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    Subject[patch 83/94] nfs: remove redundant tests on reading new pages
    2.6.28-stable review patch.  If anyone has any objections, please let us know.


    From: Wu Fengguang <>

    commit 136221fc3219b3805c48db5da065e8e3467175d4 upstream.

    aops->readpages() and its NFS helper readpage_async_filler() will only
    be called to do readahead I/O for newly allocated pages. So it's not
    necessary to test for the always 0 dirty/uptodate page flags.

    The removal of nfs_wb_page() call also fixes a readahead bug: the NFS
    readahead has been synchronous since 2.6.23, because that call will
    clear PG_readahead, which is the reminder for asynchronous readahead.

    More background: the PG_readahead page flag is shared with PG_reclaim,
    one for read path and the other for write path. clear_page_dirty_for_io()
    unconditionally clears PG_readahead to prevent possible readahead residuals,
    assuming itself to be always called in the write path. However, NFS is one
    and the only exception in that it _always_ calls clear_page_dirty_for_io()
    in the read path, i.e. for readpages()/readpage().

    Cc: Trond Myklebust <>
    Signed-off-by: Wu Fengguang <>
    Signed-off-by: Trond Myklebust <>
    Signed-off-by: Greg Kroah-Hartman <>

    fs/nfs/read.c | 6 ------
    1 file changed, 6 deletions(-)

    --- a/fs/nfs/read.c
    +++ b/fs/nfs/read.c
    @@ -533,12 +533,6 @@ readpage_async_filler(void *data, struct
    unsigned int len;
    int error;

    - error = nfs_wb_page(inode, page);
    - if (error)
    - goto out_unlock;
    - if (PageUptodate(page))
    - goto out_unlock;
    len = nfs_page_length(page);
    if (len == 0)
    return nfs_return_empty_page(page);

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