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