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 default_backing_dev_info = {
  18         .name           = "default",
  19         .ra_pages       = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
  20         .state          = 0,
  21         .capabilities   = BDI_CAP_MAP_COPY,
  22 };
  23 EXPORT_SYMBOL_GPL(default_backing_dev_info);
  24
  25 struct backing_dev_info noop_backing_dev_info = {
  26         .name           = "noop",
  27         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
  28 };
  29 EXPORT_SYMBOL_GPL(noop_backing_dev_info);
  30
  31 static struct class *bdi_class;
  32
  33 /*
  34  * bdi_lock protects updates to bdi_list and bdi_pending_list, as well as
  35  * reader side protection for bdi_pending_list. bdi_list has RCU reader side
  36  * locking.
  37  */
  38 DEFINE_SPINLOCK(bdi_lock);
  39 LIST_HEAD(bdi_list);
  40 LIST_HEAD(bdi_pending_list);
  41
  42 static struct task_struct *sync_supers_tsk;
  43 static struct timer_list sync_supers_timer;
  44
  45 static int bdi_sync_supers(void *);
  46 static void sync_supers_timer_fn(unsigned long);
  47
  48 void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
  49 {
  50         if (wb1 < wb2) {
  51                 spin_lock(&wb1->list_lock);
  52                 spin_lock_nested(&wb2->list_lock, 1);
  53         } else {
  54                 spin_lock(&wb2->list_lock);
  55                 spin_lock_nested(&wb1->list_lock, 1);
  56         }
  57 }
  58
  59 #ifdef CONFIG_DEBUG_FS
  60 #include <linux/debugfs.h>
  61 #include <linux/seq_file.h>
  62
  63 static struct dentry *bdi_debug_root;
  64
  65 static void bdi_debug_init(void)
  66 {
  67         bdi_debug_root = debugfs_create_dir("bdi", NULL);
  68 }
  69
  70 static int bdi_debug_stats_show(struct seq_file *m, void *v)
  71 {
  72         struct backing_dev_info *bdi = m->private;
  73         struct bdi_writeback *wb = &bdi->wb;
  74         unsigned long background_thresh;
  75         unsigned long dirty_thresh;
  76         unsigned long bdi_thresh;
  77         unsigned long nr_dirty, nr_io, nr_more_io;
  78         struct inode *inode;
  79
  80         nr_dirty = nr_io = nr_more_io = 0;
  81         spin_lock(&wb->list_lock);
  82         list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
  83                 nr_dirty++;
  84         list_for_each_entry(inode, &wb->b_io, i_wb_list)
  85                 nr_io++;
  86         list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
  87                 nr_more_io++;
  88         spin_unlock(&wb->list_lock);
  89
  90         global_dirty_limits(&background_thresh, &dirty_thresh);
  91         bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
  92
  93 #define K(x) ((x) << (PAGE_SHIFT - 10))
  94         seq_printf(m,
  95                    "BdiWriteback:       %10lu kB\n"
  96                    "BdiReclaimable:     %10lu kB\n"
  97                    "BdiDirtyThresh:     %10lu kB\n"
  98                    "DirtyThresh:        %10lu kB\n"
  99                    "BackgroundThresh:   %10lu kB\n"
 100                    "BdiWritten:         %10lu kB\n"
 101                    "BdiWriteBandwidth:  %10lu kBps\n"
 102                    "b_dirty:            %10lu\n"
 103                    "b_io:               %10lu\n"
 104                    "b_more_io:          %10lu\n"
 105                    "bdi_list:           %10u\n"
 106                    "state:              %10lx\n",
 107                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
 108                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
 109                    K(bdi_thresh),
 110                    K(dirty_thresh),
 111                    K(background_thresh),
 112                    (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
 113                    (unsigned long) K(bdi->write_bandwidth),
 114                    nr_dirty,
 115                    nr_io,
 116                    nr_more_io,
 117                    !list_empty(&bdi->bdi_list), bdi->state);
 118 #undef K
 119
 120         return 0;
 121 }
 122
 123 static int bdi_debug_stats_open(struct inode *inode, struct file *file)
 124 {
 125         return single_open(file, bdi_debug_stats_show, inode->i_private);
 126 }
 127
 128 static const struct file_operations bdi_debug_stats_fops = {
 129         .open           = bdi_debug_stats_open,
 130         .read           = seq_read,
 131         .llseek         = seq_lseek,
 132         .release        = single_release,
 133 };
 134
 135 static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 136 {
 137         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
 138         bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
 139                                                bdi, &bdi_debug_stats_fops);
