On Fri, 19 Oct 2012, Glauber Costa wrote:

We are able to match a cache allocation to a particular memcg.  If the
task doesn't change groups during the allocation itself - a rare event,
this will give us a good picture about who is the first group to touch a
cache page.

No that the infrastructure is being reworked currently which will allow
you to do this without much of a modification of individual allocators.