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