         set_bit(WB_registered, &wb->state);
 586
 587         /*
 588          * The root wb determines the registered state of the whole bdi and
 589          * memcg_cgwb_list and blkcg_cgwb_list's next pointers indicate
 590          * whether they're still online.  Don't link @wb if any is dead.
 591          * See wb_memcg_offline() and wb_blkcg_offline().
 592          */
 593         ret = -ENODEV;
 594         spin_lock_irqsave(&cgwb_lock, flags);
 595         if (test_bit(WB_registered, &bdi->wb.state) &&
 596             blkcg_cgwb_list->next && memcg_cgwb_list->next) {
 597                 /* we might have raced another instance of this function */
 598                 ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
 599                 if (!ret) {
 600                         list_add_tail_rcu(&wb->bdi_node, &bdi->wb_list);
 601                         list_add(&wb->memcg_node, memcg_cgwb_list);
 602                         list_add(&wb->blkcg_node, blkcg_cgwb_list);
 603                         css_get(memcg_css);
 604                         css_get(blkcg_css);
 605                 }
 606         }
 607         spin_unlock_irqrestore(&cgwb_lock, flags);
 608         if (ret) {
 609                 if (ret == -EEXIST)
 610                         ret = 0;
 611                 goto err_fprop_exit;
 612         }
 613         goto out_put;
 614
 615 err_fprop_exit:
 616         fprop_local_destroy_percpu(&wb->memcg_completions);
 617 err_ref_exit:
 618         percpu_ref_exit(&wb->refcnt);
 619 err_wb_exit:
 620         wb_exit(wb);
 621 err_free:
 622         kfree(wb);
 623 out_put:
 624         css_put(blkcg_css);
 625         return ret;
 626 }
 627
 628 /**
 629  * wb_get_create - get wb for a given memcg, create if necessary
 630  * @bdi: target bdi
 631  * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
 632  * @gfp: allocation mask to use
 633  *
 634  * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
 635  * create one.  The returned wb has its refcount incremented.
 636  *
 637  * This function uses css_get() on @memcg_css and thus expects its refcnt
 638  * to be positive on invocation.  IOW, rcu_read_lock() protection on
 639  * @memcg_css isn't enough.  try_get it before calling this function.
 640  *
 641  * A wb is keyed by its associated memcg.  As blkcg implicitly enables
 642  * memcg on the default hierarchy, memcg association is guaranteed to be
 643  * more specific (equal or descendant to the associated blkcg) and thus can
 644  * identify both the memcg and blkcg associations.
 645  *
 646  * Because the blkcg associated with a memcg may change as blkcg is enabled
 647  * and disabled closer to root in the hierarchy, each wb keeps track of
 648  * both the memcg and blkcg associated with it and verifies the blkcg on
 649  * each lookup.  On mismatch, the existing wb is discarded and a new one is
 650  * created.
 651  */
 652 struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
 653                                     struct cgroup_subsys_state *memcg_css,
 654                                     gfp_t gfp)
 655 {
 656         struct bdi_writeback *wb;
 657
 658         might_sleep_if(gfpflags_allow_blocking(gfp));
 659
 660         if (!memcg_css->parent)
 661                 return &bdi->wb;
 662
 663         do {
 664                 rcu_read_lock();
 665                 wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
 666                 if (wb) {
 667                         struct cgroup_subsys_state *blkcg_css;
 668
 669                         /* see whether the blkcg association has changed */
 670                         blkcg_css = cgroup_get_e_css(memcg_css->cgroup,
 671                                                      &io_cgrp_subsys);
 672                         if (unlikely(wb->blkcg_css != blkcg_css ||
 673                                      !wb_tryget(wb)))
 674                                 wb = NULL;
 675                         css_put(blkcg_css);
 676                 }
 677                 rcu_read_unlock();
 678         } while (!wb && !cgwb_create(bdi, memcg_css, gfp));
 679
 680         return wb;
 681 }
 682
 683 static int cgwb_bdi_init(struct backing_dev_info *bdi)
 684 {
 685         int ret;
 686
 687         INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);
 688         bdi->cgwb_congested_tree = RB_ROOT;
 689         mutex_init(&bdi->cgwb_release_mutex);
 690
 691         ret = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
 692         if (!ret) {
 693                 bdi->wb.memcg_css = &root_mem_cgroup->css;
 694                 bdi->wb.blkcg_css = blkcg_root_css;
 695         }
 696         return ret;
 697 }
 698
 699 static void cgwb_bdi_unregister(struct backing_dev_info *bdi)
 700 {
 701         struct radix_tree_iter iter;
 702         void **slot;
 703         struct bdi_writeback *wb;
 704
 705         WARN_ON(test_bit(WB_registered, &bdi->wb.state));
 706
 707         spin_lock_irq(&cgwb_lock);
 708         radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
 709                 cgwb_kill(*slot);
 710         spin_unlock_irq(&cgwb_lock);
 711
 712         mutex_lock(&bdi->cgwb_release_mutex);
 713         spin_lock_irq(&cgwb_lock);
 714         while (!list_empty(&bdi->wb_list)) {
 715                 wb = list_first_entry(&bdi->wb_list, struct bdi_writeback,
 716                                       bdi_node);
 717                 spin_unlock_irq(&cgwb_lock);
 718                 wb_shutdown(wb);
 719                 spin_lock_irq(&cgwb_lock);
 720         }
 721         spin_unlock_irq(&cgwb_lock);
 722         mutex_unlock(&bdi->cgwb_release_mutex);
 723 }
 724
 725 /**
 726  * wb_memcg_offline - kill all wb's associated with a memcg being offlined
 727  * @memcg: memcg being offlined
 728  *
 729  * Also prevents creation of any new wb's associated with @memcg.
