mmap performance of Amazon ESB

I am looking at porting an application to the cloud, more speficially I am looking at Amazon EC2 or Google GCE.

My app heavily uses Linux's mmap to memory map large read-only files and I I would like to understand how mmap would actually work when a file is on the ESB volume.

I would specifically like to know what happens when I call mmap as EBS appears to be a black-box. Also, are the benefits negated?