The Ruby on Rails caches_page is broken in many ways (to my believes), first of all it has a RACE bug because it does not create the cached filename atomically, and you will end up with 0 byte size cached filename. It also does not create lock files to have other process waiting instead of generating the same pages.
If you have 3 mongrel processes delivering the same non-existing (yet) page, you’ll end up with 3 mongrel processes for the same page. The following plugin does create lock files to have the 2 other waiting for a short amount of time, which should lower your cpu usage on high traffic servers.
Code is available at http://github.com/penso/caches_page_fix/