This needs to be upvoted more. We went through similar pains when upgrading rather big app to Ruby 2.1.1 and setting RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR value to 1.3 did help reduce memory usage of Unicorn workes by almost 100MB.

I am not saying this is actual fix and I would like to hear from OP if he tried this environment variable and if it had any impact.

TL;DR New generational garbage collector of Ruby has some issues and ruby-core is working to fix it.