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 bdi_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_wb_list)
  59                 nr_dirty++;
  60         list_for_each_entry(inode, &wb->b_io, i_wb_list)
  61                 nr_io++;
  62         list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
  63                 nr_more_io++;
  64         list_for_each_entry(inode, &wb->b_dirty_time, i_wb_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         bdi_thresh = wb_dirty_limit(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(bdi_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 int bdi_has_dirty_io(struct backing_dev_info *bdi)
 260 {
 261         return wb_has_dirty_io(&bdi->wb);
 262 }
 263
 264 /*
 265  * This function is used when the first inode for this wb is marked dirty. It
 266  * wakes-up the corresponding bdi thread which should then take care of the
 267  * periodic background write-out of dirty inodes. Since the write-out would
 268  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 269  * set up a timer which wakes the bdi thread up later.
 270  *
 271  * Note, we wouldn't bother setting up the timer, but this function is on the
 272  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 273  * by delaying the wake-up.
 274  *
 275  * We have to be careful not to postpone flush work if it is scheduled for
 276  * earlier. Thus we use queue_delayed_work().
 277  */
 278 void wb_wakeup_delayed(struct bdi_writeback *wb)
 279 {
 280         unsigned long timeout;
 281
 282         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 283         spin_lock_bh(&wb->work_lock);
 284         if (test_bit(WB_registered, &wb->state))
 285                 queue_delayed_work(bdi_wq, &wb->dwork, timeout);
 286         spin_unlock_bh(&wb->work_lock);
 287 }
 288
 289 /*
 290  * Initial write bandwidth: 100 MB/s
 291  */
 292 #define INIT_BW         (100 << (20 - PAGE_SHIFT))
 293
 294 static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 295                    gfp_t gfp)
 296 {
 297         int i, err;
 298
 299         memset(wb, 0, sizeof(*wb));
 300
 301         wb->bdi = bdi;
 302         wb->last_old_flush = jiffies;
 303         INIT_LIST_HEAD(&wb->b_dirty);
 304         INIT_LIST_HEAD(&wb->b_io);
 305         INIT_LIST_HEAD(&wb->b_more_io);
 306         INIT_LIST_HEAD(&wb->b_dirty_time);
 307         spin_lock_init(&wb->list_lock);
 308
 309         wb->bw_time_stamp = jiffies;
 310         wb->balanced_dirty_ratelimit = INIT_BW;
 311         wb->dirty_ratelimit = INIT_BW;
 312         wb->write_bandwidth = INIT_BW;
 313         wb->avg_write_bandwidth = INIT_BW;
 314
 315         spin_lock_init(&wb->work_lock);
 316         INIT_LIST_HEAD(&wb->work_list);
 317         INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
 318
 319         err = fprop_local_init_percpu(&wb->completions, gfp);
 320         if (err)
 321                 return err;
 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                         while (--i)
 327                                 percpu_counter_destroy(&wb->stat[i]);
 328                         fprop_local_destroy_percpu(&wb->completions);
 329                         return err;
 330                 }
 331         }
 332
 333         return 0;
 334 }
 335
 336 /*
 337  * Remove bdi from the global list and shutdown any threads we have running
 338  */
 339 static void wb_shutdown(struct bdi_writeback *wb)
 340 {
 341         /* Make sure nobody queues further work */
 342         spin_lock_bh(&wb->work_lock);
 343         if (!test_and_clear_bit(WB_registered, &wb->state)) {
 344                 spin_unlock_bh(&wb->work_lock);
 345                 return;
 346         }
 347         spin_unlock_bh(&wb->work_lock);
 348
 349         /*
 350          * Drain work list and shutdown the delayed_work.  !WB_registered
 351          * tells wb_workfn() that @wb is dying and its work_list needs to
 352          * be drained no matter what.
