seek_mean could be very big sometimes, using it as close criteria is meaningless
as this doen't improve any performance. So if it's big, let's fallback to
default value.
Reviewed-by: NCorrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Shaohua Li<shaohua.li@intel.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>