Funtoo's lvm2 ebuild outdated and missing some upstream changes. Following changes added in newer ebuild:
1. support for thinly-provisioned lvm
https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/thinprovisioned_volumes.html
`thin` USE flag is not enabled by default, building lvm2 with thin-provisioning require boost.
2. support for lvm2 volatile data in /run
3. this ebuild has upstream init scripts
4. lvm and device-mapper automatically installed in boot runlevel as required for genkernel
Works fine, installed debian-sources without problem, full reinstall with LVM partitioning on the way.