 140 }
 141
 142 static void bdi_debug_unregister(struct backing_dev_info *bdi)
 143 {
 144         debugfs_remove(bdi->debug_stats);
 145         debugfs_remove(bdi->debug_dir);
 146 }
 147 #else
 148 static inline void bdi_debug_init(void)
 149 {
 150 }
 151 static inline void bdi_debug_register(struct backing_dev_info *bdi,
 152                                       const char *name)
 153 {
 154 }
 155 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 156 {
 157 }
 158 #endif
 159
 160 static ssize_t read_ahead_kb_store(struct device *dev,
 161                                   struct device_attribute *attr,
 162                                   const char *buf, size_t count)
 163 {
 164         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 165         char *end;
 166         unsigned long read_ahead_kb;
 167         ssize_t ret = -EINVAL;
 168
 169         read_ahead_kb = simple_strtoul(buf, &end, 10);
 170         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 171                 bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
 172                 ret = count;
 173         }
 174         return ret;
 175 }
 176
 177 #define K(pages) ((pages) << (PAGE_SHIFT - 10))
 178
 179 #define BDI_SHOW(name, expr)                                            \
 180 static ssize_t name##_show(struct device *dev,                          \
 181                            struct device_attribute *attr, char *page)   \
 182 {                                                                       \
 183         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
 184                                                                         \
 185         return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
 186 }
 187
 188 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 189
 190 static ssize_t min_ratio_store(struct device *dev,
 191                 struct device_attribute *attr, const char *buf, size_t count)
 192 {
 193         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 194         char *end;
 195         unsigned int ratio;
 196         ssize_t ret = -EINVAL;
 197
 198         ratio = simple_strtoul(buf, &end, 10);
 199         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 200                 ret = bdi_set_min_ratio(bdi, ratio);
 201                 if (!ret)
 202                         ret = count;
 203         }
 204         return ret;
 205 }
 206 BDI_SHOW(min_ratio, bdi->min_ratio)
 207
 208 static ssize_t max_ratio_store(struct device *dev,
 209                 struct device_attribute *attr, const char *buf, size_t count)
 210 {
 211         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 212         char *end;
 213         unsigned int ratio;
 214         ssize_t ret = -EINVAL;
 215
 216         ratio = simple_strtoul(buf, &end, 10);
 217         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 218                 ret = bdi_set_max_ratio(bdi, ratio);
 219                 if (!ret)
 220                         ret = count;
 221         }
 222         return ret;
 223 }
 224 BDI_SHOW(max_ratio, bdi->max_ratio)
 225
 226 #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
 227
 228 static struct device_attribute bdi_dev_attrs[] = {
 229         __ATTR_RW(read_ahead_kb),
 230         __ATTR_RW(min_ratio),
 231         __ATTR_RW(max_ratio),
 232         __ATTR_NULL,
 233 };
 234
 235 static __init int bdi_class_init(void)
 236 {
 237         bdi_class = class_create(THIS_MODULE, "bdi");
 238         if (IS_ERR(bdi_class))
 239                 return PTR_ERR(bdi_class);
 240
 241         bdi_class->dev_attrs = bdi_dev_attrs;
 242         bdi_debug_init();
 243         return 0;
 244 }
 245 postcore_initcall(bdi_class_init);
 246
 247 static int __init default_bdi_init(void)
 248 {
 249         int err;
 250
 251         sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
 252         BUG_ON(IS_ERR(sync_supers_tsk));
 253
 254         setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
 255         bdi_arm_supers_timer();
 256
 257         err = bdi_init(&default_backing_dev_info);
 258         if (!err)
 259                 bdi_register(&default_backing_dev_info, NULL, "default");
 260         err = bdi_init(&noop_backing_dev_info);
 261
 262         return err;
 263 }
 264 subsys_initcall(default_bdi_init);
 265
 266 int bdi_has_dirty_io(struct backing_dev_info *bdi)
 267 {
 268         return wb_has_dirty_io(&bdi->wb);
 269 }
 270
 271 /*
 272  * kupdated() used to do this. We cannot do it from the bdi_forker_thread()
 273  * or we risk deadlocking on ->s_umount. The longer term solution would be
 274  * to implement sync_supers_bdi() or similar and simply do it from the
 275  * bdi writeback thread individually.
