xfs_sync.c

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/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_types.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.h"
#include "xfs_trans_priv.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_inode.h"
#include "xfs_dinode.h"
#include "xfs_error.h"
#include "xfs_filestream.h"
#include "xfs_vnodeops.h"
#include "xfs_inode_item.h"
#include "xfs_quota.h"
#include "xfs_trace.h"
#include "xfs_fsops.h"

#include <linux/kthread.h>
#include <linux/freezer.h>

struct workqueue_struct *xfs_syncd_wq;  /* sync workqueue */

/*
 * The inode lookup is done in batches to keep the amount of lock traffic and
 * radix tree lookups to a minimum. The batch size is a trade off between
 * lookup reduction and stack usage. This is in the reclaim path, so we can't
 * be too greedy.
 */
#define XFS_LOOKUP_BATCH    32

STATIC int
xfs_inode_ag_walk_grab(
    struct xfs_inode    *ip)
{
    struct inode        *inode = VFS_I(ip);

    ASSERT(rcu_read_lock_held());

    /*
     * check for stale RCU freed inode
     *
     * If the inode has been reallocated, it doesn't matter if it's not in
     * the AG we are walking - we are walking for writeback, so if it
     * passes all the "valid inode" checks and is dirty, then we'll write
     * it back anyway.  If it has been reallocated and still being
     * initialised, the XFS_INEW check below will catch it.
     */
    spin_lock(&ip->i_flags_lock);
    if (!ip->i_ino)
        goto out_unlock_noent;

    /* avoid new or reclaimable inodes. Leave for reclaim code to flush */
    if (__xfs_iflags_test(ip, XFS_INEW | XFS_IRECLAIMABLE | XFS_IRECLAIM))
        goto out_unlock_noent;
    spin_unlock(&ip->i_flags_lock);

    /* nothing to sync during shutdown */
    if (XFS_FORCED_SHUTDOWN(ip->i_mount))
        return EFSCORRUPTED;

    /* If we can't grab the inode, it must on it's way to reclaim. */
    if (!igrab(inode))
        return ENOENT;

    if (is_bad_inode(inode)) {
        IRELE(ip);
        return ENOENT;
    }

    /* inode is valid */
    return 0;

out_unlock_noent:
    spin_unlock(&ip->i_flags_lock);
    return ENOENT;
}

STATIC int
xfs_inode_ag_walk(
    struct xfs_mount    *mp,
    struct xfs_perag    *pag,
    int         (*execute)(struct xfs_inode *ip,
                       struct xfs_perag *pag, int flags),
    int         flags)
{
    uint32_t        first_index;
    int         last_error = 0;
    int         skipped;
    int         done;
    int         nr_found;

restart:
    done = 0;
    skipped = 0;
    first_index = 0;
    nr_found = 0;
    do {
        struct xfs_inode *batch[XFS_LOOKUP_BATCH];
        int     error = 0;
        int     i;

        rcu_read_lock();
        nr_found = radix_tree_gang_lookup(&pag->pag_ici_root,
                    (void **)batch, first_index,
                    XFS_LOOKUP_BATCH);
        if (!nr_found) {
            rcu_read_unlock();
            break;
        }

        /*
         * Grab the inodes before we drop the lock. if we found
         * nothing, nr == 0 and the loop will be skipped.
         */
        for (i = 0; i < nr_found; i++) {
            struct xfs_inode *ip = batch[i];

            if (done || xfs_inode_ag_walk_grab(ip))
                batch[i] = NULL;

            /*
             * Update the index for the next lookup. Catch
             * overflows into the next AG range which can occur if
             * we have inodes in the last block of the AG and we
             * are currently pointing to the last inode.
             *
             * Because we may see inodes that are from the wrong AG
             * due to RCU freeing and reallocation, only update the
             * index if it lies in this AG. It was a race that lead
             * us to see this inode, so another lookup from the
             * same index will not find it again.
             */
            if (XFS_INO_TO_AGNO(mp, ip->i_ino) != pag->pag_agno)
                continue;
            first_index = XFS_INO_TO_AGINO(mp, ip->i_ino + 1);
            if (first_index < XFS_INO_TO_AGINO(mp, ip->i_ino))
                done = 1;
        }

