xfs: simplify inode to transaction joining

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / fs / xfs / linux-2.6 / xfs_sync.c

/*
 * 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_bit.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.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 <linux/kthread.h>
#include <linux/freezer.h>


STATIC xfs_inode_t *
xfs_inode_ag_lookup(
        struct xfs_mount        *mp,
        struct xfs_perag        *pag,
        uint32_t                *first_index,
        int                     tag)
{
        int                     nr_found;
        struct xfs_inode        *ip;

        /*
         * use a gang lookup to find the next inode in the tree
         * as the tree is sparse and a gang lookup walks to find
         * the number of objects requested.
         */
        if (tag == XFS_ICI_NO_TAG) {
                nr_found = radix_tree_gang_lookup(&pag->pag_ici_root,
                                (void **)&ip, *first_index, 1);
        } else {
                nr_found = radix_tree_gang_lookup_tag(&pag->pag_ici_root,
                                (void **)&ip, *first_index, 1, tag);
        }
        if (!nr_found)
                return 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.
         */
        *first_index = XFS_INO_TO_AGINO(mp, ip->i_ino + 1);
        if (*first_index < XFS_INO_TO_AGINO(mp, ip->i_ino))
                return NULL;
        return ip;
}

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,
        int                     tag,
        int                     exclusive,
        int                     *nr_to_scan)
{
        uint32_t                first_index;
        int                     last_error = 0;
        int                     skipped;

restart:
        skipped = 0;
        first_index = 0;
        do {
                int             error = 0;
                xfs_inode_t     *ip;

                if (exclusive)
                        write_lock(&pag->pag_ici_lock);
                else
                        read_lock(&pag->pag_ici_lock);
                ip = xfs_inode_ag_lookup(mp, pag, &first_index, tag);
                if (!ip) {
                        if (exclusive)
                                write_unlock(&pag->pag_ici_lock);
                        else
                                read_unlock(&pag->pag_ici_lock);
                        break;
                }

                /* execute releases pag->pag_ici_lock */
                error = execute(ip, pag, flags);
                if (error == EAGAIN) {
                        skipped++;
                        continue;
                }
                if (error)
                        last_error = error;

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

        } while ((*nr_to_scan)--);

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

/*
 * Select the next per-ag structure to iterate during the walk. The reclaim
 * walk is optimised only to walk AGs with reclaimable inodes in them.
 */
static struct xfs_perag *
xfs_inode_ag_iter_next_pag(
        struct xfs_mount        *mp,
        xfs_agnumber_t          *first,
        int                     tag)
{
        struct xfs_perag        *pag = NULL;

        if (tag == XFS_ICI_RECLAIM_TAG) {
                int found;
                int ref;

                spin_lock(&mp->m_perag_lock);
                found = radix_tree_gang_lookup_tag(&mp->m_perag_tree,
                                (void **)&pag, *first, 1, tag);
                if (found <= 0) {
                        spin_unlock(&mp->m_perag_lock);
                        return NULL;
                }
                *first = pag->pag_agno + 1;
                /* open coded pag reference increment */
                ref = atomic_inc_return(&pag->pag_ref);
                spin_unlock(&mp->m_perag_lock);
                trace_xfs_perag_get_reclaim(mp, pag->pag_agno, ref, _RET_IP_);
        } else {
                pag = xfs_perag_get(mp, *first);
                (*first)++;
        }
        return pag;
}

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

        nr = nr_to_scan ? *nr_to_scan : INT_MAX;
        ag = 0;
        while ((pag = xfs_inode_ag_iter_next_pag(mp, &ag, tag))) {
                error = xfs_inode_ag_walk(mp, pag, execute, flags, tag,
                                                exclusive, &nr);
                xfs_perag_put(pag);
                if (error) {
                        last_error = error;
                        if (error == EFSCORRUPTED)
                                break;
                }
                if (nr <= 0)
                        break;
        }
        if (nr_to_scan)
                *nr_to_scan = nr;
        return XFS_ERROR(last_error);
}