 276  */
 277 static int bdi_sync_supers(void *unused)
 278 {
 279         set_user_nice(current, 0);
 280
 281         while (!kthread_should_stop()) {
 282                 set_current_state(TASK_INTERRUPTIBLE);
 283                 schedule();
 284
 285                 /*
 286                  * Do this periodically, like kupdated() did before.
 287                  */
 288                 sync_supers();
 289         }
 290
 291         return 0;
 292 }
 293
 294 void bdi_arm_supers_timer(void)
 295 {
 296         unsigned long next;
 297
 298         if (!dirty_writeback_interval)
 299                 return;
 300
 301         next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies;
 302         mod_timer(&sync_supers_timer, round_jiffies_up(next));
 303 }
 304
 305 static void sync_supers_timer_fn(unsigned long unused)
 306 {
 307         wake_up_process(sync_supers_tsk);
 308         bdi_arm_supers_timer();
 309 }
 310
 311 static void wakeup_timer_fn(unsigned long data)
 312 {
 313         struct backing_dev_info *bdi = (struct backing_dev_info *)data;
 314
 315         spin_lock_bh(&bdi->wb_lock);
 316         if (bdi->wb.task) {
 317                 trace_writeback_wake_thread(bdi);
 318                 wake_up_process(bdi->wb.task);
 319         } else {
 320                 /*
 321                  * When bdi tasks are inactive for long time, they are killed.
 322                  * In this case we have to wake-up the forker thread which
 323                  * should create and run the bdi thread.
 324                  */
 325                 trace_writeback_wake_forker_thread(bdi);
 326                 wake_up_process(default_backing_dev_info.wb.task);
 327         }
 328         spin_unlock_bh(&bdi->wb_lock);
 329 }
 330
 331 /*
 332  * This function is used when the first inode for this bdi is marked dirty. It
 333  * wakes-up the corresponding bdi thread which should then take care of the
 334  * periodic background write-out of dirty inodes. Since the write-out would
 335  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 336  * set up a timer which wakes the bdi thread up later.
 337  *
 338  * Note, we wouldn't bother setting up the timer, but this function is on the
 339  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 340  * by delaying the wake-up.
 341  */
 342 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
 343 {
 344         unsigned long timeout;
 345
 346         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 347         mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
 348 }
 349
 350 /*
 351  * Calculate the longest interval (jiffies) bdi threads are allowed to be
 352  * inactive.
 353  */
 354 static unsigned long bdi_longest_inactive(void)
 355 {
 356         unsigned long interval;
 357
 358         interval = msecs_to_jiffies(dirty_writeback_interval * 10);
 359         return max(5UL * 60 * HZ, interval);
 360 }
 361
 362 static int bdi_forker_thread(void *ptr)
 363 {
 364         struct bdi_writeback *me = ptr;
 365
 366         current->flags |= PF_SWAPWRITE;
 367         set_freezable();
 368
 369         /*
 370          * Our parent may run at a different priority, just set us to normal
 371          */
 372         set_user_nice(current, 0);
 373
 374         for (;;) {
 375                 struct task_struct *task = NULL;
 376                 struct backing_dev_info *bdi;
 377                 enum {
 378                         NO_ACTION,   /* Nothing to do */
 379                         FORK_THREAD, /* Fork bdi thread */
 380                         KILL_THREAD, /* Kill inactive bdi thread */
 381                 } action = NO_ACTION;
 382
 383                 /*
 384                  * Temporary measure, we want to make sure we don't see
 385                  * dirty data on the default backing_dev_info
 386                  */
 387                 if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
 388                         del_timer(&me->wakeup_timer);
 389                         wb_do_writeback(me, 0);
 390                 }
 391
 392                 spin_lock_bh(&bdi_lock);
 393                 set_current_state(TASK_INTERRUPTIBLE);
 394
 395                 list_for_each_entry(bdi, &bdi_list, bdi_list) {
 396                         bool have_dirty_io;
 397
 398                         if (!bdi_cap_writeback_dirty(bdi) ||
 399                              bdi_cap_flush_forker(bdi))
 400                                 continue;
 401
 402                         WARN(!test_bit(BDI_registered, &bdi->state),
 403                              "bdi %p/%s is not registered!\n", bdi, bdi->name);
 404
 405                         have_dirty_io = !list_empty(&bdi->work_list) ||
 406                                         wb_has_dirty_io(&bdi->wb);
 407
 408                         /*
 409                          * If the bdi has work to do, but the thread does not
 410                          * exist - create it.