        /* unlock now we've grabbed the inodes. */
        rcu_read_unlock();

        for (i = 0; i < nr_found; i++) {
            if (!batch[i])
                continue;
            error = execute(batch[i], pag, flags);
            IRELE(batch[i]);
            if (error == EAGAIN) {
                skipped++;
                continue;
            }
            if (error && last_error != EFSCORRUPTED)
                last_error = error;
        }

        /* bail out if the filesystem is corrupted.  */
        if (error == EFSCORRUPTED)
            break;

        cond_resched();

    } while (nr_found && !done);

    if (skipped) {
        delay(1);
        goto restart;
    }
    return last_error;
}

int
xfs_inode_ag_iterator(
    struct xfs_mount    *mp,
    int         (*execute)(struct xfs_inode *ip,
                       struct xfs_perag *pag, int flags),
    int         flags)
{
    struct xfs_perag    *pag;
    int         error = 0;
    int         last_error = 0;
    xfs_agnumber_t      ag;

    ag = 0;
    while ((pag = xfs_perag_get(mp, ag))) {
        ag = pag->pag_agno + 1;
        error = xfs_inode_ag_walk(mp, pag, execute, flags);
        xfs_perag_put(pag);
        if (error) {
            last_error = error;
            if (error == EFSCORRUPTED)
                break;
        }
    }
    return XFS_ERROR(last_error);
}

STATIC int
xfs_sync_inode_data(
    struct xfs_inode    *ip,
    struct xfs_perag    *pag,
    int         flags)
{
    struct inode        *inode = VFS_I(ip);
    struct address_space *mapping = inode->i_mapping;
    int         error = 0;

    if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
        return 0;

    if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED)) {
        if (flags & SYNC_TRYLOCK)
            return 0;
        xfs_ilock(ip, XFS_IOLOCK_SHARED);
    }

    error = xfs_flush_pages(ip, 0, -1, (flags & SYNC_WAIT) ?
                0 : XBF_ASYNC, FI_NONE);
    xfs_iunlock(ip, XFS_IOLOCK_SHARED);
    return error;
}

/*
 * Write out pagecache data for the whole filesystem.
 */
STATIC int
xfs_sync_data(
    struct xfs_mount    *mp,
    int         flags)
{
    int         error;

    ASSERT((flags & ~(SYNC_TRYLOCK|SYNC_WAIT)) == 0);

    error = xfs_inode_ag_iterator(mp, xfs_sync_inode_data, flags);
    if (error)
        return XFS_ERROR(error);

    xfs_log_force(mp, (flags & SYNC_WAIT) ? XFS_LOG_SYNC : 0);
    return 0;
}

STATIC int
xfs_sync_fsdata(
    struct xfs_mount    *mp)
{
    struct xfs_buf      *bp;
    int         error;

    /*
     * If the buffer is pinned then push on the log so we won't get stuck
     * waiting in the write for someone, maybe ourselves, to flush the log.
     *
     * Even though we just pushed the log above, we did not have the
     * superblock buffer locked at that point so it can become pinned in
     * between there and here.
     */
    bp = xfs_getsb(mp, 0);
    if (xfs_buf_ispinned(bp))
        xfs_log_force(mp, 0);
    error = xfs_bwrite(bp);
    xfs_buf_relse(bp);
    return error;
}

/*
 * When remounting a filesystem read-only or freezing the filesystem, we have
 * two phases to execute. This first phase is syncing the data before we
 * quiesce the filesystem, and the second is flushing all the inodes out after
 * we've waited for all the transactions created by the first phase to
 * complete. The second phase ensures that the inodes are written to their
 * location on disk rather than just existing in transactions in the log. This
 * means after a quiesce there is no log replay required to write the inodes to
 * disk (this is the main difference between a sync and a quiesce).
 */
/*
 * First stage of freeze - no writers will make progress now we are here,
 * so we flush delwri and delalloc buffers here, then wait for all I/O to
 * complete.  Data is frozen at that point. Metadata is not frozen,
 * transactions can still occur here so don't bother emptying the AIL
 * because it'll just get dirty again.
 */
int
xfs_quiesce_data(
    struct xfs_mount    *mp)
{
    int         error, error2 = 0;

    /* force out the log */
    xfs_log_force(mp, XFS_LOG_SYNC);

    /* write superblock and hoover up shutdown errors */
    error = xfs_sync_fsdata(mp);

    /* mark the log as covered if needed */
    if (xfs_log_need_covered(mp))
        error2 = xfs_fs_log_dummy(mp);

    return error ? error : error2;
}

/*
 * Second stage of a quiesce. The data is already synced, now we have to take
 * care of the metadata. New transactions are already blocked, so we need to
 * wait for any remaining transactions to drain out before proceeding.
 */
void
xfs_quiesce_attr(
    struct xfs_mount    *mp)
{
    int error = 0;

    /* wait for all modifications to complete */
    while (atomic_read(&mp->m_active_trans) > 0)
        delay(100);

    /* reclaim inodes to do any IO before the freeze completes */
    xfs_reclaim_inodes(mp, 0);
    xfs_reclaim_inodes(mp, SYNC_WAIT);

    /* flush all pending changes from the AIL */
    xfs_ail_push_all_sync(mp->m_ail);

    /*
     * Just warn here till VFS can correctly support
     * read-only remount without racing.
     */
    WARN_ON(atomic_read(&mp->m_active_trans) != 0);

    /* Push the superblock and write an unmount record */
    error = xfs_log_sbcount(mp);
    if (error)
        xfs_warn(mp, "xfs_attr_quiesce: failed to log sb changes. "
                "Frozen image may not be consistent.");
    xfs_log_unmount_write(mp);

    /*
     * At this point we might have modified the superblock again and thus
     * added an item to the AIL, thus flush it again.
     */
    xfs_ail_push_all_sync(mp->m_ail);

    /*
     * The superblock buffer is uncached and xfsaild_push() will lock and
     * set the XBF_ASYNC flag on the buffer. We cannot do xfs_buf_iowait()
     * here but a lock on the superblock buffer will block until iodone()
     * has completed.
     */
    xfs_buf_lock(mp->m_sb_bp);
    xfs_buf_unlock(mp->m_sb_bp);
}

static void
xfs_syncd_queue_sync(
    struct xfs_mount        *mp)
{
    queue_delayed_work(xfs_syncd_wq, &mp->m_sync_work,
                msecs_to_jiffies(xfs_syncd_centisecs * 10));
}

/*
 * Every sync period we need to unpin all items, reclaim inodes and sync
 * disk quotas.  We might need to cover the log to indicate that the
 * filesystem is idle and not frozen.
 */
STATIC void
xfs_sync_worker(
    struct work_struct *work)
{
    struct xfs_mount *mp = container_of(to_delayed_work(work),
                    struct xfs_mount, m_sync_work);
    int     error;

    /*
     * We shouldn't write/force the log if we are in the mount/unmount
     * process or on a read only filesystem. The workqueue still needs to be
     * active in both cases, however, because it is used for inode reclaim
     * during these times.  Use the MS_ACTIVE flag to avoid doing anything
     * during mount.  Doing work during unmount is avoided by calling
     * cancel_delayed_work_sync on this work queue before tearing down
     * the ail and the log in xfs_log_unmount.
     */
    if (!(mp->m_super->s_flags & MS_ACTIVE) &&
        !(mp->m_flags & XFS_MOUNT_RDONLY)) {
        /* dgc: errors ignored here */
        if (mp->m_super->s_writers.frozen == SB_UNFROZEN &&
            xfs_log_need_covered(mp))
            error = xfs_fs_log_dummy(mp);
        else
            xfs_log_force(mp, 0);

