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    SubjectRe: dm: pass up rotational flag
    On Wed, May 25 2011 at  4:50pm -0400,
    Mandeep Singh Baines <msb@chromium.org> wrote:

    > Allow the NONROT flag to be passed through to linear mappings if all
    > underlying device are non-rotational. Tools like ureadahead will
    > schedule IOs differently based on the rotational flag.
    >
    > With this patch, I see boot time go from 7.75 s to 7.46 s on my device.
    >
    > Suggested-by: J. Richard Barnette <jrbarnette@chromium.org>
    > Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
    > Cc: Neil Brown <neilb@suse.de>
    > Cc: Mike Snitzer <snitzer@redhat.com>
    > Cc: Jens Axboe <jaxboe@fusionio.com>
    > Cc: Martin K. Petersen <martin.petersen@oracle.com>
    > Cc: Alasdair G Kergon <agk@redhat.com>
    > Cc: dm-devel@redhat.com

    Thanks for doing this, looks good in general.

    Just a few small nits:
    - rename device_nonrot to device_is_nonrot
    - rename dm_table_all_nonrot to dm_table_is_nonrot
    - add missing whitespace in dm_table_set_restrictions
    - move ti declaration outside of dm_table_is_nonrot's while loop
    - dm doesn't use 'true' or 'false' bool returns even though we have
    functions that return bool -- odd but best to keep consistent for now

    I'll respond with v2 that folds these changes in and my Signed-off-by
    ---
    drivers/md/dm-table.c | 18 ++++++++++--------
    1 files changed, 10 insertions(+), 8 deletions(-)

    diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
    index 40c6071..a173828 100644
    --- a/drivers/md/dm-table.c
    +++ b/drivers/md/dm-table.c
    @@ -1177,28 +1177,29 @@ static void dm_table_set_integrity(struct dm_table *t)
    blk_get_integrity(template_disk));
    }

    -static int device_nonrot(struct dm_target *ti, struct dm_dev *dev,
    - sector_t start, sector_t len, void *data)
    +static int device_is_nonrot(struct dm_target *ti, struct dm_dev *dev,
    + sector_t start, sector_t len, void *data)
    {
    struct request_queue *q = bdev_get_queue(dev->bdev);

    return q && blk_queue_nonrot(q);
    }

    -static bool dm_table_all_nonrot(struct dm_table *t)
    +static bool dm_table_is_nonrot(struct dm_table *t)
    {
    + struct dm_target *ti;
    unsigned i = 0;

    /* Ensure that all underlying device are non rotational. */
    while (i < dm_table_get_num_targets(t)) {
    - struct dm_target *ti = dm_table_get_target(t, i++);
    + ti = dm_table_get_target(t, i++);

    if (!ti->type->iterate_devices ||
    - !ti->type->iterate_devices(ti, device_nonrot, NULL))
    - return false;
    + !ti->type->iterate_devices(ti, device_is_nonrot, NULL))
    + return 0;
    }

    - return true;
    + return 1;
    }

    void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
    @@ -1213,7 +1214,8 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
    queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, q);
    else
    queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
    - if (!dm_table_all_nonrot(t))
    +
    + if (!dm_table_is_nonrot(t))
    queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
    else
    queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);

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