 353          */
 354         mod_delayed_work(bdi_wq, &wb->dwork, 0);
 355         flush_delayed_work(&wb->dwork);
 356         WARN_ON(!list_empty(&wb->work_list));
 357 }
 358
 359 static void wb_exit(struct bdi_writeback *wb)
 360 {
 361         int i;
 362
 363         WARN_ON(delayed_work_pending(&wb->dwork));
 364
 365         for (i = 0; i < NR_WB_STAT_ITEMS; i++)
 366                 percpu_counter_destroy(&wb->stat[i]);
 367
 368         fprop_local_destroy_percpu(&wb->completions);
 369 }
 370
 371 #ifdef CONFIG_CGROUP_WRITEBACK
 372
 373 #include <linux/memcontrol.h>
 374
 375 /*
 376  * cgwb_lock protects bdi->cgwb_tree, bdi->cgwb_congested_tree,
 377  * blkcg->cgwb_list, and memcg->cgwb_list.  bdi->cgwb_tree is also RCU
 378  * protected.  cgwb_release_wait is used to wait for the completion of cgwb
 379  * releases from bdi destruction path.
 380  */
 381 static DEFINE_SPINLOCK(cgwb_lock);
 382 static DECLARE_WAIT_QUEUE_HEAD(cgwb_release_wait);
 383
 384 /**
 385  * wb_congested_get_create - get or create a wb_congested
 386  * @bdi: associated bdi
 387  * @blkcg_id: ID of the associated blkcg
 388  * @gfp: allocation mask
 389  *
 390  * Look up the wb_congested for @blkcg_id on @bdi.  If missing, create one.
 391  * The returned wb_congested has its reference count incremented.  Returns
 392  * NULL on failure.
 393  */
 394 struct bdi_writeback_congested *
 395 wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
 396 {
 397         struct bdi_writeback_congested *new_congested = NULL, *congested;
 398         struct rb_node **node, *parent;
 399         unsigned long flags;
 400
 401         if (blkcg_id == 1)
 402                 return &bdi->wb_congested;
 403 retry:
 404         spin_lock_irqsave(&cgwb_lock, flags);
 405
 406         node = &bdi->cgwb_congested_tree.rb_node;
 407         parent = NULL;
 408
 409         while (*node != NULL) {
 410                 parent = *node;
 411                 congested = container_of(parent, struct bdi_writeback_congested,
 412                                          rb_node);
 413                 if (congested->blkcg_id < blkcg_id)
 414                         node = &parent->rb_left;
 415                 else if (congested->blkcg_id > blkcg_id)
 416                         node = &parent->rb_right;
 417                 else
 418                         goto found;
 419         }
 420
 421         if (new_congested) {
 422                 /* !found and storage for new one already allocated, insert */
 423                 congested = new_congested;
 424                 new_congested = NULL;
 425                 rb_link_node(&congested->rb_node, parent, node);
 426                 rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
 427                 atomic_inc(&bdi->usage_cnt);
 428                 goto found;
 429         }
 430
 431         spin_unlock_irqrestore(&cgwb_lock, flags);
 432
 433         /* allocate storage for new one and retry */
 434         new_congested = kzalloc(sizeof(*new_congested), gfp);
 435         if (!new_congested)
 436                 return NULL;
 437
 438         atomic_set(&new_congested->refcnt, 0);
 439         new_congested->bdi = bdi;
 440         new_congested->blkcg_id = blkcg_id;
 441         goto retry;
 442
 443 found:
 444         atomic_inc(&congested->refcnt);
 445         spin_unlock_irqrestore(&cgwb_lock, flags);
 446         kfree(new_congested);
 447         return congested;
 448 }
 449
 450 /**
 451  * wb_congested_put - put a wb_congested
 452  * @congested: wb_congested to put
 453  *
 454  * Put @congested and destroy it if the refcnt reaches zero.