        /* start pushing all the metadata that is currently
         * dirty */
        xfs_ail_push_all(mp->m_ail);
    }

    /* queue us up again */
    xfs_syncd_queue_sync(mp);
}

/*
 * Queue a new inode reclaim pass if there are reclaimable inodes and there
 * isn't a reclaim pass already in progress. By default it runs every 5s based
 * on the xfs syncd work default of 30s. Perhaps this should have it's own
 * tunable, but that can be done if this method proves to be ineffective or too
 * aggressive.
 */
static void
xfs_syncd_queue_reclaim(
    struct xfs_mount        *mp)
{

    rcu_read_lock();
    if (radix_tree_tagged(&mp->m_perag_tree, XFS_ICI_RECLAIM_TAG)) {
        queue_delayed_work(xfs_syncd_wq, &mp->m_reclaim_work,
            msecs_to_jiffies(xfs_syncd_centisecs / 6 * 10));
    }
    rcu_read_unlock();
}

/*
 * This is a fast pass over the inode cache to try to get reclaim moving on as
 * many inodes as possible in a short period of time. It kicks itself every few
 * seconds, as well as being kicked by the inode cache shrinker when memory
 * goes low. It scans as quickly as possible avoiding locked inodes or those
 * already being flushed, and once done schedules a future pass.
 */
STATIC void
xfs_reclaim_worker(
    struct work_struct *work)
{
    struct xfs_mount *mp = container_of(to_delayed_work(work),
                    struct xfs_mount, m_reclaim_work);

    xfs_reclaim_inodes(mp, SYNC_TRYLOCK);
    xfs_syncd_queue_reclaim(mp);
}

/*
 * Flush delayed allocate data, attempting to free up reserved space
 * from existing allocations.  At this point a new allocation attempt
 * has failed with ENOSPC and we are in the process of scratching our
 * heads, looking about for more room.
 *
 * Queue a new data flush if there isn't one already in progress and
 * wait for completion of the flush. This means that we only ever have one
 * inode flush in progress no matter how many ENOSPC events are occurring and
 * so will prevent the system from bogging down due to every concurrent
 * ENOSPC event scanning all the active inodes in the system for writeback.
 */
void
xfs_flush_inodes(
    struct xfs_inode    *ip)
{
    struct xfs_mount    *mp = ip->i_mount;

    queue_work(xfs_syncd_wq, &mp->m_flush_work);
    flush_work(&mp->m_flush_work);
}

STATIC void
xfs_flush_worker(
    struct work_struct *work)
{
    struct xfs_mount *mp = container_of(work,
                    struct xfs_mount, m_flush_work);

    xfs_sync_data(mp, SYNC_TRYLOCK);
    xfs_sync_data(mp, SYNC_TRYLOCK | SYNC_WAIT);
}

int
xfs_syncd_init(
    struct xfs_mount    *mp)
{
    INIT_WORK(&mp->m_flush_work, xfs_flush_worker);
    INIT_DELAYED_WORK(&mp->m_sync_work, xfs_sync_worker);
    INIT_DELAYED_WORK(&mp->m_reclaim_work, xfs_reclaim_worker);

    xfs_syncd_queue_sync(mp);

    return 0;
}

void
xfs_syncd_stop(
    struct xfs_mount    *mp)
{
    cancel_delayed_work_sync(&mp->m_sync_work);
    cancel_delayed_work_sync(&mp->m_reclaim_work);
    cancel_work_sync(&mp->m_flush_work);
}

void
__xfs_inode_set_reclaim_tag(
    struct xfs_perag    *pag,
    struct xfs_inode    *ip)
{
    radix_tree_tag_set(&pag->pag_ici_root,
               XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
               XFS_ICI_RECLAIM_TAG);

    if (!pag->pag_ici_reclaimable) {
        /* propagate the reclaim tag up into the perag radix tree */
        spin_lock(&ip->i_mount->m_perag_lock);
        radix_tree_tag_set(&ip->i_mount->m_perag_tree,
                XFS_INO_TO_AGNO(ip->i_mount, ip->i_ino),
                XFS_ICI_RECLAIM_TAG);
        spin_unlock(&ip->i_mount->m_perag_lock);