 411                          */
 412                         if (!bdi->wb.task && have_dirty_io) {
 413                                 /*
 414                                  * Set the pending bit - if someone will try to
 415                                  * unregister this bdi - it'll wait on this bit.
 416                                  */
 417                                 set_bit(BDI_pending, &bdi->state);
 418                                 action = FORK_THREAD;
 419                                 break;
 420                         }
 421
 422                         spin_lock(&bdi->wb_lock);
 423
 424                         /*
 425                          * If there is no work to do and the bdi thread was
 426                          * inactive long enough - kill it. The wb_lock is taken
 427                          * to make sure no-one adds more work to this bdi and
 428                          * wakes the bdi thread up.
 429                          */
 430                         if (bdi->wb.task && !have_dirty_io &&
 431                             time_after(jiffies, bdi->wb.last_active +
 432                                                 bdi_longest_inactive())) {
 433                                 task = bdi->wb.task;
 434                                 bdi->wb.task = NULL;
 435                                 spin_unlock(&bdi->wb_lock);
 436                                 set_bit(BDI_pending, &bdi->state);
 437                                 action = KILL_THREAD;
 438                                 break;
 439                         }
 440                         spin_unlock(&bdi->wb_lock);
 441                 }
 442                 spin_unlock_bh(&bdi_lock);
 443
 444                 /* Keep working if default bdi still has things to do */
 445                 if (!list_empty(&me->bdi->work_list))
 446                         __set_current_state(TASK_RUNNING);
 447
 448                 switch (action) {
 449                 case FORK_THREAD:
 450                         __set_current_state(TASK_RUNNING);
 451                         task = kthread_create(bdi_writeback_thread, &bdi->wb,
 452                                               "flush-%s", dev_name(bdi->dev));
 453                         if (IS_ERR(task)) {
 454                                 /*
 455                                  * If thread creation fails, force writeout of
 456                                  * the bdi from the thread. Hopefully 1024 is
 457                                  * large enough for efficient IO.
 458                                  */
 459                                 writeback_inodes_wb(&bdi->wb, 1024);
 460                         } else {
 461                                 /*
 462                                  * The spinlock makes sure we do not lose
 463                                  * wake-ups when racing with 'bdi_queue_work()'.
 464                                  * And as soon as the bdi thread is visible, we
 465                                  * can start it.
 466                                  */
 467                                 spin_lock_bh(&bdi->wb_lock);
 468                                 bdi->wb.task = task;
 469                                 spin_unlock_bh(&bdi->wb_lock);
 470                                 wake_up_process(task);
 471                         }
 472                         break;
 473
 474                 case KILL_THREAD:
 475                         __set_current_state(TASK_RUNNING);
 476                         kthread_stop(task);
 477                         break;
 478
 479                 case NO_ACTION:
 480                         if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
 481                                 /*
 482                                  * There are no dirty data. The only thing we
 483                                  * should now care about is checking for
 484                                  * inactive bdi threads and killing them. Thus,
 485                                  * let's sleep for longer time, save energy and
 486                                  * be friendly for battery-driven devices.
