linux/fs/fs-writeback.c
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   1/*
   2 * fs/fs-writeback.c
   3 *
   4 * Copyright (C) 2002, Linus Torvalds.
   5 *
   6 * Contains all the functions related to writing back and waiting
   7 * upon dirty inodes against superblocks, and writing back dirty
   8 * pages against inodes.  ie: data writeback.  Writeout of the
   9 * inode itself is not handled here.
  10 *
  11 * 10Apr2002    Andrew Morton
  12 *              Split out of fs/inode.c
  13 *              Additions for address_space-based writeback
  14 */
  15
  16#include <linux/kernel.h>
  17#include <linux/export.h>
  18#include <linux/spinlock.h>
  19#include <linux/slab.h>
  20#include <linux/sched.h>
  21#include <linux/fs.h>
  22#include <linux/mm.h>
  23#include <linux/pagemap.h>
  24#include <linux/kthread.h>
  25#include <linux/writeback.h>
  26#include <linux/blkdev.h>
  27#include <linux/backing-dev.h>
  28#include <linux/tracepoint.h>
  29#include <linux/device.h>
  30#include "internal.h"
  31
  32/*
  33 * 4MB minimal write chunk size
  34 */
  35#define MIN_WRITEBACK_PAGES     (4096UL >> (PAGE_CACHE_SHIFT - 10))
  36
  37/*
  38 * Passed into wb_writeback(), essentially a subset of writeback_control
  39 */
  40struct wb_writeback_work {
  41        long nr_pages;
  42        struct super_block *sb;
  43        /*
  44         * Write only inodes dirtied before this time. Don't forget to set
  45         * older_than_this_is_set when you set this.
  46         */
  47        unsigned long older_than_this;
  48        enum writeback_sync_modes sync_mode;
  49        unsigned int tagged_writepages:1;
  50        unsigned int for_kupdate:1;
  51        unsigned int range_cyclic:1;
  52        unsigned int for_background:1;
  53        unsigned int for_sync:1;        /* sync(2) WB_SYNC_ALL writeback */
  54        unsigned int older_than_this_is_set:1;
  55        enum wb_reason reason;          /* why was writeback initiated? */
  56
  57        struct list_head list;          /* pending work list */
  58        struct completion *done;        /* set if the caller waits */
  59};
  60
  61/**
  62 * writeback_in_progress - determine whether there is writeback in progress
  63 * @bdi: the device's backing_dev_info structure.
  64 *
  65 * Determine whether there is writeback waiting to be handled against a
  66 * backing device.
  67 */
  68int writeback_in_progress(struct backing_dev_info *bdi)
  69{
  70        return test_bit(BDI_writeback_running, &bdi->state);
  71}
  72EXPORT_SYMBOL(writeback_in_progress);
  73
  74static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
  75{
  76        struct super_block *sb = inode->i_sb;
  77
  78        if (sb_is_blkdev_sb(sb))
  79                return inode->i_mapping->backing_dev_info;
  80
  81        return sb->s_bdi;
  82}
  83
  84static inline struct inode *wb_inode(struct list_head *head)
  85{
  86        return list_entry(head, struct inode, i_wb_list);
  87}
  88
  89/*
  90 * Include the creation of the trace points after defining the
  91 * wb_writeback_work structure and inline functions so that the definition
  92 * remains local to this file.
  93 */
  94#define CREATE_TRACE_POINTS
  95#include <trace/events/writeback.h>
  96
  97static void bdi_queue_work(struct backing_dev_info *bdi,
  98                           struct wb_writeback_work *work)
  99{
 100        trace_writeback_queue(bdi, work);
 101
 102        spin_lock_bh(&bdi->wb_lock);
 103        list_add_tail(&work->list, &bdi->work_list);
 104        spin_unlock_bh(&bdi->wb_lock);
 105
 106        mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
 107}
 108
 109static void
 110__bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
 111                      bool range_cyclic, enum wb_reason reason)
 112{
 113        struct wb_writeback_work *work;
 114
 115        /*
 116         * This is WB_SYNC_NONE writeback, so if allocation fails just
 117         * wakeup the thread for old dirty data writeback
 118         */
 119        work = kzalloc(sizeof(*work), GFP_ATOMIC);
 120        if (!work) {
 121                trace_writeback_nowork(bdi);
 122                mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
 123                return;
 124        }
 125
 126        work->sync_mode = WB_SYNC_NONE;
 127        work->nr_pages  = nr_pages;
 128        work->range_cyclic = range_cyclic;
 129        work->reason    = reason;
 130
 131        bdi_queue_work(bdi, work);
 132}
 133
 134/**
 135 * bdi_start_writeback - start writeback
 136 * @bdi: the backing device to write from
 137 * @nr_pages: the number of pages to write
 138 * @reason: reason why some writeback work was initiated
 139 *
 140 * Description:
 141 *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
 142 *   started when this function returns, we make no guarantees on
 143 *   completion. Caller need not hold sb s_umount semaphore.
 144 *
 145 */
 146void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
 147                        enum wb_reason reason)
 148{
 149        __bdi_start_writeback(bdi, nr_pages, true, reason);
 150}
 151
 152/**
 153 * bdi_start_background_writeback - start background writeback
 154 * @bdi: the backing device to write from
 155 *
 156 * Description:
 157 *   This makes sure WB_SYNC_NONE background writeback happens. When
 158 *   this function returns, it is only guaranteed that for given BDI
 159 *   some IO is happening if we are over background dirty threshold.
 160 *   Caller need not hold sb s_umount semaphore.
 161 */
 162void bdi_start_background_writeback(struct backing_dev_info *bdi)
 163{
 164        /*
 165         * We just wake up the flusher thread. It will perform background
 166         * writeback as soon as there is no other work to do.
 167         */
 168        trace_writeback_wake_background(bdi);
 169        mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
 170}
 171
 172/*
 173 * Remove the inode from the writeback list it is on.
 174 */
 175void inode_wb_list_del(struct inode *inode)
 176{
 177        struct backing_dev_info *bdi = inode_to_bdi(inode);
 178
 179        spin_lock(&bdi->wb.list_lock);
 180        list_del_init(&inode->i_wb_list);
 181        spin_unlock(&bdi->wb.list_lock);
 182}
 183
 184/*
 185 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
 186 * furthest end of its superblock's dirty-inode list.
