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    Subject[PATCH 27/35] nfs: livelock prevention is now done in VFS
    This reverts commit 72cb77f4a5 ("NFS: Throttle page dirtying while we're
    flushing to disk"). The two problems it tries to address

    - sync live lock
    - out of order writes

    are now all addressed in the VFS

    - PAGECACHE_TAG_TOWRITE prevents sync live lock
    - IO-less balance_dirty_pages() avoids concurrent writes

    CC: Trond Myklebust <Trond.Myklebust@netapp.com>
    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    fs/nfs/file.c | 9 ---------
    fs/nfs/write.c | 11 -----------
    include/linux/nfs_fs.h | 1 -
    3 files changed, 21 deletions(-)

    --- linux-next.orig/fs/nfs/file.c 2010-12-13 21:45:55.000000000 +0800
    +++ linux-next/fs/nfs/file.c 2010-12-13 21:46:20.000000000 +0800
    @@ -392,15 +392,6 @@ static int nfs_write_begin(struct file *
    IOMODE_RW);

    start:
    - /*
    - * Prevent starvation issues if someone is doing a consistency
    - * sync-to-disk
    - */
    - ret = wait_on_bit(&NFS_I(mapping->host)->flags, NFS_INO_FLUSHING,
    - nfs_wait_bit_killable, TASK_KILLABLE);
    - if (ret)
    - return ret;
    -
    page = grab_cache_page_write_begin(mapping, index, flags);
    if (!page)
    return -ENOMEM;
    --- linux-next.orig/fs/nfs/write.c 2010-12-13 21:45:55.000000000 +0800
    +++ linux-next/fs/nfs/write.c 2010-12-13 21:46:20.000000000 +0800
    @@ -337,26 +337,15 @@ static int nfs_writepages_callback(struc
    int nfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
    {
    struct inode *inode = mapping->host;
    - unsigned long *bitlock = &NFS_I(inode)->flags;
    struct nfs_pageio_descriptor pgio;
    int err;

    - /* Stop dirtying of new pages while we sync */
    - err = wait_on_bit_lock(bitlock, NFS_INO_FLUSHING,
    - nfs_wait_bit_killable, TASK_KILLABLE);
    - if (err)
    - goto out_err;
    -
    nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGES);

    nfs_pageio_init_write(&pgio, inode, wb_priority(wbc));
    err = write_cache_pages(mapping, wbc, nfs_writepages_callback, &pgio);
    nfs_pageio_complete(&pgio);

    - clear_bit_unlock(NFS_INO_FLUSHING, bitlock);
    - smp_mb__after_clear_bit();
    - wake_up_bit(bitlock, NFS_INO_FLUSHING);
    -
    if (err < 0)
    goto out_err;
    err = pgio.pg_error;
    --- linux-next.orig/include/linux/nfs_fs.h 2010-12-13 21:45:55.000000000 +0800
    +++ linux-next/include/linux/nfs_fs.h 2010-12-13 21:46:20.000000000 +0800
    @@ -216,7 +216,6 @@ struct nfs_inode {
    #define NFS_INO_STALE (1) /* possible stale inode */
    #define NFS_INO_ACL_LRU_SET (2) /* Inode is on the LRU list */
    #define NFS_INO_MOUNTPOINT (3) /* inode is remote mountpoint */
    -#define NFS_INO_FLUSHING (4) /* inode is flushing out data */
    #define NFS_INO_FSCACHE (5) /* inode can be cached by FS-Cache */
    #define NFS_INO_FSCACHE_LOCK (6) /* FS-Cache cookie management lock */
    #define NFS_INO_COMMIT (7) /* inode is committing unstable writes */



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