First of all, how are you showing the amount of RAM free? If it's via the "free" command, note that you need to be looking at the second row under "free", not the first. For example:
total used free shared buffers cached
Mem: 8191172 8059600 131572 0 169792 6648500
-/+ buffers/cache: 1241308 6949864
Swap: 0 0 0
In my case I have 8GB of RAM, but nearly 7GB of that is in buffers+cache, so my true free memory is 6.9GB, instead of the 131MB in the first column under "free".
But, as you say, 256MB of RAM isn't much. You say "it's enough for me", but if you are running out of memory with the apps running that you want, maybe you need to reconsider how much you really need.
That said, I think you probably can get your memory use more under control. First make sure you are looking at the right numbers (as mentioned above). I have a MySQL daemon running on one of my machines that gets regular but not heavy use, and it seems to be using 30MB of resident memory as shown by
ps awwlx | grep mysql. It's using another 160MB of virtual though, so it may be pretty tight.
You can try adjusting the settings in the
my.conf file to reduce the number of caches and other things, if you really want to try to shave the size of the use. Here is a good discussion of mysql memory parameters.