 187 *
 188 * Before stamping the inode's ->dirtied_when, we check to see whether it is
 189 * already the most-recently-dirtied inode on the b_dirty list.  If that is
 190 * the case then the inode must have been redirtied while it was being written
 191 * out and we don't reset its dirtied_when.
 192 */
 193static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
 194{
 195        assert_spin_locked(&wb->list_lock);
 196        if (!list_empty(&wb->b_dirty)) {
 197                struct inode *tail;
 198
 199                tail = wb_inode(wb->b_dirty.next);
 200                if (time_before(inode->dirtied_when, tail->dirtied_when))
 201                        inode->dirtied_when = jiffies;
 202        }
 203        list_move(&inode->i_wb_list, &wb->b_dirty);
 204}
 205
 206/*
 207 * requeue inode for re-scanning after bdi->b_io list is exhausted.
 208 */
 209static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
 210{
 211        assert_spin_locked(&wb->list_lock);
 212        list_move(&inode->i_wb_list, &wb->b_more_io);
 213}
 214
 215static void inode_sync_complete(struct inode *inode)
 216{
 217        inode->i_state &= ~I_SYNC;
 218        /* If inode is clean an unused, put it into LRU now... */
 219        inode_add_lru(inode);
 220        /* Waiters must see I_SYNC cleared before being woken up */
 221        smp_mb();
 222        wake_up_bit(&inode->i_state, __I_SYNC);
 223}
 224
 225static bool inode_dirtied_after(struct inode *inode, unsigned long t)
 226{
 227        bool ret = time_after(inode->dirtied_when, t);
 228#ifndef CONFIG_64BIT
 229        /*
 230         * For inodes being constantly redirtied, dirtied_when can get stuck.
 231         * It _appears_ to be in the future, but is actually in distant past.
 232         * This test is necessary to prevent such wrapped-around relative times
 233         * from permanently stopping the whole bdi writeback.
 234         */
 235        ret = ret && time_before_eq(inode->dirtied_when, jiffies);
 236#endif
 237        return ret;
 238}
 239
 240/*
 241 * Move expired (dirtied before work->older_than_this) dirty inodes from
 242 * @delaying_queue to @dispatch_queue.
 243 */
 244static int move_expired_inodes(struct list_head *delaying_queue,
 245                               struct list_head *dispatch_queue,
 246                               struct wb_writeback_work *work)
 247{
 248        LIST_HEAD(tmp);
 249        struct list_head *pos, *node;
 250        struct super_block *sb = NULL;
 251        struct inode *inode;
 252        int do_sb_sort = 0;
 253        int moved = 0;
 254
 255        WARN_ON_ONCE(!work->older_than_this_is_set);
 256        while (!list_empty(delaying_queue)) {
 257                inode = wb_inode(delaying_queue->prev);
 258                if (inode_dirtied_after(inode, work->older_than_this))
 259                        break;
 260                list_move(&inode->i_wb_list, &tmp);
 261                moved++;
 262                if (sb_is_blkdev_sb(inode->i_sb))
 263                        continue;
 264                if (sb && sb != inode->i_sb)
 265                        do_sb_sort = 1;
 266                sb = inode->i_sb;
 267        }
 268
 269        /* just one sb in list, splice to dispatch_queue and we're done */
 270        if (!do_sb_sort) {
 271                list_splice(&tmp, dispatch_queue);
 272                goto out;
 273        }
 274
 275        /* Move inodes from one superblock together */
 276        while (!list_empty(&tmp)) {
 277                sb = wb_inode(tmp.prev)->i_sb;
 278                list_for_each_prev_safe(pos, node, &tmp) {
 279                        inode = wb_inode(pos);
 280                        if (inode->i_sb == sb)
 281                                list_move(&inode->i_wb_list, dispatch_queue);
 282                }
 283        }
 284out:
 285        return moved;
 286}
 287
 288/*
 289 * Queue all expired dirty inodes for io, eldest first.
 290 * Before
 291 *         newly dirtied     b_dirty    b_io    b_more_io
 292 *         =============>    gf         edc     BA
 293 * After
 294 *         newly dirtied     b_dirty    b_io    b_more_io
 295 *         =============>    g          fBAedc
 296 *                                           |
 297 *                                           +--> dequeue for IO
 298 */
 299static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
 300{
 301        int moved;
 302        assert_spin_locked(&wb->list_lock);
 303        list_splice_init(&wb->b_more_io, &wb->b_io);
 304        moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
 305        trace_writeback_queue_io(wb, work, moved);
 306}
 307
 308static int write_inode(struct inode *inode, struct writeback_control *wbc)
 309{
 310        int ret;
 311
 312        if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
 313                trace_writeback_write_inode_start(inode, wbc);
 314                ret = inode->i_sb->s_op->write_inode(inode, wbc);
 315                trace_writeback_write_inode(inode, wbc);
 316                return ret;
 317        }
 318        return 0;
 319}
 320
 321/*
 322 * Wait for writeback on an inode to complete. Called with i_lock held.
 323 * Caller must make sure inode cannot go away when we drop i_lock.
 324 */
 325static void __inode_wait_for_writeback(struct inode *inode)
 326        __releases(inode->i_lock)
 327        __acquires(inode->i_lock)
 328{
 329        DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
 330        wait_queue_head_t *wqh;
 331
 332        wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 333        while (inode->i_state & I_SYNC) {
 334                spin_unlock(&inode->i_lock);
 335                __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
 336                spin_lock(&inode->i_lock);
 337        }
 338}
 339
 340/*
 341 * Wait for writeback on an inode to complete. Caller must have inode pinned.
 342 */
 343void inode_wait_for_writeback(struct inode *inode)
 344{
 345        spin_lock(&inode->i_lock);
 346        __inode_wait_for_writeback(inode);
 347        spin_unlock(&inode->i_lock);
 348}
 349
 350/*
 351 * Sleep until I_SYNC is cleared. This function must be called with i_lock
 352 * held and drops it. It is aimed for callers not holding any inode reference
 353 * so once i_lock is dropped, inode can go away.
 354 */
 355static void inode_sleep_on_writeback(struct inode *inode)
 356        __releases(inode->i_lock)
 357{
 358        DEFINE_WAIT(wait);
 359        wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 360        int sleep;
 361
 362        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 363        sleep = inode->i_state & I_SYNC;
 364        spin_unlock(&inode->i_lock);
 365        if (sleep)
 366                schedule();
 367        finish_wait(wqh, &wait);
 368}
 369
 370/*
 371 * Find proper writeback list for the inode depending on its current state and
 372 * possibly also change of its state while we were doing writeback.  Here we
 373 * handle things such as livelock prevention or fairness of writeback among
 374 * inodes. This function can be called only by flusher thread - noone else
 375 * processes all inodes in writeback lists and requeueing inodes behind flusher
 376 * thread's back can have unexpected consequences.