 455  */
 456 void wb_congested_put(struct bdi_writeback_congested *congested)
 457 {
 458         struct backing_dev_info *bdi = congested->bdi;
 459         unsigned long flags;
 460
 461         if (congested->blkcg_id == 1)
 462                 return;
 463
 464         local_irq_save(flags);
 465         if (!atomic_dec_and_lock(&congested->refcnt, &cgwb_lock)) {
 466                 local_irq_restore(flags);
 467                 return;
 468         }
 469
 470         rb_erase(&congested->rb_node, &congested->bdi->cgwb_congested_tree);
 471         spin_unlock_irqrestore(&cgwb_lock, flags);
 472         kfree(congested);
 473
 474         if (atomic_dec_and_test(&bdi->usage_cnt))
 475                 wake_up_all(&cgwb_release_wait);
 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         wb_shutdown(wb);
 485
 486         css_put(wb->memcg_css);
 487         css_put(wb->blkcg_css);
 488         wb_congested_put(wb->congested);
 489
 490         percpu_ref_exit(&wb->refcnt);
 491         wb_exit(wb);
 492         kfree_rcu(wb, rcu);
 493
 494         if (atomic_dec_and_test(&bdi->usage_cnt))
 495                 wake_up_all(&cgwb_release_wait);
 496 }
 497
 498 static void cgwb_release(struct percpu_ref *refcnt)
 499 {
 500         struct bdi_writeback *wb = container_of(refcnt, struct bdi_writeback,
 501                                                 refcnt);
 502         schedule_work(&wb->release_work);
 503 }
 504
 505 static void cgwb_kill(struct bdi_writeback *wb)
 506 {
 507         lockdep_assert_held(&cgwb_lock);
 508
 509         WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id));
 510         list_del(&wb->memcg_node);
 511         list_del(&wb->blkcg_node);
 512         percpu_ref_kill(&wb->refcnt);
 513 }
 514
 515 static int cgwb_create(struct backing_dev_info *bdi,
 516                        struct cgroup_subsys_state *memcg_css, gfp_t gfp)
 517 {
 518         struct mem_cgroup *memcg;
 519         struct cgroup_subsys_state *blkcg_css;
 520         struct blkcg *blkcg;
 521         struct list_head *memcg_cgwb_list, *blkcg_cgwb_list;
 522         struct bdi_writeback *wb;
 523         unsigned long flags;
 524         int ret = 0;
 525
 526         memcg = mem_cgroup_from_css(memcg_css);
 527         blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &blkio_cgrp_subsys);
 528         blkcg = css_to_blkcg(blkcg_css);
 529         memcg_cgwb_list = mem_cgroup_cgwb_list(memcg);
 530         blkcg_cgwb_list = &blkcg->cgwb_list;
 531
 532         /* look up again under lock and discard on blkcg mismatch */
 533         spin_lock_irqsave(&cgwb_lock, flags);
 534         wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
 535         if (wb && wb->blkcg_css != blkcg_css) {
 536                 cgwb_kill(wb);
 537                 wb = NULL;
 538         }
 539         spin_unlock_irqrestore(&cgwb_lock, flags);
 540         if (wb)
 541                 goto out_put;
 542
 543         /* need to create a new one */
 544         wb = kmalloc(sizeof(*wb), gfp);
 545         if (!wb)
 546                 return -ENOMEM;
 547
 548         ret = wb_init(wb, bdi, gfp);
 549         if (ret)
 550                 goto err_free;
 551
 552         ret = percpu_ref_init(&wb->refcnt, cgwb_release, 0, gfp);
 553         if (ret)
 554                 goto err_wb_exit;
 555
 556         wb->congested = wb_congested_get_create(bdi, blkcg_css->id, gfp);
 557         if (!wb->congested)
 558                 goto err_ref_exit;
 559
 560         wb->memcg_css = memcg_css;
 561         wb->blkcg_css = blkcg_css;
 562         INIT_WORK(&wb->release_work, cgwb_release_workfn);
 563         set_bit(WB_registered, &wb->state);
 564
 565         /*
 566          * The root wb determines the registered state of the whole bdi and
 567          * memcg_cgwb_list and blkcg_cgwb_list's next pointers indicate
 568          * whether they're still online.  Don't link @wb if any is dead.
 569          * See wb_memcg_offline() and wb_blkcg_offline().
