Cannot run btrfs defragment when using kernel 3.14.x, updating to latest git version (v3.14) resolved the issue. Need to add newer version of btrfs-progs.
*btrfs-progs-3.14_pre20140414 (14 Apr 2014) 14 Apr 2014; Sergei Trofimovich <slyfox@gentoo.org> +btrfs-progs-3.14_pre20140414.ebuild: Bump snapshot up to latest stable upstream tag v3.14 (bug #507008 by Duncan). Assumed fixed.