 377 */
 378static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
 379                          struct writeback_control *wbc)
 380{
 381        if (inode->i_state & I_FREEING)
 382                return;
 383
 384        /*
 385         * Sync livelock prevention. Each inode is tagged and synced in one
 386         * shot. If still dirty, it will be redirty_tail()'ed below.  Update
 387         * the dirty time to prevent enqueue and sync it again.
 388         */
 389        if ((inode->i_state & I_DIRTY) &&
 390            (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
 391                inode->dirtied_when = jiffies;
 392
 393        if (wbc->pages_skipped) {
 394                /*
 395                 * writeback is not making progress due to locked
 396                 * buffers. Skip this inode for now.
 397                 */
 398                redirty_tail(inode, wb);
 399                return;
 400        }
 401
 402        if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
 403                /*
 404                 * We didn't write back all the pages.  nfs_writepages()
 405                 * sometimes bales out without doing anything.
 406                 */
 407                if (wbc->nr_to_write <= 0) {
 408                        /* Slice used up. Queue for next turn. */
 409                        requeue_io(inode, wb);
 410                } else {
 411                        /*
 412                         * Writeback blocked by something other than
 413                         * congestion. Delay the inode for some time to
 414                         * avoid spinning on the CPU (100% iowait)
 415                         * retrying writeback of the dirty page/inode
 416                         * that cannot be performed immediately.
 417                         */
 418                        redirty_tail(inode, wb);
 419                }
 420        } else if (inode->i_state & I_DIRTY) {
 421                /*
 422                 * Filesystems can dirty the inode during writeback operations,
 423                 * such as delayed allocation during submission or metadata
 424                 * updates after data IO completion.
 425                 */
 426                redirty_tail(inode, wb);
 427        } else {
 428                /* The inode is clean. Remove from writeback lists. */
 429                list_del_init(&inode->i_wb_list);
 430        }
 431}
 432
 433/*
 434 * Write out an inode and its dirty pages. Do not update the writeback list
 435 * linkage. That is left to the caller. The caller is also responsible for
 436 * setting I_SYNC flag and calling inode_sync_complete() to clear it.
 437 */
 438static int
 439__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 440{
 441        struct address_space *mapping = inode->i_mapping;
 442        long nr_to_write = wbc->nr_to_write;
 443        unsigned dirty;
 444        int ret;
 445
 446        WARN_ON(!(inode->i_state & I_SYNC));
 447
 448        trace_writeback_single_inode_start(inode, wbc, nr_to_write);
 449
 450        ret = do_writepages(mapping, wbc);
 451
 452        /*
 453         * Make sure to wait on the data before writing out the metadata.
 454         * This is important for filesystems that modify metadata on data
 455         * I/O completion. We don't do it for sync(2) writeback because it has a
 456         * separate, external IO completion path and ->sync_fs for guaranteeing
 457         * inode metadata is written back correctly.
 458         */
 459        if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
 460                int err = filemap_fdatawait(mapping);
 461                if (ret == 0)
 462                        ret = err;
 463        }
 464
 465        /*
 466         * Some filesystems may redirty the inode during the writeback
 467         * due to delalloc, clear dirty metadata flags right before
 468         * write_inode()
 469         */
 470        spin_lock(&inode->i_lock);
 471        /* Clear I_DIRTY_PAGES if we've written out all dirty pages */
 472        if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
 473                inode->i_state &= ~I_DIRTY_PAGES;
 474        dirty = inode->i_state & I_DIRTY;
 475        inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
 476        spin_unlock(&inode->i_lock);
 477        /* Don't write the inode if only I_DIRTY_PAGES was set */
 478        if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
 479                int err = write_inode(inode, wbc);
 480                if (ret == 0)
 481                        ret = err;
 482        }
 483        trace_writeback_single_inode(inode, wbc, nr_to_write);
 484        return ret;
 485}
 486
 487/*
 488 * Write out an inode's dirty pages. Either the caller has an active reference
 489 * on the inode or the inode has I_WILL_FREE set.
 490 *
 491 * This function is designed to be called for writing back one inode which
 492 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
 493 * and does more profound writeback list handling in writeback_sb_inodes().
 494 */
 495static int
 496writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
 497                       struct writeback_control *wbc)
 498{
 499        int ret = 0;
 500
 501        spin_lock(&inode->i_lock);
 502        if (!atomic_read(&inode->i_count))
 503                WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
 504        else
 505                WARN_ON(inode->i_state & I_WILL_FREE);
 506
 507        if (inode->i_state & I_SYNC) {
 508                if (wbc->sync_mode != WB_SYNC_ALL)
 509                        goto out;
 510                /*
 511                 * It's a data-integrity sync. We must wait. Since callers hold
 512                 * inode reference or inode has I_WILL_FREE set, it cannot go
 513                 * away under us.
 514                 */
 515                __inode_wait_for_writeback(inode);
 516        }
 517        WARN_ON(inode->i_state & I_SYNC);
 518        /*
 519         * Skip inode if it is clean and we have no outstanding writeback in
 520         * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
 521         * function since flusher thread may be doing for example sync in
 522         * parallel and if we move the inode, it could get skipped. So here we
 523         * make sure inode is on some writeback list and leave it there unless
 524         * we have completely cleaned the inode.
 525         */
 526        if (!(inode->i_state & I_DIRTY) &&
 527            (wbc->sync_mode != WB_SYNC_ALL ||
 528             !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
 529                goto out;
 530        inode->i_state |= I_SYNC;
 531        spin_unlock(&inode->i_lock);
 532
 533        ret = __writeback_single_inode(inode, wbc);
 534
 535        spin_lock(&wb->list_lock);
 536        spin_lock(&inode->i_lock);
 537        /*
 538         * If inode is clean, remove it from writeback lists. Otherwise don't
 539         * touch it. See comment above for explanation.