 730  */
 731 void wb_memcg_offline(struct mem_cgroup *memcg)
 732 {
 733         struct list_head *memcg_cgwb_list = &memcg->cgwb_list;
 734         struct bdi_writeback *wb, *next;
 735
 736         spin_lock_irq(&cgwb_lock);
 737         list_for_each_entry_safe(wb, next, memcg_cgwb_list, memcg_node)
 738                 cgwb_kill(wb);
 739         memcg_cgwb_list->next = NULL;   /* prevent new wb's */
 740         spin_unlock_irq(&cgwb_lock);
 741 }
 742
 743 /**
 744  * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
 745  * @blkcg: blkcg being offlined
 746  *
 747  * Also prevents creation of any new wb's associated with @blkcg.
 748  */
 749 void wb_blkcg_offline(struct blkcg *blkcg)
 750 {
 751         struct bdi_writeback *wb, *next;
 752
 753         spin_lock_irq(&cgwb_lock);
 754         list_for_each_entry_safe(wb, next, &blkcg->cgwb_list, blkcg_node)
 755                 cgwb_kill(wb);
 756         blkcg->cgwb_list.next = NULL;   /* prevent new wb's */
 757         spin_unlock_irq(&cgwb_lock);
 758 }
 759
 760 static void cgwb_bdi_exit(struct backing_dev_info *bdi)
 761 {
 762         struct rb_node *rbn;
 763
 764         spin_lock_irq(&cgwb_lock);
 765         while ((rbn = rb_first(&bdi->cgwb_congested_tree))) {
 766                 struct bdi_writeback_congested *congested =
 767                         rb_entry(rbn, struct bdi_writeback_congested, rb_node);
 768
 769                 rb_erase(rbn, &bdi->cgwb_congested_tree);
 770                 congested->__bdi = NULL;        /* mark @congested unlinked */
 771         }
 772         spin_unlock_irq(&cgwb_lock);
 773 }
 774
 775 static void cgwb_bdi_register(struct backing_dev_info *bdi)
 776 {
 777         spin_lock_irq(&cgwb_lock);
 778         list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
 779         spin_unlock_irq(&cgwb_lock);
 780 }
 781
 782 static int __init cgwb_init(void)
 783 {
 784         /*
 785          * There can be many concurrent release work items overwhelming
 786          * system_wq.  Put them in a separate wq and limit concurrency.
 787          * There's no point in executing many of these in parallel.
 788          */
 789         cgwb_release_wq = alloc_workqueue("cgwb_release", 0, 1);
 790         if (!cgwb_release_wq)
 791                 return -ENOMEM;
 792
 793         return 0;
 794 }
 795 subsys_initcall(cgwb_init);
 796
 797 #else   /* CONFIG_CGROUP_WRITEBACK */
 798
 799 static int cgwb_bdi_init(struct backing_dev_info *bdi)
 800 {
 801         int err;
 802
 803         bdi->wb_congested = kzalloc(sizeof(*bdi->wb_congested), GFP_KERNEL);
 804         if (!bdi->wb_congested)
 805                 return -ENOMEM;
 806
 807         atomic_set(&bdi->wb_congested->refcnt, 1);
 808
 809         err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
 810         if (err) {
 811                 wb_congested_put(bdi->wb_congested);
 812                 return err;
 813         }
 814         return 0;
 815 }
 816
 817 static void cgwb_bdi_unregister(struct backing_dev_info *bdi) { }
 818
 819 static void cgwb_bdi_exit(struct backing_dev_info *bdi)
 820 {
 821         wb_congested_put(bdi->wb_congested);
 822 }
 823
 824 static void cgwb_bdi_register(struct backing_dev_info *bdi)
 825 {
 826         list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
 827 }
 828
 829 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
 830 {
 831         list_del_rcu(&wb->bdi_node);
 832 }
 833
 834 #endif  /* CONFIG_CGROUP_WRITEBACK */
 835
 836 static int bdi_init(struct backing_dev_info *bdi)
 837 {
 838         int ret;
 839
 840         bdi->dev = NULL;
 841
 842         kref_init(&bdi->refcnt);
 843         bdi->min_ratio = 0;
 844         bdi->max_ratio = 100;
 845         bdi->max_prop_frac = FPROP_FRAC_BASE;
 846         INIT_LIST_HEAD(&bdi->bdi_list);
 847         INIT_LIST_HEAD(&bdi->wb_list);
 848         init_waitqueue_head(&bdi->wb_waitq);
 849
 850         ret = cgwb_bdi_init(bdi);
 851
 852         return ret;
 853 }
 854
 855 struct backing_dev_info *bdi_alloc_node(gfp_t gfp_mask, int node_id)
 856 {
 857         struct backing_dev_info *bdi;
 858
 859         bdi = kmalloc_node(sizeof(struct backing_dev_info),
 860                            gfp_mask | __GFP_ZERO, node_id);
 861         if (!bdi)
 862                 return NULL;
 863
 864         if (bdi_init(bdi)) {
 865                 kfree(bdi);
 866                 return NULL;
 867         }
 868         return bdi;
 869 }
 870 EXPORT_SYMBOL(bdi_alloc_node);
 871
 872 int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
 873 {
 874         struct device *dev;
 875
 876         if (bdi->dev)   /* The driver needs to use separate queues per device */
 877                 return 0;
 878
 879         dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args);
 880         if (IS_ERR(dev))
 881                 return PTR_ERR(dev);
 882
 883         cgwb_bdi_register(bdi);
 884         bdi->dev = dev;
 885
 886         bdi_debug_register(bdi, dev_name(dev));
 887         set_bit(WB_registered, &bdi->wb.state);
 888
 889         spin_lock_bh(&bdi_lock);
 890         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 891         spin_unlock_bh(&bdi_lock);
 892
 893         trace_writeback_bdi_register(bdi);
 894         return 0;
 895 }
 896 EXPORT_SYMBOL(bdi_register_va);
 897
 898 int bdi_register(struct backing_dev_info *bdi, const char *fmt, ...)
 899 {
 900         va_list args;
 901         int ret;
 902
 903         va_start(args, fmt);
 904         ret = bdi_register_va(bdi, fmt, args);
 905         va_end(args);
 906         return ret;
 907 }
 908 EXPORT_SYMBOL(bdi_register);
 909
 910 int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner)
 911 {
 912         int rc;
 913
 914         rc = bdi_register(bdi, "%u:%u", MAJOR(owner->devt), MINOR(owner->devt));
 915         if (rc)
 916                 return rc;
 917         /* Leaking owner reference... */
 918         WARN_ON(bdi->owner);
 919         bdi->owner = owner;
 920         get_device(owner);
 921         return 0;
 922 }
 923 EXPORT_SYMBOL(bdi_register_owner);
 924
 925 /*
 926  * Remove bdi from bdi_list, and ensure that it is no longer visible
 927  */
 928 static void bdi_remove_from_list(struct backing_dev_info *bdi)
 929 {
 930         spin_lock_bh(&bdi_lock);
 931         list_del_rcu(&bdi->bdi_list);
 932         spin_unlock_bh(&bdi_lock);
 933
 934         synchronize_rcu_expedited();
 935 }
 936
 937 void bdi_unregister(struct backing_dev_info *bdi)
 938 {
 939         /* make sure nobody finds us on the bdi_list anymore */
 940         bdi_remove_from_list(bdi);
 941         wb_shutdown(&bdi->wb);
 942         cgwb_bdi_unregister(bdi);
 943
 944         if (bdi->dev) {
 945                 bdi_debug_unregister(bdi);
 946                 device_unregister(bdi->dev);