 487                                  */
 488                                 schedule_timeout(bdi_longest_inactive());
 489                         else
 490                                 schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
 491                         try_to_freeze();
 492                         /* Back to the main loop */
 493                         continue;
 494                 }
 495
 496                 /*
 497                  * Clear pending bit and wakeup anybody waiting to tear us down.
 498                  */
 499                 clear_bit(BDI_pending, &bdi->state);
 500                 smp_mb__after_clear_bit();
 501                 wake_up_bit(&bdi->state, BDI_pending);
 502         }
 503
 504         return 0;
 505 }
 506
 507 /*
 508  * Remove bdi from bdi_list, and ensure that it is no longer visible
 509  */
 510 static void bdi_remove_from_list(struct backing_dev_info *bdi)
 511 {
 512         spin_lock_bh(&bdi_lock);
 513         list_del_rcu(&bdi->bdi_list);
 514         spin_unlock_bh(&bdi_lock);
 515
 516         synchronize_rcu_expedited();
 517 }
 518
 519 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 520                 const char *fmt, ...)
 521 {
 522         va_list args;
 523         struct device *dev;
 524
 525         if (bdi->dev)   /* The driver needs to use separate queues per device */
 526                 return 0;
 527
 528         va_start(args, fmt);
 529         dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
 530         va_end(args);
 531         if (IS_ERR(dev))
 532                 return PTR_ERR(dev);
 533
 534         bdi->dev = dev;
 535
 536         /*
 537          * Just start the forker thread for our default backing_dev_info,
 538          * and add other bdi's to the list. They will get a thread created
 539          * on-demand when they need it.
 540          */
 541         if (bdi_cap_flush_forker(bdi)) {
 542                 struct bdi_writeback *wb = &bdi->wb;
 543
 544                 wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
 545                                                 dev_name(dev));
 546                 if (IS_ERR(wb->task))
 547                         return PTR_ERR(wb->task);
 548         }
 549
 550         bdi_debug_register(bdi, dev_name(dev));
 551         set_bit(BDI_registered, &bdi->state);
 552
 553         spin_lock_bh(&bdi_lock);
 554         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 555         spin_unlock_bh(&bdi_lock);
 556
 557         trace_writeback_bdi_register(bdi);
 558         return 0;
 559 }
 560 EXPORT_SYMBOL(bdi_register);
 561
 562 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 563 {
 564         return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
 565 }
 566 EXPORT_SYMBOL(bdi_register_dev);
 567
 568 /*
 569  * Remove bdi from the global list and shutdown any threads we have running
 570  */
 571 static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 572 {
 573         if (!bdi_cap_writeback_dirty(bdi))
 574                 return;
 575
 576         /*
 577          * Make sure nobody finds us on the bdi_list anymore
 578          */
 579         bdi_remove_from_list(bdi);
 580
 581         /*
 582          * If setup is pending, wait for that to complete first
 583          */
 584         wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
 585                         TASK_UNINTERRUPTIBLE);
 586
 587         /*
 588          * Finally, kill the kernel thread. We don't need to be RCU
 589          * safe anymore, since the bdi is gone from visibility. Force
 590          * unfreeze of the thread before calling kthread_stop(), otherwise
 591          * it would never exet if it is currently stuck in the refrigerator.