        /* schedule periodic background inode reclaim */
        xfs_syncd_queue_reclaim(ip->i_mount);

        trace_xfs_perag_set_reclaim(ip->i_mount, pag->pag_agno,
                            -1, _RET_IP_);
    }
    pag->pag_ici_reclaimable++;
}

/*
 * We set the inode flag atomically with the radix tree tag.
 * Once we get tag lookups on the radix tree, this inode flag
 * can go away.
 */
void
xfs_inode_set_reclaim_tag(
    xfs_inode_t *ip)
{
    struct xfs_mount *mp = ip->i_mount;
    struct xfs_perag *pag;

    pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
    spin_lock(&pag->pag_ici_lock);
    spin_lock(&ip->i_flags_lock);
    __xfs_inode_set_reclaim_tag(pag, ip);
    __xfs_iflags_set(ip, XFS_IRECLAIMABLE);
    spin_unlock(&ip->i_flags_lock);
    spin_unlock(&pag->pag_ici_lock);
    xfs_perag_put(pag);
}

STATIC void
__xfs_inode_clear_reclaim(
    xfs_perag_t *pag,
    xfs_inode_t *ip)
{
    pag->pag_ici_reclaimable--;
    if (!pag->pag_ici_reclaimable) {
        /* clear the reclaim tag from the perag radix tree */
        spin_lock(&ip->i_mount->m_perag_lock);
        radix_tree_tag_clear(&ip->i_mount->m_perag_tree,
                XFS_INO_TO_AGNO(ip->i_mount, ip->i_ino),
                XFS_ICI_RECLAIM_TAG);
        spin_unlock(&ip->i_mount->m_perag_lock);
        trace_xfs_perag_clear_reclaim(ip->i_mount, pag->pag_agno,
                            -1, _RET_IP_);
    }
}

void
__xfs_inode_clear_reclaim_tag(
    xfs_mount_t *mp,
    xfs_perag_t *pag,
    xfs_inode_t *ip)
{
    radix_tree_tag_clear(&pag->pag_ici_root,
            XFS_INO_TO_AGINO(mp, ip->i_ino), XFS_ICI_RECLAIM_TAG);
    __xfs_inode_clear_reclaim(pag, ip);
}

/*
 * Grab the inode for reclaim exclusively.
 * Return 0 if we grabbed it, non-zero otherwise.
 */
STATIC int
xfs_reclaim_inode_grab(
    struct xfs_inode    *ip,
    int         flags)
{
    ASSERT(rcu_read_lock_held());

    /* quick check for stale RCU freed inode */
    if (!ip->i_ino)
        return 1;

    /*
     * If we are asked for non-blocking operation, do unlocked checks to
     * see if the inode already is being flushed or in reclaim to avoid
     * lock traffic.
     */
    if ((flags & SYNC_TRYLOCK) &&
        __xfs_iflags_test(ip, XFS_IFLOCK | XFS_IRECLAIM))
        return 1;