 540         */
 541        if (!(inode->i_state & I_DIRTY))
 542                list_del_init(&inode->i_wb_list);
 543        spin_unlock(&wb->list_lock);
 544        inode_sync_complete(inode);
 545out:
 546        spin_unlock(&inode->i_lock);
 547        return ret;
 548}
 549
 550static long writeback_chunk_size(struct backing_dev_info *bdi,
 551                                 struct wb_writeback_work *work)
 552{
 553        long pages;
 554
 555        /*
 556         * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
 557         * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
 558         * here avoids calling into writeback_inodes_wb() more than once.
 559         *
 560         * The intended call sequence for WB_SYNC_ALL writeback is:
 561         *
 562         *      wb_writeback()
 563         *          writeback_sb_inodes()       <== called only once
 564         *              write_cache_pages()     <== called once for each inode
 565         *                   (quickly) tag currently dirty pages
 566         *                   (maybe slowly) sync all tagged pages
 567         */
 568        if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
 569                pages = LONG_MAX;
 570        else {
 571                pages = min(bdi->avg_write_bandwidth / 2,
 572                            global_dirty_limit / DIRTY_SCOPE);
 573                pages = min(pages, work->nr_pages);
 574                pages = round_down(pages + MIN_WRITEBACK_PAGES,
 575                                   MIN_WRITEBACK_PAGES);
 576        }
 577
 578        return pages;
 579}
 580
 581/*
 582 * Write a portion of b_io inodes which belong to @sb.
 583 *
 584 * Return the number of pages and/or inodes written.
 585 */
 586static long writeback_sb_inodes(struct super_block *sb,
 587                                struct bdi_writeback *wb,
 588                                struct wb_writeback_work *work)
 589{
 590        struct writeback_control wbc = {
 591                .sync_mode              = work->sync_mode,
 592                .tagged_writepages      = work->tagged_writepages,
 593                .for_kupdate            = work->for_kupdate,
 594                .for_background         = work->for_background,
 595                .for_sync               = work->for_sync,
 596                .range_cyclic           = work->range_cyclic,
 597                .range_start            = 0,
 598                .range_end              = LLONG_MAX,
 599        };
 600        unsigned long start_time = jiffies;
 601        long write_chunk;
 602        long wrote = 0;  /* count both pages and inodes */
 603
 604        while (!list_empty(&wb->b_io)) {
 605                struct inode *inode = wb_inode(wb->b_io.prev);
 606
 607                if (inode->i_sb != sb) {
 608                        if (work->sb) {
 609                                /*
 610                                 * We only want to write back data for this
 611                                 * superblock, move all inodes not belonging
 612                                 * to it back onto the dirty list.
 613                                 */
 614                                redirty_tail(inode, wb);
 615                                continue;
 616                        }
 617
 618                        /*
 619                         * The inode belongs to a different superblock.
 620                         * Bounce back to the caller to unpin this and
 621                         * pin the next superblock.
 622                         */
 623                        break;
 624                }
 625
 626                /*
 627                 * Don't bother with new inodes or inodes being freed, first
 628                 * kind does not need periodic writeout yet, and for the latter
 629                 * kind writeout is handled by the freer.
 630                 */
 631                spin_lock(&inode->i_lock);
 632                if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
 633                        spin_unlock(&inode->i_lock);
 634                        redirty_tail(inode, wb);
 635                        continue;
 636                }
 637                if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
 638                        /*
 639                         * If this inode is locked for writeback and we are not
 640                         * doing writeback-for-data-integrity, move it to
 641                         * b_more_io so that writeback can proceed with the
 642                         * other inodes on s_io.
 643                         *
 644                         * We'll have another go at writing back this inode
 645                         * when we completed a full scan of b_io.
 646                         */
 647                        spin_unlock(&inode->i_lock);
 648                        requeue_io(inode, wb);
 649                        trace_writeback_sb_inodes_requeue(inode);
 650                        continue;
 651                }
 652                spin_unlock(&wb->list_lock);
 653
 654                /*
 655                 * We already requeued the inode if it had I_SYNC set and we
 656                 * are doing WB_SYNC_NONE writeback. So this catches only the
 657                 * WB_SYNC_ALL case.
 658                 */
 659                if (inode->i_state & I_SYNC) {
 660                        /* Wait for I_SYNC. This function drops i_lock... */
 661                        inode_sleep_on_writeback(inode);
 662                        /* Inode may be gone, start again */
 663                        spin_lock(&wb->list_lock);
 664                        continue;
 665                }
 666                inode->i_state |= I_SYNC;
 667                spin_unlock(&inode->i_lock);
 668
 669                write_chunk = writeback_chunk_size(wb->bdi, work);
 670                wbc.nr_to_write = write_chunk;
 671                wbc.pages_skipped = 0;
 672
 673                /*
 674                 * We use I_SYNC to pin the inode in memory. While it is set
 675                 * evict_inode() will wait so the inode cannot be freed.
 676                 */
 677                __writeback_single_inode(inode, &wbc);
 678
 679                work->nr_pages -= write_chunk - wbc.nr_to_write;
 680                wrote += write_chunk - wbc.nr_to_write;
 681                spin_lock(&wb->list_lock);
 682                spin_lock(&inode->i_lock);
 683                if (!(inode->i_state & I_DIRTY))
 684                        wrote++;
 685                requeue_inode(inode, wb, &wbc);
 686                inode_sync_complete(inode);
 687                spin_unlock(&inode->i_lock);
 688                cond_resched_lock(&wb->list_lock);
 689                /*
 690                 * bail out to wb_writeback() often enough to check
 691                 * background threshold and other termination conditions.
 692                 */
 693                if (wrote) {
 694                        if (time_is_before_jiffies(start_time + HZ / 10UL))
 695                                break;
 696                        if (work->nr_pages <= 0)
 697                                break;
 698                }
 699        }
 700        return wrote;
 701}
 702
 703static long __writeback_inodes_wb(struct bdi_writeback *wb,
 704                                  struct wb_writeback_work *work)
 705{
 706        unsigned long start_time = jiffies;
 707        long wrote = 0;
 708
 709        while (!list_empty(&wb->b_io)) {
 710                struct inode *inode = wb_inode(wb->b_io.prev);
 711                struct super_block *sb = inode->i_sb;
 712
 713                if (!grab_super_passive(sb)) {
 714                        /*
 715                         * grab_super_passive() may fail consistently due to
 716                         * s_umount being grabbed by someone else. Don't use
 717                         * requeue_io() to avoid busy retrying the inode/sb.
