CONFIG_DM_BUFIO (not configurable)

modulename: dm-bufio.ko

configname: CONFIG_DM_BUFIO

Linux Kernel Configuration
└─>Device Drivers
└─>Multiple devices driver support (RAID and LVM)
└─>DM_BUFIO
In linux kernel since version 3.1 (release Date: 2011-10-24)  
This interface allows you to do buffered I/O on a device and acts
as a cache, holding recently-read blocks in memory and performing
delayed writes.

source code: