mm: readahead to 512
deadline: Allow 0ms deadline latency, increase the read speed

Change a timer compare from after to after-equals, thus allowing
0 timeout and making deadline schedule FIFO.

Signed-off-by: xiaobing tu <xiaobing.tu@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: flar2 <asegaert@gmail.com>

Conflicts:
	block/deadline-iosched.c

Conflicts:
	block/deadline-iosched.c