/* must be called with pag_ici_lock held and releases it */
int
xfs_sync_inode_valid(
        struct xfs_inode        *ip,
        struct xfs_perag        *pag)
{
        struct inode            *inode = VFS_I(ip);
        int                     error = EFSCORRUPTED;

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

        /* avoid new or reclaimable inodes. Leave for reclaim code to flush */
        error = ENOENT;
        if (xfs_iflags_test(ip, XFS_INEW | XFS_IRECLAIMABLE | XFS_IRECLAIM))
                goto out_unlock;

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

        if (is_bad_inode(inode)) {
                IRELE(ip);
                goto out_unlock;
        }

        /* inode is valid */
        error = 0;
out_unlock:
        read_unlock(&pag->pag_ici_lock);
        return 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;

        error = xfs_sync_inode_valid(ip, pag);
        if (error)
                return error;

        if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
                goto out_wait;

        if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED)) {
                if (flags & SYNC_TRYLOCK)
                        goto out_wait;
                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);

 out_wait:
        if (flags & SYNC_WAIT)
                xfs_ioend_wait(ip);
        IRELE(ip);
        return error;
}

STATIC int
xfs_sync_inode_attr(
        struct xfs_inode        *ip,
        struct xfs_perag        *pag,
        int                     flags)
{
        int                     error = 0;

        error = xfs_sync_inode_valid(ip, pag);
        if (error)
                return error;

        xfs_ilock(ip, XFS_ILOCK_SHARED);
        if (xfs_inode_clean(ip))
                goto out_unlock;
        if (!xfs_iflock_nowait(ip)) {
                if (!(flags & SYNC_WAIT))
                        goto out_unlock;
                xfs_iflock(ip);
        }

        if (xfs_inode_clean(ip)) {
                xfs_ifunlock(ip);
                goto out_unlock;
        }

        error = xfs_iflush(ip, flags);

 out_unlock:
        xfs_iunlock(ip, XFS_ILOCK_SHARED);
        IRELE(ip);
        return error;
}

/*
 * Write out pagecache data for the whole filesystem.
 */
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,
                                      XFS_ICI_NO_TAG, 0, NULL);
        if (error)
                return XFS_ERROR(error);

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

/*
 * Write out inode metadata (attributes) for the whole filesystem.
 */
int
xfs_sync_attr(
        struct xfs_mount        *mp,
        int                     flags)
{
        ASSERT((flags & ~SYNC_WAIT) == 0);

        return xfs_inode_ag_iterator(mp, xfs_sync_inode_attr, flags,
                                     XFS_ICI_NO_TAG, 0, NULL);
}

STATIC int
xfs_commit_dummy_trans(
        struct xfs_mount        *mp,
        uint                    flags)
{
        struct xfs_inode        *ip = mp->m_rootip;
        struct xfs_trans        *tp;
        int                     error;

        /*
         * Put a dummy transaction in the log to tell recovery
         * that all others are OK.
         */
        tp = xfs_trans_alloc(mp, XFS_TRANS_DUMMY1);
        error = xfs_trans_reserve(tp, 0, XFS_ICHANGE_LOG_RES(mp), 0, 0, 0);
        if (error) {
                xfs_trans_cancel(tp, 0);
                return error;
        }

        xfs_ilock(ip, XFS_ILOCK_EXCL);

        xfs_trans_ijoin(tp, ip);
        xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
        error = xfs_trans_commit(tp, 0);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);

        /* the log force ensures this transaction is pushed to disk */
        xfs_log_force(mp, (flags & SYNC_WAIT) ? XFS_LOG_SYNC : 0);
        return error;
}

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

        /*
         * 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);

        return xfs_bwrite(mp, bp);
}

/*
 * 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 flushing the buftarg
 * because it'll just get dirty again.
 */
int
xfs_quiesce_data(
        struct xfs_mount        *mp)
{
        int                     error, error2 = 0;

        /* push non-blocking */
        xfs_sync_data(mp, 0);
        xfs_qm_sync(mp, SYNC_TRYLOCK);

        /* push and block till complete */
        xfs_sync_data(mp, SYNC_WAIT);
        xfs_qm_sync(mp, SYNC_WAIT);

