ublk: cache-align struct ublk_io

ublk: cache-align struct ublk_io

struct ublk_io is already 56 bytes on 64-bit architectures, so round it
up to a full cache line (typically 64 bytes). This ensures a single
ublk_io doesn't span multiple cache lines and prevents false sharing if
consecutive ublk_io's are accessed by different daemon tasks.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250620151008.3976463-15-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>