After installing b166f3b on Linux 4.0.0 (Ubuntu 15.04-beta2 amd64) and creating a cache with sudo flashcache_create -v -p back data /dev/disk/by-id/ata-Samsung_SSD_850_PRO_256GB_S1SUNSAG122262X-part2 /dev/disk/by-id/ata-ST1000LM014-1EJ164_W3806SK7-part4 the cache is displayed when sudo dmsetup status is invoked, but no longer after reboot (says No devices found and /dev/mapper/ doesn't contain device files, the flashcache kernel module is loaded at boot (added to /etc/modules)).