On Mon, Jan 21, 2013 at 08:09:51AM -0500, Mike Snitzer wrote:

dm-cache is under active review for upstream inclusion.  I wouldn't
categorize the chances of dm-cache going upstream when the v3.9 merge
window opens as "very low".  But even if dm-cache does go upstream it
doesn't preclude bcache and/or enhanceio from going upstream too.

As I understand it bcache is being reviewed too.