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

        /* make sure all delwri buffers are written out */
        xfs_flush_buftarg(mp->m_ddev_targp, 1);

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

        /* flush data-only devices */
        if (mp->m_rtdev_targp)
                XFS_bflush(mp->m_rtdev_targp);

        return error ? error : error2;
}

STATIC void
xfs_quiesce_fs(
        struct xfs_mount        *mp)
{
        int     count = 0, pincount;

        xfs_reclaim_inodes(mp, 0);
        xfs_flush_buftarg(mp->m_ddev_targp, 0);

        /*
         * This loop must run at least twice.  The first instance of the loop
         * will flush most meta data but that will generate more meta data
         * (typically directory updates).  Which then must be flushed and
         * logged before we can write the unmount record. We also so sync
         * reclaim of inodes to catch any that the above delwri flush skipped.
         */
        do {
                xfs_reclaim_inodes(mp, SYNC_WAIT);
                xfs_sync_attr(mp, SYNC_WAIT);
                pincount = xfs_flush_buftarg(mp->m_ddev_targp, 1);
                if (!pincount) {
                        delay(50);
                        count++;
                }
        } while (count < 2);
}

/*
 * 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 proceding.
 */
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);

        /* flush inodes and push all remaining buffers out to disk */
        xfs_quiesce_fs(mp);

        /*
         * 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, 1);
        if (error)
                xfs_fs_cmn_err(CE_WARN, mp,
                                "xfs_attr_quiesce: failed to log sb changes. "
                                "Frozen image may not be consistent.");
        xfs_log_unmount_write(mp);
        xfs_unmountfs_writesb(mp);
}

/*
 * Enqueue a work item to be picked up by the vfs xfssyncd thread.
 * Doing this has two advantages:
 * - It saves on stack space, which is tight in certain situations
 * - It can be used (with care) as a mechanism to avoid deadlocks.
 * Flushing while allocating in a full filesystem requires both.
 */
STATIC void
xfs_syncd_queue_work(
        struct xfs_mount *mp,
        void            *data,
        void            (*syncer)(struct xfs_mount *, void *),
        struct completion *completion)
{
        struct xfs_sync_work *work;

        work = kmem_alloc(sizeof(struct xfs_sync_work), KM_SLEEP);
        INIT_LIST_HEAD(&work->w_list);
        work->w_syncer = syncer;
        work->w_data = data;
        work->w_mount = mp;
        work->w_completion = completion;
        spin_lock(&mp->m_sync_lock);
        list_add_tail(&work->w_list, &mp->m_sync_list);
        spin_unlock(&mp->m_sync_lock);
        wake_up_process(mp->m_sync_task);
}

/*
 * 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...
 */
STATIC void
xfs_flush_inodes_work(
        struct xfs_mount *mp,
        void            *arg)
{
        struct inode    *inode = arg;
        xfs_sync_data(mp, SYNC_TRYLOCK);
        xfs_sync_data(mp, SYNC_TRYLOCK | SYNC_WAIT);
        iput(inode);
}

void
xfs_flush_inodes(
        xfs_inode_t     *ip)
{
        struct inode    *inode = VFS_I(ip);
        DECLARE_COMPLETION_ONSTACK(completion);

        igrab(inode);
        xfs_syncd_queue_work(ip->i_mount, inode, xfs_flush_inodes_work, &completion);
        wait_for_completion(&completion);
        xfs_log_force(ip->i_mount, XFS_LOG_SYNC);
}

/*
 * 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.
 */
STATIC void
xfs_sync_worker(
        struct xfs_mount *mp,
        void            *unused)
{
        int             error;

        if (!(mp->m_flags & XFS_MOUNT_RDONLY)) {
                xfs_log_force(mp, 0);
                xfs_reclaim_inodes(mp, 0);
                /* dgc: errors ignored here */
                error = xfs_qm_sync(mp, SYNC_TRYLOCK);
                if (xfs_log_need_covered(mp))
                        error = xfs_commit_dummy_trans(mp, 0);
        }
        mp->m_sync_seq++;
        wake_up(&mp->m_wait_single_sync_task);
}