 592          */
 593         if (bdi->wb.task) {
 594                 thaw_process(bdi->wb.task);
 595                 kthread_stop(bdi->wb.task);
 596         }
 597 }
 598
 599 /*
 600  * This bdi is going away now, make sure that no super_blocks point to it
 601  */
 602 static void bdi_prune_sb(struct backing_dev_info *bdi)
 603 {
 604         struct super_block *sb;
 605
 606         spin_lock(&sb_lock);
 607         list_for_each_entry(sb, &super_blocks, s_list) {
 608                 if (sb->s_bdi == bdi)
 609                         sb->s_bdi = &default_backing_dev_info;
 610         }
 611         spin_unlock(&sb_lock);
 612 }
 613
 614 void bdi_unregister(struct backing_dev_info *bdi)
 615 {
 616         if (bdi->dev) {
 617                 bdi_set_min_ratio(bdi, 0);
 618                 trace_writeback_bdi_unregister(bdi);
 619                 bdi_prune_sb(bdi);
 620                 del_timer_sync(&bdi->wb.wakeup_timer);
 621
 622                 if (!bdi_cap_flush_forker(bdi))
 623                         bdi_wb_shutdown(bdi);
 624                 bdi_debug_unregister(bdi);
 625                 device_unregister(bdi->dev);
 626                 bdi->dev = NULL;
 627         }
 628 }
 629 EXPORT_SYMBOL(bdi_unregister);
 630
 631 static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 632 {
 633         memset(wb, 0, sizeof(*wb));
 634
 635         wb->bdi = bdi;
 636         wb->last_old_flush = jiffies;
 637         INIT_LIST_HEAD(&wb->b_dirty);
 638         INIT_LIST_HEAD(&wb->b_io);
 639         INIT_LIST_HEAD(&wb->b_more_io);
 640         spin_lock_init(&wb->list_lock);
 641         setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
 642 }
 643
 644 /*
 645  * Initial write bandwidth: 100 MB/s
 646  */
 647 #define INIT_BW         (100 << (20 - PAGE_SHIFT))
 648
 649 int bdi_init(struct backing_dev_info *bdi)
 650 {
 651         int i, err;
 652
 653         bdi->dev = NULL;
 654
 655         bdi->min_ratio = 0;
 656         bdi->max_ratio = 100;
 657         bdi->max_prop_frac = PROP_FRAC_BASE;
 658         spin_lock_init(&bdi->wb_lock);
 659         INIT_LIST_HEAD(&bdi->bdi_list);
 660         INIT_LIST_HEAD(&bdi->work_list);
 661
 662         bdi_wb_init(&bdi->wb, bdi);
 663
 664         for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 665                 err = percpu_counter_init(&bdi->bdi_stat[i], 0);
 666                 if (err)
 667                         goto err;
 668         }
 669
 670         bdi->dirty_exceeded = 0;
 671
 672         bdi->bw_time_stamp = jiffies;
 673         bdi->written_stamp = 0;
 674
 675         bdi->write_bandwidth = INIT_BW;
 676         bdi->avg_write_bandwidth = INIT_BW;
 677
 678         err = prop_local_init_percpu(&bdi->completions);
 679
 680         if (err) {
 681 err:
 682                 while (i--)
 683                         percpu_counter_destroy(&bdi->bdi_stat[i]);
 684         }
 685
 686         return err;
 687 }
 688 EXPORT_SYMBOL(bdi_init);
 689
 690 void bdi_destroy(struct backing_dev_info *bdi)
 691 {
 692         int i;
 693
 694         /*
 695          * Splice our entries to the default_backing_dev_info, if this
 696          * bdi disappears
 697          */
 698         if (bdi_has_dirty_io(bdi)) {
 699                 struct bdi_writeback *dst = &default_backing_dev_info.wb;
 700
 701                 bdi_lock_two(&bdi->wb, dst);
 702                 list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
 703                 list_splice(&bdi->wb.b_io, &dst->b_io);
 704                 list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
 705                 spin_unlock(&bdi->wb.list_lock);
 706                 spin_unlock(&dst->list_lock);
 707         }
 708
 709         bdi_unregister(bdi);
 710
 711         for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 712                 percpu_counter_destroy(&bdi->bdi_stat[i]);
 713
 714         prop_local_destroy_percpu(&bdi->completions);
 715 }
 716 EXPORT_SYMBOL(bdi_destroy);
 717
 718 /*
 719  * For use from filesystems to quickly init and register a bdi associated
 720  * with dirty writeback
 721  */
 722 int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
 723                            unsigned int cap)
 724 {
 725         char tmp[32];
 726         int err;
 727
 728         bdi->name = name;
 729         bdi->capabilities = cap;
 730         err = bdi_init(bdi);
 731         if (err)
 732                 return err;
 733
 734         sprintf(tmp, "%.28s%s", name, "-%d");