    /*
     * The radix tree lock here protects a thread in xfs_iget from racing
     * with us starting reclaim on the inode.  Once we have the
     * XFS_IRECLAIM flag set it will not touch us.
     *
     * Due to RCU lookup, we may find inodes that have been freed and only
     * have XFS_IRECLAIM set.  Indeed, we may see reallocated inodes that
     * aren't candidates for reclaim at all, so we must check the
     * XFS_IRECLAIMABLE is set first before proceeding to reclaim.
     */
    spin_lock(&ip->i_flags_lock);
    if (!__xfs_iflags_test(ip, XFS_IRECLAIMABLE) ||
        __xfs_iflags_test(ip, XFS_IRECLAIM)) {
        /* not a reclaim candidate. */
        spin_unlock(&ip->i_flags_lock);
        return 1;
    }
    __xfs_iflags_set(ip, XFS_IRECLAIM);
    spin_unlock(&ip->i_flags_lock);
    return 0;
}

/*
 * Inodes in different states need to be treated differently. The following
 * table lists the inode states and the reclaim actions necessary:
 *
 *  inode state      iflush ret     required action
 *      ---------------      ----------         ---------------
 *  bad         -       reclaim
 *  shutdown        EIO     unpin and reclaim
 *  clean, unpinned     0       reclaim
 *  stale, unpinned     0       reclaim
 *  clean, pinned(*)    0       requeue
 *  stale, pinned       EAGAIN      requeue
 *  dirty, async        -       requeue
 *  dirty, sync     0       reclaim
 *
 * (*) dgc: I don't think the clean, pinned state is possible but it gets
 * handled anyway given the order of checks implemented.
 *
 * Also, because we get the flush lock first, we know that any inode that has
 * been flushed delwri has had the flush completed by the time we check that
 * the inode is clean.
 *
 * Note that because the inode is flushed delayed write by AIL pushing, the
 * flush lock may already be held here and waiting on it can result in very
 * long latencies.  Hence for sync reclaims, where we wait on the flush lock,
 * the caller should push the AIL first before trying to reclaim inodes to
 * minimise the amount of time spent waiting.  For background relaim, we only
 * bother to reclaim clean inodes anyway.
 *
 * Hence the order of actions after gaining the locks should be:
 *  bad     => reclaim
 *  shutdown    => unpin and reclaim
 *  pinned, async   => requeue
 *  pinned, sync    => unpin
 *  stale       => reclaim
 *  clean       => reclaim
 *  dirty, async    => requeue
 *  dirty, sync => flush, wait and reclaim
 */
STATIC int
xfs_reclaim_inode(
    struct xfs_inode    *ip,
    struct xfs_perag    *pag,
    int         sync_mode)
{
    struct xfs_buf      *bp = NULL;
    int         error;

restart:
    error = 0;
    xfs_ilock(ip, XFS_ILOCK_EXCL);
    if (!xfs_iflock_nowait(ip)) {
        if (!(sync_mode & SYNC_WAIT))
            goto out;
        xfs_iflock(ip);
    }

    if (is_bad_inode(VFS_I(ip)))
        goto reclaim;
    if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
        xfs_iunpin_wait(ip);
        xfs_iflush_abort(ip, false);
        goto reclaim;
    }
    if (xfs_ipincount(ip)) {
        if (!(sync_mode & SYNC_WAIT))
            goto out_ifunlock;
        xfs_iunpin_wait(ip);
    }
    if (xfs_iflags_test(ip, XFS_ISTALE))
        goto reclaim;
    if (xfs_inode_clean(ip))
        goto reclaim;

    /*
     * Never flush out dirty data during non-blocking reclaim, as it would
     * just contend with AIL pushing trying to do the same job.
     */
    if (!(sync_mode & SYNC_WAIT))
        goto out_ifunlock;