 718                         */
 719                        redirty_tail(inode, wb);
 720                        continue;
 721                }
 722                wrote += writeback_sb_inodes(sb, wb, work);
 723                drop_super(sb);
 724
 725                /* refer to the same tests at the end of writeback_sb_inodes */
 726                if (wrote) {
 727                        if (time_is_before_jiffies(start_time + HZ / 10UL))
 728                                break;
 729                        if (work->nr_pages <= 0)
 730                                break;
 731                }
 732        }
 733        /* Leave any unwritten inodes on b_io */
 734        return wrote;
 735}
 736
 737static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
 738                                enum wb_reason reason)
 739{
 740        struct wb_writeback_work work = {
 741                .nr_pages       = nr_pages,
 742                .sync_mode      = WB_SYNC_NONE,
 743                .range_cyclic   = 1,
 744                .reason         = reason,
 745                .older_than_this = jiffies,
 746                .older_than_this_is_set = 1,
 747        };
 748
 749        spin_lock(&wb->list_lock);
 750        if (list_empty(&wb->b_io))
 751                queue_io(wb, &work);
 752        __writeback_inodes_wb(wb, &work);
 753        spin_unlock(&wb->list_lock);
 754
 755        return nr_pages - work.nr_pages;
 756}
 757
 758static bool over_bground_thresh(struct backing_dev_info *bdi)
 759{
 760        unsigned long background_thresh, dirty_thresh;
 761
 762        global_dirty_limits(&background_thresh, &dirty_thresh);
 763
 764        if (global_page_state(NR_FILE_DIRTY) +
 765            global_page_state(NR_UNSTABLE_NFS) > background_thresh)
 766                return true;
 767
 768        if (bdi_stat(bdi, BDI_RECLAIMABLE) >
 769                                bdi_dirty_limit(bdi, background_thresh))
 770                return true;
 771
 772        return false;
 773}
 774
 775/*
 776 * Called under wb->list_lock. If there are multiple wb per bdi,
 777 * only the flusher working on the first wb should do it.
 778 */
 779static void wb_update_bandwidth(struct bdi_writeback *wb,
 780                                unsigned long start_time)
 781{
 782        __bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
 783}
 784
 785/*
 786 * Explicit flushing or periodic writeback of "old" data.
 787 *
 788 * Define "old": the first time one of an inode's pages is dirtied, we mark the
 789 * dirtying-time in the inode's address_space.  So this periodic writeback code
 790 * just walks the superblock inode list, writing back any inodes which are
 791 * older than a specific point in time.
 792 *
 793 * Try to run once per dirty_writeback_interval.  But if a writeback event
 794 * takes longer than a dirty_writeback_interval interval, then leave a
 795 * one-second gap.
 796 *
 797 * older_than_this takes precedence over nr_to_write.  So we'll only write back
 798 * all dirty pages if they are all attached to "old" mappings.
 799 */
 800static long wb_writeback(struct bdi_writeback *wb,
 801                         struct wb_writeback_work *work)
 802{
 803        unsigned long wb_start = jiffies;
 804        long nr_pages = work->nr_pages;
 805        struct inode *inode;
 806        long progress;
 807
 808        if (!work->older_than_this_is_set) {
 809                work->older_than_this = jiffies;
 810                work->older_than_this_is_set = 1;
 811        }
 812
 813        spin_lock(&wb->list_lock);
 814        for (;;) {
 815                /*
 816                 * Stop writeback when nr_pages has been consumed
 817                 */
 818                if (work->nr_pages <= 0)
 819                        break;
 820
 821                /*
 822                 * Background writeout and kupdate-style writeback may
 823                 * run forever. Stop them if there is other work to do
 824                 * so that e.g. sync can proceed. They'll be restarted
 825                 * after the other works are all done.
 826                 */
 827                if ((work->for_background || work->for_kupdate) &&
 828                    !list_empty(&wb->bdi->work_list))
 829                        break;
 830
 831                /*
 832                 * For background writeout, stop when we are below the
 833                 * background dirty threshold
 834                 */
 835                if (work->for_background && !over_bground_thresh(wb->bdi))
 836                        break;
 837
 838                /*
 839                 * Kupdate and background works are special and we want to
 840                 * include all inodes that need writing. Livelock avoidance is
 841                 * handled by these works yielding to any other work so we are
 842                 * safe.
 843                 */
 844                if (work->for_kupdate) {
 845                        work->older_than_this = jiffies -
 846                                msecs_to_jiffies(dirty_expire_interval * 10);
 847                } else if (work->for_background)
 848                        work->older_than_this = jiffies;
 849
 850                trace_writeback_start(wb->bdi, work);
 851                if (list_empty(&wb->b_io))
 852                        queue_io(wb, work);
 853                if (work->sb)
 854                        progress = writeback_sb_inodes(work->sb, wb, work);
 855                else
 856                        progress = __writeback_inodes_wb(wb, work);
 857                trace_writeback_written(wb->bdi, work);
 858
 859                wb_update_bandwidth(wb, wb_start);
 860
 861                /*
 862                 * Did we write something? Try for more
 863                 *
 864                 * Dirty inodes are moved to b_io for writeback in batches.
 865                 * The completion of the current batch does not necessarily
 866                 * mean the overall work is done. So we keep looping as long
 867                 * as made some progress on cleaning pages or inodes.
 868                 */
 869                if (progress)
 870                        continue;
 871                /*
 872                 * No more inodes for IO, bail
 873                 */
 874                if (list_empty(&wb->b_more_io))
 875                        break;
 876                /*
 877                 * Nothing written. Wait for some inode to
 878                 * become available for writeback. Otherwise
 879                 * we'll just busyloop.
 880                 */
 881                if (!list_empty(&wb->b_more_io))  {
 882                        trace_writeback_wait(wb->bdi, work);
 883                        inode = wb_inode(wb->b_more_io.prev);
 884                        spin_lock(&inode->i_lock);
 885                        spin_unlock(&wb->list_lock);
 886                        /* This function drops i_lock... */
 887                        inode_sleep_on_writeback(inode);
 888                        spin_lock(&wb->list_lock);
 889                }
 890        }
 891        spin_unlock(&wb->list_lock);
 892
 893        return nr_pages - work->nr_pages;
 894}
 895
 896/*
 897 * Return the next wb_writeback_work struct that hasn't been processed yet.
