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    Subject[RFC 17/23] readahead: set the minimum ra size in get_(init|next)_ra
    Date
    From: Luis Chamberlain <mcgrof@kernel.org>

    Make sure the minimum ra size is based on mapping_min_order in
    get_init_ra() and get_next_ra(). If request ra size is greater than
    mapping_min_order of pages, align it to mapping_min_order of pages.

    Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
    ---
    mm/readahead.c | 26 ++++++++++++++++++++++++--
    1 file changed, 24 insertions(+), 2 deletions(-)

    diff --git a/mm/readahead.c b/mm/readahead.c
    index fb5ff180c39e..7c2660815a01 100644
    --- a/mm/readahead.c
    +++ b/mm/readahead.c
    @@ -357,9 +357,17 @@ void force_page_cache_ra(struct readahead_control *ractl,
    * for small size, x 4 for medium, and x 2 for large
    * for 128k (32 page) max ra
    * 1-2 page = 16k, 3-4 page 32k, 5-8 page = 64k, > 8 page = 128k initial
    + *
    + * For higher order address space requirements we ensure no initial reads
    + * are ever less than the min number of pages required.
    + *
    + * We *always* cap the max io size allowed by the device.
    */
    -static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
    +static unsigned long get_init_ra_size(unsigned long size,
    + unsigned int min_order,
    + unsigned long max)
    {
    + unsigned int min_nrpages = 1UL << min_order;
    unsigned long newsize = roundup_pow_of_two(size);

    if (newsize <= max / 32)
    @@ -369,6 +377,15 @@ static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
    else
    newsize = max;

    + if (newsize < min_nrpages) {
    + if (min_nrpages <= max)
    + newsize = min_nrpages;
    + else
    + newsize = round_up(max, min_nrpages);
    + }
    +
    + VM_BUG_ON(newsize & (min_nrpages - 1));
    +
    return newsize;
    }

    @@ -377,14 +394,19 @@ static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
    * return it as the new window size.
    */
    static unsigned long get_next_ra_size(struct file_ra_state *ra,
    + unsigned int min_order,
    unsigned long max)
    {
    - unsigned long cur = ra->size;
    + unsigned int min_nrpages = 1UL << min_order;
    + unsigned long cur = max(ra->size, min_nrpages);
    +
    + cur = round_down(cur, min_nrpages);

    if (cur < max / 16)
    return 4 * cur;
    if (cur <= max / 2)
    return 2 * cur;
    +
    return max;
    }

    --
    2.40.1
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