mm: increase readahead to 512kB

According to tests, this amount of readahead is the fastest for devices with 4GB memory like ours.

Change-Id: I452bc12950de477805b49ed24fa7dd3d26bcb4ea
Signed-off-by: zwliew <zhaoweiliew@gmail.com>
sched: set sched_mc_power_savings to 2

The mc in the name of the sched_mc_power_savings parameter represents multi-core. This scheduler power saving feature corresponds to the /sys/devices/system/cpu/sched_mc_power_savings file. The default value of this parameter is 0, which does nothing. When it is set to 1, the scheduler tries to schedule processes on the least possible number of processors. In other words, the process load is distributed such that all the cores in a processor are busy before the load is distributed to the core of another processor. This saves energy by reducing the number of active processors and allowing the idle processors to go into a deeper C-state. Of course, setting it to 2 allows for more aggressive battery savings, albeit at the cost of a little more performance.

As our device is always using both cores while screen is on, this will actually help to achieve battery savings similar to hotplugging, by not using the 2nd core as much.

Change-Id: I3fcd8c5f79e81bb658fe3339b8e3611f4de634fa
Signed-off-by: zwliew <zhaoweiliew@gmail.com>