 898 */
 899static struct wb_writeback_work *
 900get_next_work_item(struct backing_dev_info *bdi)
 901{
 902        struct wb_writeback_work *work = NULL;
 903
 904        spin_lock_bh(&bdi->wb_lock);
 905        if (!list_empty(&bdi->work_list)) {
 906                work = list_entry(bdi->work_list.next,
 907                                  struct wb_writeback_work, list);
 908                list_del_init(&work->list);
 909        }
 910        spin_unlock_bh(&bdi->wb_lock);
 911        return work;
 912}
 913
 914/*
 915 * Add in the number of potentially dirty inodes, because each inode
 916 * write can dirty pagecache in the underlying blockdev.
 917 */
 918static unsigned long get_nr_dirty_pages(void)
 919{
 920        return global_page_state(NR_FILE_DIRTY) +
 921                global_page_state(NR_UNSTABLE_NFS) +
 922                get_nr_dirty_inodes();
 923}
 924
 925static long wb_check_background_flush(struct bdi_writeback *wb)
 926{
 927        if (over_bground_thresh(wb->bdi)) {
 928
 929                struct wb_writeback_work work = {
 930                        .nr_pages       = LONG_MAX,
 931                        .sync_mode      = WB_SYNC_NONE,
 932                        .for_background = 1,
 933                        .range_cyclic   = 1,
 934                        .reason         = WB_REASON_BACKGROUND,
 935                };
 936
 937                return wb_writeback(wb, &work);
 938        }
 939
 940        return 0;
 941}
 942
 943static long wb_check_old_data_flush(struct bdi_writeback *wb)
 944{
 945        unsigned long expired;
 946        long nr_pages;
 947
 948        /*
 949         * When set to zero, disable periodic writeback
 950         */
 951        if (!dirty_writeback_interval)
 952                return 0;
 953
 954        expired = wb->last_old_flush +
 955                        msecs_to_jiffies(dirty_writeback_interval * 10);
 956        if (time_before(jiffies, expired))
 957                return 0;
 958
 959        wb->last_old_flush = jiffies;
 960        nr_pages = get_nr_dirty_pages();
 961
 962        if (nr_pages) {
 963                struct wb_writeback_work work = {
 964                        .nr_pages       = nr_pages,
 965                        .sync_mode      = WB_SYNC_NONE,
 966                        .for_kupdate    = 1,
 967                        .range_cyclic   = 1,
 968                        .reason         = WB_REASON_PERIODIC,
 969                };
 970
 971                return wb_writeback(wb, &work);
 972        }
 973
 974        return 0;
 975}
 976
 977/*
 978 * Retrieve work items and do the writeback they describe
 979 */
 980static long wb_do_writeback(struct bdi_writeback *wb)
 981{
 982        struct backing_dev_info *bdi = wb->bdi;
 983        struct wb_writeback_work *work;
 984        long wrote = 0;
 985
 986        set_bit(BDI_writeback_running, &wb->bdi->state);
 987        while ((work = get_next_work_item(bdi)) != NULL) {
 988
 989                trace_writeback_exec(bdi, work);
 990
 991                wrote += wb_writeback(wb, work);
 992
 993                /*
 994                 * Notify the caller of completion if this is a synchronous
 995                 * work item, otherwise just free it.
 996                 */
 997                if (work->done)
 998                        complete(work->done);
 999                else
1000                        kfree(work);
1001        }
1002
1003        /*
1004         * Check for periodic writeback, kupdated() style
1005         */
1006        wrote += wb_check_old_data_flush(wb);
1007        wrote += wb_check_background_flush(wb);
1008        clear_bit(BDI_writeback_running, &wb->bdi->state);
1009
1010        return wrote;
1011}
1012
1013/*
1014 * Handle writeback of dirty data for the device backed by this bdi. Also
1015 * reschedules periodically and does kupdated style flushing.
1016 */
1017void bdi_writeback_workfn(struct work_struct *work)
1018{
1019        struct bdi_writeback *wb = container_of(to_delayed_work(work),
1020                                                struct bdi_writeback, dwork);
1021        struct backing_dev_info *bdi = wb->bdi;
1022        long pages_written;
1023
1024        set_worker_desc("flush-%s", dev_name(bdi->dev));
1025        current->flags |= PF_SWAPWRITE;
1026
1027        if (likely(!current_is_workqueue_rescuer() ||
1028                   list_empty(&bdi->bdi_list))) {
1029                /*
1030                 * The normal path.  Keep writing back @bdi until its
1031                 * work_list is empty.  Note that this path is also taken
1032                 * if @bdi is shutting down even when we're running off the
1033                 * rescuer as work_list needs to be drained.
1034                 */
1035                do {
1036                        pages_written = wb_do_writeback(wb);
1037                        trace_writeback_pages_written(pages_written);
1038                } while (!list_empty(&bdi->work_list));
1039        } else {
1040                /*
1041                 * bdi_wq can't get enough workers and we're running off
1042                 * the emergency worker.  Don't hog it.  Hopefully, 1024 is
1043                 * enough for efficient IO.
1044                 */
1045                pages_written = writeback_inodes_wb(&bdi->wb, 1024,
1046                                                    WB_REASON_FORKER_THREAD);
1047                trace_writeback_pages_written(pages_written);
1048        }
1049
1050        if (!list_empty(&bdi->work_list) ||
1051            (wb_has_dirty_io(wb) && dirty_writeback_interval))
1052                queue_delayed_work(bdi_wq, &wb->dwork,
1053                        msecs_to_jiffies(dirty_writeback_interval * 10));
1054
1055        current->flags &= ~PF_SWAPWRITE;
1056}
1057
1058/*
1059 * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
1060 * the whole world.
1061 */
1062void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
1063{
1064        struct backing_dev_info *bdi;
1065
1066        if (!nr_pages)
1067                nr_pages = get_nr_dirty_pages();
1068
1069        rcu_read_lock();
1070        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1071                if (!bdi_has_dirty_io(bdi))
1072                        continue;
1073                __bdi_start_writeback(bdi, nr_pages, false, reason);
1074        }
1075        rcu_read_unlock();
1076}
1077
1078static noinline void block_dump___mark_inode_dirty(struct inode *inode)
1079{
1080        if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
1081                struct dentry *dentry;
1082                const char *name = "?";
1083
1084                dentry = d_find_alias(inode);
1085                if (dentry) {
1086                        spin_lock(&dentry->d_lock);
1087                        name = (const char *) dentry->d_name.name;
1088                }
1089                printk(KERN_DEBUG
1090                       "%s(%d): dirtied inode %lu (%s) on %s\n",
1091                       current->comm, task_pid_nr(current), inode->i_ino,
1092                       name, inode->i_sb->s_id);
1093                if (dentry) {
1094                        spin_unlock(&dentry->d_lock);
1095                        dput(dentry);
1096                }
1097        }
1098}
1099
1100/**
1101 *      __mark_inode_dirty -    internal function
1102 *      @inode: inode to mark
1103 *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1104 *      Mark an inode as dirty. Callers should use mark_inode_dirty or
1105 *      mark_inode_dirty_sync.