STATIC int
xfssyncd(
        void                    *arg)
{
        struct xfs_mount        *mp = arg;
        long                    timeleft;
        xfs_sync_work_t         *work, *n;
        LIST_HEAD               (tmp);

        set_freezable();
        timeleft = xfs_syncd_centisecs * msecs_to_jiffies(10);
        for (;;) {
                if (list_empty(&mp->m_sync_list))
                        timeleft = schedule_timeout_interruptible(timeleft);
                /* swsusp */
                try_to_freeze();
                if (kthread_should_stop() && list_empty(&mp->m_sync_list))
                        break;

                spin_lock(&mp->m_sync_lock);
                /*
                 * We can get woken by laptop mode, to do a sync -
                 * that's the (only!) case where the list would be
                 * empty with time remaining.
                 */
                if (!timeleft || list_empty(&mp->m_sync_list)) {
                        if (!timeleft)
                                timeleft = xfs_syncd_centisecs *
                                                        msecs_to_jiffies(10);
                        INIT_LIST_HEAD(&mp->m_sync_work.w_list);
                        list_add_tail(&mp->m_sync_work.w_list,
                                        &mp->m_sync_list);
                }
                list_splice_init(&mp->m_sync_list, &tmp);
                spin_unlock(&mp->m_sync_lock);

                list_for_each_entry_safe(work, n, &tmp, w_list) {
                        (*work->w_syncer)(mp, work->w_data);
                        list_del(&work->w_list);
                        if (work == &mp->m_sync_work)
                                continue;
                        if (work->w_completion)
                                complete(work->w_completion);
                        kmem_free(work);
                }
        }

        return 0;
}

int
xfs_syncd_init(
        struct xfs_mount        *mp)
{
        mp->m_sync_work.w_syncer = xfs_sync_worker;
        mp->m_sync_work.w_mount = mp;
        mp->m_sync_work.w_completion = NULL;
        mp->m_sync_task = kthread_run(xfssyncd, mp, "xfssyncd/%s", mp->m_fsname);
        if (IS_ERR(mp->m_sync_task))
                return -PTR_ERR(mp->m_sync_task);
        return 0;
}

void
xfs_syncd_stop(
        struct xfs_mount        *mp)
{
        kthread_stop(mp->m_sync_task);
}

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);
                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));
        write_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);
        write_unlock(&pag->pag_ici_lock);
        xfs_perag_put(pag);
}

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);
        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_);
        }
}

/*
 * Inodes in different states need to be treated differently, and the return
 * value of xfs_iflush is not sufficient to get this right. The following table
 * lists the inode states and the reclaim actions necessary for non-blocking
 * reclaim:
 *
 *
 *      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, delwri ok        0               requeue
 *      dirty, delwri blocked   EAGAIN          requeue
 *      dirty, sync flush       0               reclaim
 *
 * (*) dgc: I don't think the clean, pinned state is possible but it gets
 * handled anyway given the order of checks implemented.
 *
 * As can be seen from the table, the return value of xfs_iflush() is not
 * sufficient to correctly decide the reclaim action here. The checks in
 * xfs_iflush() might look like duplicates, but they are not.
 *
 * 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. The clean inode check needs to be done before flushing
 * the inode delwri otherwise we would loop forever requeuing clean inodes as
 * we cannot tell apart a successful delwri flush and a clean inode from the
 * return value of xfs_iflush().
 *
 * Note that because the inode is flushed delayed write by background
 * writeback, 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 out delayed write inodes first before
 * trying to reclaim them to minimise the amount of time spent waiting. For
 * background relaim, we just requeue the inode for the next pass.
 *
 * Hence the order of actions after gaining the locks should be:
 *      bad             => reclaim
 *      shutdown        => unpin and reclaim
 *      pinned, delwri  => requeue
 *      pinned, sync    => unpin
 *      stale           => reclaim
 *      clean           => reclaim
 *      dirty, delwri   => flush and requeue
 *      dirty, sync     => flush, wait and reclaim
 */
STATIC int
xfs_reclaim_inode(
        struct xfs_inode        *ip,
        struct xfs_perag        *pag,
        int                     sync_mode)
{
        int     error = 0;