    /*
     * Now we have an inode that needs flushing.
     *
     * Note that xfs_iflush will never block on the inode buffer lock, as
     * xfs_ifree_cluster() can lock the inode buffer before it locks the
     * ip->i_lock, and we are doing the exact opposite here.  As a result,
     * doing a blocking xfs_imap_to_bp() to get the cluster buffer would
     * result in an ABBA deadlock with xfs_ifree_cluster().
     *
     * As xfs_ifree_cluser() must gather all inodes that are active in the
     * cache to mark them stale, if we hit this case we don't actually want
     * to do IO here - we want the inode marked stale so we can simply
     * reclaim it.  Hence if we get an EAGAIN error here,  just unlock the
     * inode, back off and try again.  Hopefully the next pass through will
     * see the stale flag set on the inode.
     */
    error = xfs_iflush(ip, &bp);
    if (error == EAGAIN) {
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        /* backoff longer than in xfs_ifree_cluster */
        delay(2);
        goto restart;
    }

    if (!error) {
        error = xfs_bwrite(bp);
        xfs_buf_relse(bp);
    }

    xfs_iflock(ip);
reclaim:
    xfs_ifunlock(ip);
    xfs_iunlock(ip, XFS_ILOCK_EXCL);

    XFS_STATS_INC(xs_ig_reclaims);
    /*
     * Remove the inode from the per-AG radix tree.
     *
     * Because radix_tree_delete won't complain even if the item was never
     * added to the tree assert that it's been there before to catch
     * problems with the inode life time early on.
     */
    spin_lock(&pag->pag_ici_lock);
    if (!radix_tree_delete(&pag->pag_ici_root,
                XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino)))
        ASSERT(0);
    __xfs_inode_clear_reclaim(pag, ip);
    spin_unlock(&pag->pag_ici_lock);

    /*
     * Here we do an (almost) spurious inode lock in order to coordinate
     * with inode cache radix tree lookups.  This is because the lookup
     * can reference the inodes in the cache without taking references.
     *
     * We make that OK here by ensuring that we wait until the inode is
     * unlocked after the lookup before we go ahead and free it.
     */
    xfs_ilock(ip, XFS_ILOCK_EXCL);
    xfs_qm_dqdetach(ip);
    xfs_iunlock(ip, XFS_ILOCK_EXCL);

    xfs_inode_free(ip);
    return error;

out_ifunlock:
    xfs_ifunlock(ip);
out:
    xfs_iflags_clear(ip, XFS_IRECLAIM);
    xfs_iunlock(ip, XFS_ILOCK_EXCL);
    /*
     * We could return EAGAIN here to make reclaim rescan the inode tree in
     * a short while. However, this just burns CPU time scanning the tree
     * waiting for IO to complete and xfssyncd never goes back to the idle
     * state. Instead, return 0 to let the next scheduled background reclaim
     * attempt to reclaim the inode again.
     */
    return 0;
}

/*
 * Walk the AGs and reclaim the inodes in them. Even if the filesystem is
 * corrupted, we still want to try to reclaim all the inodes. If we don't,
 * then a shut down during filesystem unmount reclaim walk leak all the
 * unreclaimed inodes.
 */
int
xfs_reclaim_inodes_ag(
    struct xfs_mount    *mp,
    int         flags,
    int         *nr_to_scan)
{
    struct xfs_perag    *pag;
    int         error = 0;
    int         last_error = 0;
    xfs_agnumber_t      ag;
    int         trylock = flags & SYNC_TRYLOCK;
    int         skipped;

restart:
    ag = 0;
    skipped = 0;
    while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
        unsigned long   first_index = 0;
        int     done = 0;
        int     nr_found = 0;

        ag = pag->pag_agno + 1;

        if (trylock) {
            if (!mutex_trylock(&pag->pag_ici_reclaim_lock)) {
                skipped++;
                xfs_perag_put(pag);
                continue;
            }
            first_index = pag->pag_ici_reclaim_cursor;
        } else
            mutex_lock(&pag->pag_ici_reclaim_lock);

        do {
            struct xfs_inode *batch[XFS_LOOKUP_BATCH];
            int i;

            rcu_read_lock();
            nr_found = radix_tree_gang_lookup_tag(
                    &pag->pag_ici_root,
                    (void **)batch, first_index,
                    XFS_LOOKUP_BATCH,
                    XFS_ICI_RECLAIM_TAG);
            if (!nr_found) {
                done = 1;
                rcu_read_unlock();
                break;
            }

