Why put just one dir on your lvm partition?
I suggest putting following on it:
You can even put your swap onto it. (I did
Putting your / onto it is not recommended. But if you really want to, read this:
First you have to make sure that lvm-support is compiled into your kernel.
don't forget to install the lvm-user package
then as you said:
make your lvm-partition
mke2fs -j /dev/lvmpart/usr
making it larger:
# lvextend -L+1G /dev/lvmpart/usr (change this as neccecary)
# resize2fs -f /dev/lvmpart/usr (i'm using reiserfs and have to use resize_reiserfs)
you don't even have to unmount it!
I don't use LVM very long, but I think its great. I have a normal partition and a second harddrive that form the lvm-partition and had to extend and shrink a few things already. Everyone should use it.