        /*
         * 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.
         */
        spin_lock(&ip->i_flags_lock);
        ASSERT_ALWAYS(__xfs_iflags_test(ip, XFS_IRECLAIMABLE));
        if (__xfs_iflags_test(ip, XFS_IRECLAIM)) {
                /* ignore as it is already under reclaim */
                spin_unlock(&ip->i_flags_lock);
                write_unlock(&pag->pag_ici_lock);
                return 0;
        }
        __xfs_iflags_set(ip, XFS_IRECLAIM);
        spin_unlock(&ip->i_flags_lock);
        write_unlock(&pag->pag_ici_lock);

        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);
                goto reclaim;
        }
        if (xfs_ipincount(ip)) {
                if (!(sync_mode & SYNC_WAIT)) {
                        xfs_ifunlock(ip);
                        goto out;
                }
                xfs_iunpin_wait(ip);
        }
        if (xfs_iflags_test(ip, XFS_ISTALE))
                goto reclaim;
        if (xfs_inode_clean(ip))
                goto reclaim;

        /* Now we have an inode that needs flushing */
        error = xfs_iflush(ip, sync_mode);
        if (sync_mode & SYNC_WAIT) {
                xfs_iflock(ip);
                goto reclaim;
        }

        /*
         * When we have to flush an inode but don't have SYNC_WAIT set, we
         * flush the inode out using a delwri buffer and wait for the next
         * call into reclaim to find it in a clean state instead of waiting for
         * it now. We also don't return errors here - if the error is transient
         * then the next reclaim pass will flush the inode, and if the error
         * is permanent then the next sync reclaim will reclaim the inode and
         * pass on the error.
         */
        if (error && error != EAGAIN && !XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                xfs_fs_cmn_err(CE_WARN, ip->i_mount,
                        "inode 0x%llx background reclaim flush failed with %d",
                        (long long)ip->i_ino, error);
        }
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;

reclaim:
        xfs_ifunlock(ip);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        xfs_ireclaim(ip);
        return error;

}

int
xfs_reclaim_inodes(
        xfs_mount_t     *mp,
        int             mode)
{
        return xfs_inode_ag_iterator(mp, xfs_reclaim_inode, mode,
                                        XFS_ICI_RECLAIM_TAG, 1, NULL);
}

/*
 * Shrinker infrastructure.
 */
static int
xfs_reclaim_inode_shrink(
        struct shrinker *shrink,
        int             nr_to_scan,
        gfp_t           gfp_mask)
{
        struct xfs_mount *mp;
        struct xfs_perag *pag;
        xfs_agnumber_t  ag;
        int             reclaimable;

        mp = container_of(shrink, struct xfs_mount, m_inode_shrink);
        if (nr_to_scan) {
                if (!(gfp_mask & __GFP_FS))
                        return -1;

                xfs_inode_ag_iterator(mp, xfs_reclaim_inode, 0,
                                        XFS_ICI_RECLAIM_TAG, 1, &nr_to_scan);
                /* if we don't exhaust the scan, don't bother coming back */
                if (nr_to_scan > 0)
                        return -1;
       }

        reclaimable = 0;
        ag = 0;
        while ((pag = xfs_inode_ag_iter_next_pag(mp, &ag,
                                        XFS_ICI_RECLAIM_TAG))) {
                reclaimable += pag->pag_ici_reclaimable;
                xfs_perag_put(pag);
        }
        return reclaimable;
}

void
xfs_inode_shrinker_register(
        struct xfs_mount        *mp)
{
        mp->m_inode_shrink.shrink = xfs_reclaim_inode_shrink;
        mp->m_inode_shrink.seeks = DEFAULT_SEEKS;
        register_shrinker(&mp->m_inode_shrink);
}

void
xfs_inode_shrinker_unregister(
        struct xfs_mount        *mp)
{
        unregister_shrinker(&mp->m_inode_shrink);
}