 570          */
 571         ret = -ENODEV;
 572         spin_lock_irqsave(&cgwb_lock, flags);
 573         if (test_bit(WB_registered, &bdi->wb.state) &&
 574             blkcg_cgwb_list->next && memcg_cgwb_list->next) {
 575                 /* we might have raced another instance of this function */
 576                 ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
 577                 if (!ret) {
 578                         atomic_inc(&bdi->usage_cnt);
 579                         list_add(&wb->memcg_node, memcg_cgwb_list);
 580                         list_add(&wb->blkcg_node, blkcg_cgwb_list);
 581                         css_get(memcg_css);
 582                         css_get(blkcg_css);
 583                 }
 584         }
 585         spin_unlock_irqrestore(&cgwb_lock, flags);
 586         if (ret) {
 587                 if (ret == -EEXIST)
 588                         ret = 0;
 589                 goto err_put_congested;
 590         }
 591         goto out_put;
 592
 593 err_put_congested:
 594         wb_congested_put(wb->congested);
 595 err_ref_exit:
 596         percpu_ref_exit(&wb->refcnt);
 597 err_wb_exit:
 598         wb_exit(wb);
 599 err_free:
 600         kfree(wb);
 601 out_put:
 602         css_put(blkcg_css);
 603         return ret;
 604 }
 605
 606 /**
 607  * wb_get_create - get wb for a given memcg, create if necessary
 608  * @bdi: target bdi
 609  * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
 610  * @gfp: allocation mask to use
 611  *
 612  * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
 613  * create one.  The returned wb has its refcount incremented.
 614  *
 615  * This function uses css_get() on @memcg_css and thus expects its refcnt
 616  * to be positive on invocation.  IOW, rcu_read_lock() protection on
 617  * @memcg_css isn't enough.  try_get it before calling this function.
 618  *
 619  * A wb is keyed by its associated memcg.  As blkcg implicitly enables
 620  * memcg on the default hierarchy, memcg association is guaranteed to be
 621  * more specific (equal or descendant to the associated blkcg) and thus can
 622  * identify both the memcg and blkcg associations.
 623  *
 624  * Because the blkcg associated with a memcg may change as blkcg is enabled
 625  * and disabled closer to root in the hierarchy, each wb keeps track of
 626  * both the memcg and blkcg associated with it and verifies the blkcg on
 627  * each lookup.  On mismatch, the existing wb is discarded and a new one is
 628  * created.
 629  */
 630 struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
 631                                     struct cgroup_subsys_state *memcg_css,
 632                                     gfp_t gfp)
 633 {
 634         struct bdi_writeback *wb;
 635
 636         might_sleep_if(gfp & __GFP_WAIT);
 637
 638         if (!memcg_css->parent)
 639                 return &bdi->wb;
 640
 641         do {
 642                 rcu_read_lock();
 643                 wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
 644                 if (wb) {
 645                         struct cgroup_subsys_state *blkcg_css;
 646
 647                         /* see whether the blkcg association has changed */
 648                         blkcg_css = cgroup_get_e_css(memcg_css->cgroup,
 649                                                      &blkio_cgrp_subsys);
 650                         if (unlikely(wb->blkcg_css != blkcg_css ||
 651                                      !wb_tryget(wb)))
 652                                 wb = NULL;
 653                         css_put(blkcg_css);
 654                 }
 655                 rcu_read_unlock();
 656         } while (!wb && !cgwb_create(bdi, memcg_css, gfp));
 657
 658         return wb;
 659 }
 660
 661 void __inode_attach_wb(struct inode *inode, struct page *page)
 662 {
 663         struct backing_dev_info *bdi = inode_to_bdi(inode);
 664         struct bdi_writeback *wb = NULL;
 665
 666         if (inode_cgwb_enabled(inode)) {
 667                 struct cgroup_subsys_state *memcg_css;
 668
 669                 if (page) {
 670                         memcg_css = mem_cgroup_css_from_page(page);
 671                         wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
 672                 } else {
 673                         /* must pin memcg_css, see wb_get_create() */
 674                         memcg_css = task_get_css(current, memory_cgrp_id);
 675                         wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
 676                         css_put(memcg_css);
 677                 }
 678         }
 679
 680         if (!wb)
 681                 wb = &bdi->wb;
 682
 683         /*
 684          * There may be multiple instances of this function racing to
 685          * update the same inode.  Use cmpxchg() to tell the winner.