 735         err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq));
 736         if (err) {
 737                 bdi_destroy(bdi);
 738                 return err;
 739         }
 740
 741         return 0;
 742 }
 743 EXPORT_SYMBOL(bdi_setup_and_register);
 744
 745 static wait_queue_head_t congestion_wqh[2] = {
 746                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 747                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 748         };
 749 static atomic_t nr_bdi_congested[2];
 750
 751 void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
 752 {
 753         enum bdi_state bit;
 754         wait_queue_head_t *wqh = &congestion_wqh[sync];
 755
 756         bit = sync ? BDI_sync_congested : BDI_async_congested;
 757         if (test_and_clear_bit(bit, &bdi->state))
 758                 atomic_dec(&nr_bdi_congested[sync]);
 759         smp_mb__after_clear_bit();
 760         if (waitqueue_active(wqh))
 761                 wake_up(wqh);
 762 }
 763 EXPORT_SYMBOL(clear_bdi_congested);
 764
 765 void set_bdi_congested(struct backing_dev_info *bdi, int sync)
 766 {
 767         enum bdi_state bit;
 768
 769         bit = sync ? BDI_sync_congested : BDI_async_congested;
 770         if (!test_and_set_bit(bit, &bdi->state))
 771                 atomic_inc(&nr_bdi_congested[sync]);
 772 }
 773 EXPORT_SYMBOL(set_bdi_congested);
 774
 775 /**
 776  * congestion_wait - wait for a backing_dev to become uncongested
 777  * @sync: SYNC or ASYNC IO
 778  * @timeout: timeout in jiffies
 779  *
 780  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
 781  * write congestion.  If no backing_devs are congested then just wait for the
 782  * next write to be completed.
 783  */
 784 long congestion_wait(int sync, long timeout)
 785 {
 786         long ret;
 787         unsigned long start = jiffies;
 788         DEFINE_WAIT(wait);
 789         wait_queue_head_t *wqh = &congestion_wqh[sync];
 790
 791         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 792         ret = io_schedule_timeout(timeout);
 793         finish_wait(wqh, &wait);
 794
 795         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
 796                                         jiffies_to_usecs(jiffies - start));
 797
 798         return ret;
 799 }
 800 EXPORT_SYMBOL(congestion_wait);
 801
 802 /**
 803  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
 804  * @zone: A zone to check if it is heavily congested
 805  * @sync: SYNC or ASYNC IO
 806  * @timeout: timeout in jiffies
 807  *
 808  * In the event of a congested backing_dev (any backing_dev) and the given
 809  * @zone has experienced recent congestion, this waits for up to @timeout
 810  * jiffies for either a BDI to exit congestion of the given @sync queue
 811  * or a write to complete.
 812  *
 813  * In the absence of zone congestion, cond_resched() is called to yield
 814  * the processor if necessary but otherwise does not sleep.
 815  *
 816  * The return value is 0 if the sleep is for the full timeout. Otherwise,
 817  * it is the number of jiffies that were still remaining when the function
 818  * returned. return_value == timeout implies the function did not sleep.
 819  */
 820 long wait_iff_congested(struct zone *zone, int sync, long timeout)
 821 {
 822         long ret;
 823         unsigned long start = jiffies;
 824         DEFINE_WAIT(wait);
 825         wait_queue_head_t *wqh = &congestion_wqh[sync];
 826
 827         /*
 828          * If there is no congestion, or heavy congestion is not being
 829          * encountered in the current zone, yield if necessary instead
 830          * of sleeping on the congestion queue
 831          */
 832         if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
 833                         !zone_is_reclaim_congested(zone)) {
 834                 cond_resched();
 835
 836                 /* In case we scheduled, work out time remaining */
 837                 ret = timeout - (jiffies - start);
 838                 if (ret < 0)
 839                         ret = 0;
 840
 841                 goto out;
 842         }
 843
 844         /* Sleep until uncongested or a write happens */
 845         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 846         ret = io_schedule_timeout(timeout);
 847         finish_wait(wqh, &wait);
 848
 849 out:
 850         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
 851                                         jiffies_to_usecs(jiffies - start));
 852
 853         return ret;
 854 }
 855 EXPORT_SYMBOL(wait_iff_congested);