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