            /*
             * Grab the inodes before we drop the lock. if we found
             * nothing, nr == 0 and the loop will be skipped.
             */
            for (i = 0; i < nr_found; i++) {
                struct xfs_inode *ip = batch[i];

                if (done || xfs_reclaim_inode_grab(ip, flags))
                    batch[i] = NULL;

                /*
                 * Update the index for the next lookup. Catch
                 * overflows into the next AG range which can
                 * occur if we have inodes in the last block of
                 * the AG and we are currently pointing to the
                 * last inode.
                 *
                 * Because we may see inodes that are from the
                 * wrong AG due to RCU freeing and
                 * reallocation, only update the index if it
                 * lies in this AG. It was a race that lead us
                 * to see this inode, so another lookup from
                 * the same index will not find it again.
                 */
                if (XFS_INO_TO_AGNO(mp, ip->i_ino) !=
                                pag->pag_agno)
                    continue;
                first_index = XFS_INO_TO_AGINO(mp, ip->i_ino + 1);
                if (first_index < XFS_INO_TO_AGINO(mp, ip->i_ino))
                    done = 1;
            }

            /* unlock now we've grabbed the inodes. */
            rcu_read_unlock();

            for (i = 0; i < nr_found; i++) {
                if (!batch[i])
                    continue;
                error = xfs_reclaim_inode(batch[i], pag, flags);
                if (error && last_error != EFSCORRUPTED)
                    last_error = error;
            }

            *nr_to_scan -= XFS_LOOKUP_BATCH;

            cond_resched();

        } while (nr_found && !done && *nr_to_scan > 0);

        if (trylock && !done)
            pag->pag_ici_reclaim_cursor = first_index;
        else
            pag->pag_ici_reclaim_cursor = 0;
        mutex_unlock(&pag->pag_ici_reclaim_lock);
        xfs_perag_put(pag);
    }

    /*
     * if we skipped any AG, and we still have scan count remaining, do
     * another pass this time using blocking reclaim semantics (i.e
     * waiting on the reclaim locks and ignoring the reclaim cursors). This
     * ensure that when we get more reclaimers than AGs we block rather
     * than spin trying to execute reclaim.
     */
    if (skipped && (flags & SYNC_WAIT) && *nr_to_scan > 0) {
        trylock = 0;
        goto restart;
    }
    return XFS_ERROR(last_error);
}

int
xfs_reclaim_inodes(
    xfs_mount_t *mp,
    int     mode)
{
    int     nr_to_scan = INT_MAX;

    return xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
}

/*
 * Scan a certain number of inodes for reclaim.
 *
 * When called we make sure that there is a background (fast) inode reclaim in
 * progress, while we will throttle the speed of reclaim via doing synchronous
 * reclaim of inodes. That means if we come across dirty inodes, we wait for
 * them to be cleaned, which we hope will not be very long due to the
 * background walker having already kicked the IO off on those dirty inodes.
 */
void
xfs_reclaim_inodes_nr(
    struct xfs_mount    *mp,
    int         nr_to_scan)
{
    /* kick background reclaimer and push the AIL */
    xfs_syncd_queue_reclaim(mp);
    xfs_ail_push_all(mp->m_ail);

    xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK | SYNC_WAIT, &nr_to_scan);
}

/*
 * Return the number of reclaimable inodes in the filesystem for
 * the shrinker to determine how much to reclaim.
 */
int
xfs_reclaim_inodes_count(
    struct xfs_mount    *mp)
{
    struct xfs_perag    *pag;
    xfs_agnumber_t      ag = 0;
    int         reclaimable = 0;

    while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
        ag = pag->pag_agno + 1;
        reclaimable += pag->pag_ici_reclaimable;
        xfs_perag_put(pag);
    }
    return reclaimable;
}