 947                 bdi->dev = NULL;
 948         }
 949
 950         if (bdi->owner) {
 951                 put_device(bdi->owner);
 952                 bdi->owner = NULL;
 953         }
 954 }
 955
 956 static void release_bdi(struct kref *ref)
 957 {
 958         struct backing_dev_info *bdi =
 959                         container_of(ref, struct backing_dev_info, refcnt);
 960
 961         if (test_bit(WB_registered, &bdi->wb.state))
 962                 bdi_unregister(bdi);
 963         WARN_ON_ONCE(bdi->dev);
 964         wb_exit(&bdi->wb);
 965         cgwb_bdi_exit(bdi);
 966         kfree(bdi);
 967 }
 968
 969 void bdi_put(struct backing_dev_info *bdi)
 970 {
 971         kref_put(&bdi->refcnt, release_bdi);
 972 }
 973 EXPORT_SYMBOL(bdi_put);
 974
 975 static wait_queue_head_t congestion_wqh[2] = {
 976                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 977                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 978         };
 979 static atomic_t nr_wb_congested[2];
 980
 981 void clear_wb_congested(struct bdi_writeback_congested *congested, int sync)
 982 {
 983         wait_queue_head_t *wqh = &congestion_wqh[sync];
 984         enum wb_congested_state bit;
 985
 986         bit = sync ? WB_sync_congested : WB_async_congested;
 987         if (test_and_clear_bit(bit, &congested->state))
 988                 atomic_dec(&nr_wb_congested[sync]);
 989         smp_mb__after_atomic();
 990         if (waitqueue_active(wqh))
 991                 wake_up(wqh);
 992 }
 993 EXPORT_SYMBOL(clear_wb_congested);
 994
 995 void set_wb_congested(struct bdi_writeback_congested *congested, int sync)
 996 {
 997         enum wb_congested_state bit;
 998
 999         bit = sync ? WB_sync_congested : WB_async_congested;
1000         if (!test_and_set_bit(bit, &congested->state))
1001                 atomic_inc(&nr_wb_congested[sync]);
1002 }
1003 EXPORT_SYMBOL(set_wb_congested);
1004
1005 /**
1006  * congestion_wait - wait for a backing_dev to become uncongested
1007  * @sync: SYNC or ASYNC IO
1008  * @timeout: timeout in jiffies
1009  *
1010  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
1011  * write congestion.  If no backing_devs are congested then just wait for the
1012  * next write to be completed.
1013  */
1014 long congestion_wait(int sync, long timeout)
1015 {
1016         long ret;
1017         unsigned long start = jiffies;
1018         DEFINE_WAIT(wait);
1019         wait_queue_head_t *wqh = &congestion_wqh[sync];
1020
1021         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1022         ret = io_schedule_timeout(timeout);
1023         finish_wait(wqh, &wait);
1024
1025         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
1026                                         jiffies_to_usecs(jiffies - start));
1027
1028         return ret;
1029 }
1030 EXPORT_SYMBOL(congestion_wait);
1031
1032 /**
1033  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a pgdat to complete writes
1034  * @sync: SYNC or ASYNC IO
1035  * @timeout: timeout in jiffies
1036  *
1037  * In the event of a congested backing_dev (any backing_dev) this waits
1038  * for up to @timeout jiffies for either a BDI to exit congestion of the
1039  * given @sync queue or a write to complete.
1040  *
1041  * The return value is 0 if the sleep is for the full timeout. Otherwise,
1042  * it is the number of jiffies that were still remaining when the function
1043  * returned. return_value == timeout implies the function did not sleep.
1044  */
1045 long wait_iff_congested(int sync, long timeout)
1046 {
1047         long ret;
1048         unsigned long start = jiffies;
1049         DEFINE_WAIT(wait);
1050         wait_queue_head_t *wqh = &congestion_wqh[sync];
1051
1052         /*
1053          * If there is no congestion, yield if necessary instead
1054          * of sleeping on the congestion queue
1055          */
1056         if (atomic_read(&nr_wb_congested[sync]) == 0) {
1057                 cond_resched();
1058
1059                 /* In case we scheduled, work out time remaining */
1060                 ret = timeout - (jiffies - start);
1061                 if (ret < 0)
1062                         ret = 0;
1063
1064                 goto out;
1065         }
1066
1067         /* Sleep until uncongested or a write happens */
1068         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1069         ret = io_schedule_timeout(timeout);
1070         finish_wait(wqh, &wait);
1071
1072 out:
1073         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
1074                                         jiffies_to_usecs(jiffies - start));
1075
1076         return ret;
1077 }
1078 EXPORT_SYMBOL(wait_iff_congested);