1106 *
1107 * Put the inode on the super block's dirty list.
1108 *
1109 * CAREFUL! We mark it dirty unconditionally, but move it onto the
1110 * dirty list only if it is hashed or if it refers to a blockdev.
1111 * If it was not hashed, it will never be added to the dirty list
1112 * even if it is later hashed, as it will have been marked dirty already.
1113 *
1114 * In short, make sure you hash any inodes _before_ you start marking
1115 * them dirty.
1116 *
1117 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1118 * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
1119 * the kernel-internal blockdev inode represents the dirtying time of the
1120 * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
1121 * page->mapping->host, so the page-dirtying time is recorded in the internal
1122 * blockdev inode.
1123 */
1124void __mark_inode_dirty(struct inode *inode, int flags)
1125{
1126        struct super_block *sb = inode->i_sb;
1127        struct backing_dev_info *bdi = NULL;
1128
1129        /*
1130         * Don't do this for I_DIRTY_PAGES - that doesn't actually
1131         * dirty the inode itself
1132         */
1133        if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1134                trace_writeback_dirty_inode_start(inode, flags);
1135
1136                if (sb->s_op->dirty_inode)
1137                        sb->s_op->dirty_inode(inode, flags);
1138
1139                trace_writeback_dirty_inode(inode, flags);
1140        }
1141
1142        /*
1143         * make sure that changes are seen by all cpus before we test i_state
1144         * -- mikulas
1145         */
1146        smp_mb();
1147
1148        /* avoid the locking if we can */
1149        if ((inode->i_state & flags) == flags)
1150                return;
1151
1152        if (unlikely(block_dump))
1153                block_dump___mark_inode_dirty(inode);
1154
1155        spin_lock(&inode->i_lock);
1156        if ((inode->i_state & flags) != flags) {
1157                const int was_dirty = inode->i_state & I_DIRTY;
1158
1159                inode->i_state |= flags;
1160
1161                /*
1162                 * If the inode is being synced, just update its dirty state.
1163                 * The unlocker will place the inode on the appropriate
1164                 * superblock list, based upon its state.
1165                 */
1166                if (inode->i_state & I_SYNC)
1167                        goto out_unlock_inode;
1168
1169                /*
1170                 * Only add valid (hashed) inodes to the superblock's
1171                 * dirty list.  Add blockdev inodes as well.
1172                 */
1173                if (!S_ISBLK(inode->i_mode)) {
1174                        if (inode_unhashed(inode))
1175                                goto out_unlock_inode;
1176                }
1177                if (inode->i_state & I_FREEING)
1178                        goto out_unlock_inode;
1179
1180                /*
1181                 * If the inode was already on b_dirty/b_io/b_more_io, don't
1182                 * reposition it (that would break b_dirty time-ordering).
1183                 */
1184                if (!was_dirty) {
1185                        bool wakeup_bdi = false;
1186                        bdi = inode_to_bdi(inode);
1187
1188                        spin_unlock(&inode->i_lock);
1189                        spin_lock(&bdi->wb.list_lock);
1190                        if (bdi_cap_writeback_dirty(bdi)) {
1191                                WARN(!test_bit(BDI_registered, &bdi->state),
1192                                     "bdi-%s not registered\n", bdi->name);
1193
1194                                /*
1195                                 * If this is the first dirty inode for this
1196                                 * bdi, we have to wake-up the corresponding
1197                                 * bdi thread to make sure background
1198                                 * write-back happens later.
1199                                 */
1200                                if (!wb_has_dirty_io(&bdi->wb))
1201                                        wakeup_bdi = true;
1202                        }
1203
1204                        inode->dirtied_when = jiffies;
1205                        list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1206                        spin_unlock(&bdi->wb.list_lock);
1207
1208                        if (wakeup_bdi)
1209                                bdi_wakeup_thread_delayed(bdi);
1210                        return;
1211                }
1212        }
1213out_unlock_inode:
1214        spin_unlock(&inode->i_lock);
1215
1216}
1217EXPORT_SYMBOL(__mark_inode_dirty);
1218
1219static void wait_sb_inodes(struct super_block *sb)
1220{
1221        struct inode *inode, *old_inode = NULL;
1222
1223        /*
1224         * We need to be protected against the filesystem going from
1225         * r/o to r/w or vice versa.
1226         */
1227        WARN_ON(!rwsem_is_locked(&sb->s_umount));
1228
1229        spin_lock(&inode_sb_list_lock);
1230
1231        /*
1232         * Data integrity sync. Must wait for all pages under writeback,
1233         * because there may have been pages dirtied before our sync
1234         * call, but which had writeout started before we write it out.
1235         * In which case, the inode may not be on the dirty list, but
1236         * we still have to wait for that writeout.
1237         */
1238        list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1239                struct address_space *mapping = inode->i_mapping;
1240
1241                spin_lock(&inode->i_lock);
1242                if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
1243                    (mapping->nrpages == 0)) {
1244                        spin_unlock(&inode->i_lock);
1245                        continue;
1246                }
1247                __iget(inode);
1248                spin_unlock(&inode->i_lock);
1249                spin_unlock(&inode_sb_list_lock);
1250
1251                /*
1252                 * We hold a reference to 'inode' so it couldn't have been
1253                 * removed from s_inodes list while we dropped the
1254                 * inode_sb_list_lock.  We cannot iput the inode now as we can
1255                 * be holding the last reference and we cannot iput it under
1256                 * inode_sb_list_lock. So we keep the reference and iput it
1257                 * later.
1258                 */
1259                iput(old_inode);
1260                old_inode = inode;
1261
1262                filemap_fdatawait(mapping);
1263
1264                cond_resched();
1265
1266                spin_lock(&inode_sb_list_lock);
1267        }
1268        spin_unlock(&inode_sb_list_lock);
1269        iput(old_inode);
1270}
1271
1272/**
1273 * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
1274 * @sb: the superblock
1275 * @nr: the number of pages to write
1276 * @reason: reason why some writeback work initiated
1277 *
1278 * Start writeback on some inodes on this super_block. No guarantees are made
1279 * on how many (if any) will be written, and this function does not wait
1280 * for IO completion of submitted IO.
