devfs is a virtual file system. You can't add more space to it - it will always take as much space as is required.
Generally, anything that doesn't have a path starting with /dev as the second field of the fstab or output of "mount" is a special file system.
Oh, and general good principle to operate by - if it isn't broken, don't fix it (also known as, if you don't have a problem, don't go looking to create one unless you know what you're doing).