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    Subject[PATCH 06/10] readahead: remove the local copy of ra in do_generic_mapping_read()
    The local copy of ra in do_generic_mapping_read() can now go away.

    It predates readanead(req_size). In a time when the readahead code was called
    on *every* single page. Hence a local has to be made to reduce the chance of
    the readahead state being overwritten by a concurrent reader. More details in:
    Linux: Random File I/O Regressions In 2.6 <http://kerneltrap.org/node/3039>

    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
    ---
    mm/filemap.c | 20 +++++++++-----------
    1 file changed, 9 insertions(+), 11 deletions(-)

    --- linux-2.6.22-rc6-mm1.orig/mm/filemap.c
    +++ linux-2.6.22-rc6-mm1/mm/filemap.c
    @@ -863,7 +863,7 @@ static void shrink_readahead_size_eio(st
    * It may be NULL.
    */
    void do_generic_mapping_read(struct address_space *mapping,
    - struct file_ra_state *_ra,
    + struct file_ra_state *ra,
    struct file *filp,
    loff_t *ppos,
    read_descriptor_t *desc,
    @@ -877,12 +877,11 @@ void do_generic_mapping_read(struct addr
    unsigned long prev_index;
    unsigned int prev_offset;
    int error;
    - struct file_ra_state ra = *_ra;

    index = *ppos >> PAGE_CACHE_SHIFT;
    next_index = index;
    - prev_index = ra.prev_pos >> PAGE_CACHE_SHIFT;
    - prev_offset = ra.prev_pos & (PAGE_CACHE_SIZE-1);
    + prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
    + prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
    last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
    offset = *ppos & ~PAGE_CACHE_MASK;

    @@ -897,7 +896,7 @@ find_page:
    page = find_get_page(mapping, index);
    if (!page) {
    page_cache_sync_readahead(mapping,
    - &ra, filp,
    + ra, filp,
    index, last_index - index);
    page = find_get_page(mapping, index);
    if (unlikely(page == NULL))
    @@ -905,7 +904,7 @@ find_page:
    }
    if (PageReadahead(page)) {
    page_cache_async_readahead(mapping,
    - &ra, filp, page,
    + ra, filp, page,
    index, last_index - index);
    }
    if (!PageUptodate(page))
    @@ -1016,7 +1015,7 @@ readpage:
    }
    unlock_page(page);
    error = -EIO;
    - shrink_readahead_size_eio(filp, &ra);
    + shrink_readahead_size_eio(filp, ra);
    goto readpage_error;
    }
    unlock_page(page);
    @@ -1053,10 +1052,9 @@ no_cached_page:
    }

    out:
    - *_ra = ra;
    - _ra->prev_pos = prev_index;
    - _ra->prev_pos <<= PAGE_CACHE_SHIFT;
    - _ra->prev_pos |= prev_offset;
    + ra->prev_pos = prev_index;
    + ra->prev_pos <<= PAGE_CACHE_SHIFT;
    + ra->prev_pos |= prev_offset;

    *ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
    if (filp)
    --
    -
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