RFC Another proportional weight IO controller

Hi,

If you are not already tired of so many io controller implementations, here is another one.

This is a very eary very crude implementation to get early feedback to see if this approach makes any sense or not.

This controller is a proportional weight IO controller primarily based on/inspired by dm-ioband. One of the things I personally found little odd about dm-ioband was need of a dm-ioband device for every device we want to control. I thought that probably we can make this control per request queue and get rid of device mapper driver. This should make configuration aspect easy.

I have picked up quite some amount of code from dm-ioband especially for biocgroup implementation.

I have done very basic testing and that is running 2-3 dd commands in different cgroups on x86_64. Wanted to throw out the code early to get some feedback.

More details about the design and how to are in documentation patch.

Your comments are welcome.

Thanks
Vivek