Published Aug 09, 2022
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Kernel modules are object files that contain code to extend the kernel of an operating system. Kernel modules are used to add support for new hardware and/or filesystems, or for adding system calls. Modules can be built into the kernel or compiled as loadable kernel modules.
Most modern Gentoo installations will use a device manager, such as udev, to
automatically load and manage kernel modules, thus module loading will often
need no particular configuration.
Many Loadable kernel modules (LKMs) may also be compiled “in-kernel”. See configuring a kernel on how to select either built-in and LKM options.
Using LKMs can result in a smaller kernel memory footprint, by not having unneeded modules loaded: modules can be loaded on demand by udev (for example DVB drivers for a DVB stick). Compile-in-kernel code will not be able to be reloaded while the kernel is running, but LKMs can sometimes be used to solve certain issues, by unloading and reloading them.
Using a module rather than building code into the kernel also permits the
setting of module-specific parameters, through the /etc/modprobe.d file - see
man /etc/modprobe.d.
Modules needed early in the boot process may require an update of the initramfs after a kernel update or recompilation (e.g. filesystem drivers for filesystems used for boot). Some LKMs may incur a slight performance penalty over built-in code, due to the addition of an API layer and slightly more memory usage.
Beware of file system module X located on a partition formatted with X (unbootable system at worst).