 686          */
 687         if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
 688                 wb_put(wb);
 689 }
 690
 691 static void cgwb_bdi_init(struct backing_dev_info *bdi)
 692 {
 693         bdi->wb.memcg_css = mem_cgroup_root_css;
 694         bdi->wb.blkcg_css = blkcg_root_css;
 695         bdi->wb_congested.blkcg_id = 1;
 696         INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);
 697         bdi->cgwb_congested_tree = RB_ROOT;
 698         atomic_set(&bdi->usage_cnt, 1);
 699 }
 700
 701 static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
 702 {
 703         struct radix_tree_iter iter;
 704         void **slot;
 705
 706         WARN_ON(test_bit(WB_registered, &bdi->wb.state));
 707
 708         spin_lock_irq(&cgwb_lock);
 709         radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
 710                 cgwb_kill(*slot);
 711         spin_unlock_irq(&cgwb_lock);
 712
 713         /*
 714          * All cgwb's and their congested states must be shutdown and
 715          * released before returning.  Drain the usage counter to wait for
 716          * all cgwb's and cgwb_congested's ever created on @bdi.
 717          */
 718         atomic_dec(&bdi->usage_cnt);
 719         wait_event(cgwb_release_wait, !atomic_read(&bdi->usage_cnt));
 720 }
 721
 722 /**
 723  * wb_memcg_offline - kill all wb's associated with a memcg being offlined
 724  * @memcg: memcg being offlined
 725  *
 726  * Also prevents creation of any new wb's associated with @memcg.
 727  */
 728 void wb_memcg_offline(struct mem_cgroup *memcg)
 729 {
 730         LIST_HEAD(to_destroy);
 731         struct list_head *memcg_cgwb_list = mem_cgroup_cgwb_list(memcg);
 732         struct bdi_writeback *wb, *next;
 733
 734         spin_lock_irq(&cgwb_lock);
 735         list_for_each_entry_safe(wb, next, memcg_cgwb_list, memcg_node)
 736                 cgwb_kill(wb);
 737         memcg_cgwb_list->next = NULL;   /* prevent new wb's */
 738         spin_unlock_irq(&cgwb_lock);
 739 }
 740
 741 /**
 742  * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
 743  * @blkcg: blkcg being offlined
 744  *
 745  * Also prevents creation of any new wb's associated with @blkcg.
 746  */
 747 void wb_blkcg_offline(struct blkcg *blkcg)
 748 {
 749         LIST_HEAD(to_destroy);
 750         struct bdi_writeback *wb, *next;
 751
 752         spin_lock_irq(&cgwb_lock);
 753         list_for_each_entry_safe(wb, next, &blkcg->cgwb_list, blkcg_node)
 754                 cgwb_kill(wb);
 755         blkcg->cgwb_list.next = NULL;   /* prevent new wb's */
 756         spin_unlock_irq(&cgwb_lock);
 757 }
 758
 759 #else   /* CONFIG_CGROUP_WRITEBACK */
 760
 761 static void cgwb_bdi_init(struct backing_dev_info *bdi) { }
 762 static void cgwb_bdi_destroy(struct backing_dev_info *bdi) { }
 763
 764 #endif  /* CONFIG_CGROUP_WRITEBACK */
 765
 766 int bdi_init(struct backing_dev_info *bdi)
 767 {
 768         int err;
 769
 770         bdi->dev = NULL;
 771
 772         bdi->min_ratio = 0;
 773         bdi->max_ratio = 100;
 774         bdi->max_prop_frac = FPROP_FRAC_BASE;
 775         INIT_LIST_HEAD(&bdi->bdi_list);
 776
 777         err = wb_init(&bdi->wb, bdi, GFP_KERNEL);
 778         if (err)
 779                 return err;
 780
 781         bdi->wb_congested.state = 0;
 782         bdi->wb.congested = &bdi->wb_congested;
 783
 784         cgwb_bdi_init(bdi);
 785         return 0;
 786 }
 787 EXPORT_SYMBOL(bdi_init);
 788
 789 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 790                 const char *fmt, ...)
 791 {
 792         va_list args;
 793         struct device *dev;
 794
 795         if (bdi->dev)   /* The driver needs to use separate queues per device */
 796                 return 0;
 797
 798         va_start(args, fmt);
 799         dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
 800         va_end(args);
 801         if (IS_ERR(dev))
 802                 return PTR_ERR(dev);
 803
 804         bdi->dev = dev;
 805
 806         bdi_debug_register(bdi, dev_name(dev));
 807         set_bit(WB_registered, &bdi->wb.state);
 808
 809         spin_lock_bh(&bdi_lock);
 810         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 811         spin_unlock_bh(&bdi_lock);
 812
 813         trace_writeback_bdi_register(bdi);
 814         return 0;
 815 }
 816 EXPORT_SYMBOL(bdi_register);
 817
 818 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 819 {
 820         return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
 821 }
 822 EXPORT_SYMBOL(bdi_register_dev);
 823
 824 /*
 825  * Remove bdi from bdi_list, and ensure that it is no longer visible
 826  */
 827 static void bdi_remove_from_list(struct backing_dev_info *bdi)
 828 {
 829         spin_lock_bh(&bdi_lock);
 830         list_del_rcu(&bdi->bdi_list);
 831         spin_unlock_bh(&bdi_lock);
 832
 833         synchronize_rcu_expedited();
 834 }
 835
 836 /*
 837  * Called when the device behind @bdi has been removed or ejected.
 838  *
 839  * We can't really do much here except for reducing the dirty ratio at
 840  * the moment.  In the future we should be able to set a flag so that
 841  * the filesystem can handle errors at mark_inode_dirty time instead
 842  * of only at writeback time.
 843  */
 844 void bdi_unregister(struct backing_dev_info *bdi)
 845 {
 846         if (WARN_ON_ONCE(!bdi->dev))
 847                 return;
 848
 849         bdi_set_min_ratio(bdi, 0);
 850 }
 851 EXPORT_SYMBOL(bdi_unregister);
 852
 853 void bdi_destroy(struct backing_dev_info *bdi)
 854 {
 855         /* make sure nobody finds us on the bdi_list anymore */
 856         bdi_remove_from_list(bdi);
 857         wb_shutdown(&bdi->wb);
 858         cgwb_bdi_destroy(bdi);
 859
 860         if (bdi->dev) {
 861                 bdi_debug_unregister(bdi);
 862                 device_unregister(bdi->dev);
 863                 bdi->dev = NULL;
 864         }
 865
 866         wb_exit(&bdi->wb);
 867 }
 868 EXPORT_SYMBOL(bdi_destroy);
 869
 870 /*
 871  * For use from filesystems to quickly init and register a bdi associated
 872  * with dirty writeback
 873  */
 874 int bdi_setup_and_register(struct backing_dev_info *bdi, char *name)
 875 {
 876         int err;
 877
 878         bdi->name = name;
 879         bdi->capabilities = 0;
 880         err = bdi_init(bdi);
 881         if (err)
 882                 return err;
 883
 884         err = bdi_register(bdi, NULL, "%.28s-%ld", name,
 885                            atomic_long_inc_return(&bdi_seq));
 886         if (err) {
 887                 bdi_destroy(bdi);
 888                 return err;
 889         }
 890
 891         return 0;
 892 }
 893 EXPORT_SYMBOL(bdi_setup_and_register);
 894
 895 static wait_queue_head_t congestion_wqh[2] = {
 896                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 897                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 898         };
 899 static atomic_t nr_bdi_congested[2];
 900
 901 void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
 902 {
 903         enum wb_state bit;
 904         wait_queue_head_t *wqh = &congestion_wqh[sync];
 905
 906         bit = sync ? WB_sync_congested : WB_async_congested;
 907         if (test_and_clear_bit(bit, &bdi->wb.congested->state))
 908                 atomic_dec(&nr_bdi_congested[sync]);
 909         smp_mb__after_atomic();
 910         if (waitqueue_active(wqh))
 911                 wake_up(wqh);
 912 }
 913 EXPORT_SYMBOL(clear_bdi_congested);
 914
 915 void set_bdi_congested(struct backing_dev_info *bdi, int sync)
 916 {
 917         enum wb_state bit;
 918
 919         bit = sync ? WB_sync_congested : WB_async_congested;
 920         if (!test_and_set_bit(bit, &bdi->wb.congested->state))
 921                 atomic_inc(&nr_bdi_congested[sync]);
 922 }
 923 EXPORT_SYMBOL(set_bdi_congested);
 924
 925 /**
 926  * congestion_wait - wait for a backing_dev to become uncongested
 927  * @sync: SYNC or ASYNC IO
 928  * @timeout: timeout in jiffies
 929  *
 930  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
 931  * write congestion.  If no backing_devs are congested then just wait for the
 932  * next write to be completed.
