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    Subject[PATCH] nfs: remove redundant tests on reading new pages
    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 <Trond.Myklebust@netapp.com>
    Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
    ---
    fs/nfs/read.c | 6 ------
    1 file changed, 6 deletions(-)

    This bug was found when playing with my readahead tracing module posted at
    http://lkml.org/lkml/2008/11/27/373 and confirmed to work.

    The NFS readahead traces are now

    [ 59.972526] readahead-initial0(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=0+25, ra=0+60-30, async=0) = 60
    [ 59.992734] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=30+20, ra=60+30-30, async=1) = 30
    [ 60.030900] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=60+15, ra=90+30-30, async=1) = 30
    [ 60.031687] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=90+10, ra=120+30-30, async=1) = 30

    The async field was always 0 before this patch.

    --- linux-2.6.orig/fs/nfs/read.c
    +++ linux-2.6/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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