1281 */
1282void writeback_inodes_sb_nr(struct super_block *sb,
1283                            unsigned long nr,
1284                            enum wb_reason reason)
1285{
1286        DECLARE_COMPLETION_ONSTACK(done);
1287        struct wb_writeback_work work = {
1288                .sb                     = sb,
1289                .sync_mode              = WB_SYNC_NONE,
1290                .tagged_writepages      = 1,
1291                .done                   = &done,
1292                .nr_pages               = nr,
1293                .reason                 = reason,
1294        };
1295
1296        if (sb->s_bdi == &noop_backing_dev_info)
1297                return;
1298        WARN_ON(!rwsem_is_locked(&sb->s_umount));
1299        bdi_queue_work(sb->s_bdi, &work);
1300        wait_for_completion(&done);
1301}
1302EXPORT_SYMBOL(writeback_inodes_sb_nr);
1303
1304/**
1305 * writeback_inodes_sb  -       writeback dirty inodes from given super_block
1306 * @sb: the superblock
1307 * @reason: reason why some writeback work was initiated
1308 *
1309 * Start writeback on some inodes on this super_block. No guarantees are made
1310 * on how many (if any) will be written, and this function does not wait
1311 * for IO completion of submitted IO.
1312 */
1313void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1314{
1315        return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1316}
1317EXPORT_SYMBOL(writeback_inodes_sb);
1318
1319/**
1320 * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
1321 * @sb: the superblock
1322 * @nr: the number of pages to write
1323 * @reason: the reason of writeback
1324 *
1325 * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
1326 * Returns 1 if writeback was started, 0 if not.
1327 */
1328int try_to_writeback_inodes_sb_nr(struct super_block *sb,
1329                                  unsigned long nr,
1330                                  enum wb_reason reason)
1331{
1332        if (writeback_in_progress(sb->s_bdi))
1333                return 1;
1334
1335        if (!down_read_trylock(&sb->s_umount))
1336                return 0;
1337
1338        writeback_inodes_sb_nr(sb, nr, reason);
1339        up_read(&sb->s_umount);
1340        return 1;
1341}
1342EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
1343
1344/**
1345 * try_to_writeback_inodes_sb - try to start writeback if none underway
1346 * @sb: the superblock
1347 * @reason: reason why some writeback work was initiated
1348 *
1349 * Implement by try_to_writeback_inodes_sb_nr()
1350 * Returns 1 if writeback was started, 0 if not.
1351 */
1352int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1353{
1354        return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1355}
1356EXPORT_SYMBOL(try_to_writeback_inodes_sb);
1357
1358/**
1359 * sync_inodes_sb       -       sync sb inode pages
1360 * @sb:                 the superblock
1361 * @older_than_this:    timestamp
1362 *
1363 * This function writes and waits on any dirty inode belonging to this
1364 * superblock that has been dirtied before given timestamp.
1365 */
1366void sync_inodes_sb(struct super_block *sb, unsigned long older_than_this)
1367{
1368        DECLARE_COMPLETION_ONSTACK(done);
1369        struct wb_writeback_work work = {
1370                .sb             = sb,
1371                .sync_mode      = WB_SYNC_ALL,
1372                .nr_pages       = LONG_MAX,
1373                .older_than_this = older_than_this,
1374                .older_than_this_is_set = 1,
1375                .range_cyclic   = 0,
1376                .done           = &done,
1377                .reason         = WB_REASON_SYNC,
1378                .for_sync       = 1,
1379        };
1380
1381        /* Nothing to do? */
1382        if (sb->s_bdi == &noop_backing_dev_info)
1383                return;
1384        WARN_ON(!rwsem_is_locked(&sb->s_umount));
1385
1386        bdi_queue_work(sb->s_bdi, &work);
1387        wait_for_completion(&done);
1388
1389        wait_sb_inodes(sb);
1390}
1391EXPORT_SYMBOL(sync_inodes_sb);
1392
1393/**
1394 * write_inode_now      -       write an inode to disk
1395 * @inode: inode to write to disk
1396 * @sync: whether the write should be synchronous or not
1397 *
1398 * This function commits an inode to disk immediately if it is dirty. This is
1399 * primarily needed by knfsd.
1400 *
1401 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1402 */
1403int write_inode_now(struct inode *inode, int sync)
1404{
1405        struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1406        struct writeback_control wbc = {
1407                .nr_to_write = LONG_MAX,
1408                .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1409                .range_start = 0,
1410                .range_end = LLONG_MAX,
1411        };
1412
1413        if (!mapping_cap_writeback_dirty(inode->i_mapping))
1414                wbc.nr_to_write = 0;
1415
1416        might_sleep();
1417        return writeback_single_inode(inode, wb, &wbc);
1418}
1419EXPORT_SYMBOL(write_inode_now);
1420
1421/**
1422 * sync_inode - write an inode and its pages to disk.
1423 * @inode: the inode to sync
1424 * @wbc: controls the writeback mode
1425 *
1426 * sync_inode() will write an inode and its pages to disk.  It will also
1427 * correctly update the inode on its superblock's dirty inode lists and will
1428 * update inode->i_state.
1429 *
1430 * The caller must have a ref on the inode.
1431 */
1432int sync_inode(struct inode *inode, struct writeback_control *wbc)
1433{
1434        return writeback_single_inode(inode, &inode_to_bdi(inode)->wb, wbc);
1435}
1436EXPORT_SYMBOL(sync_inode);
1437
1438/**
1439 * sync_inode_metadata - write an inode to disk
1440 * @inode: the inode to sync
1441 * @wait: wait for I/O to complete.
1442 *
1443 * Write an inode to disk and adjust its dirty state after completion.
1444 *
1445 * Note: only writes the actual inode, no associated data or other metadata.
1446 */
1447int sync_inode_metadata(struct inode *inode, int wait)
1448{
1449        struct writeback_control wbc = {
1450                .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1451                .nr_to_write = 0, /* metadata-only */
1452        };
1453
1454        return sync_inode(inode, &wbc);
1455}
1456EXPORT_SYMBOL(sync_inode_metadata);
1457