 933  */
 934 long congestion_wait(int sync, long timeout)
 935 {
 936         long ret;
 937         unsigned long start = jiffies;
 938         DEFINE_WAIT(wait);
 939         wait_queue_head_t *wqh = &congestion_wqh[sync];
 940
 941         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 942         ret = io_schedule_timeout(timeout);
 943         finish_wait(wqh, &wait);
 944
 945         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
 946                                         jiffies_to_usecs(jiffies - start));
 947
 948         return ret;
 949 }
 950 EXPORT_SYMBOL(congestion_wait);
 951
 952 /**
 953  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
 954  * @zone: A zone to check if it is heavily congested
 955  * @sync: SYNC or ASYNC IO
 956  * @timeout: timeout in jiffies
 957  *
 958  * In the event of a congested backing_dev (any backing_dev) and the given
 959  * @zone has experienced recent congestion, this waits for up to @timeout
 960  * jiffies for either a BDI to exit congestion of the given @sync queue
 961  * or a write to complete.
 962  *
 963  * In the absence of zone congestion, cond_resched() is called to yield
 964  * the processor if necessary but otherwise does not sleep.
 965  *
 966  * The return value is 0 if the sleep is for the full timeout. Otherwise,
 967  * it is the number of jiffies that were still remaining when the function
 968  * returned. return_value == timeout implies the function did not sleep.
 969  */
 970 long wait_iff_congested(struct zone *zone, int sync, long timeout)
 971 {
 972         long ret;
 973         unsigned long start = jiffies;
 974         DEFINE_WAIT(wait);
 975         wait_queue_head_t *wqh = &congestion_wqh[sync];
 976
 977         /*
 978          * If there is no congestion, or heavy congestion is not being
 979          * encountered in the current zone, yield if necessary instead
 980          * of sleeping on the congestion queue
 981          */
 982         if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
 983             !test_bit(ZONE_CONGESTED, &zone->flags)) {
 984                 cond_resched();
 985
 986                 /* In case we scheduled, work out time remaining */
 987                 ret = timeout - (jiffies - start);
 988                 if (ret < 0)
 989                         ret = 0;
 990
 991                 goto out;
 992         }
 993
 994         /* Sleep until uncongested or a write happens */
 995         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 996         ret = io_schedule_timeout(timeout);
 997         finish_wait(wqh, &wait);
 998
 999 out:
1000         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
1001                                         jiffies_to_usecs(jiffies - start));
1002
1003         return ret;
1004 }
1005 EXPORT_SYMBOL(wait_iff_congested);
1006
1007 int pdflush_proc_obsolete(struct ctl_table *table, int write,
1008                         void __user *buffer, size_t *lenp, loff_t *ppos)
1009 {
1010         char kbuf[] = "0\n";
1011
1012         if (*ppos || *lenp < sizeof(kbuf)) {
1013                 *lenp = 0;
1014                 return 0;
1015         }
1016
1017         if (copy_to_user(buffer, kbuf, sizeof(kbuf)))
1018                 return -EFAULT;
1019         printk_once(KERN_WARNING "%s exported in /proc is scheduled for removal\n",
1020                         table->procname);
1021
1022         *lenp = 2;
1023         *ppos += *lenp;
1024         return 2;
1025 }