I'm having a strange problem with a new clean install of Ubuntu 12.10, any disk operations I do, like restoring a backup eats all my 8gb of ram, and it doesn't seen to release the memory, so I'm using swap.

It looks like a memory leak, but I don't know if I'm right.

I don't know where to begin for diagnose this things.

Details:
I don't have any applications open, except my backup being restored by ubuntu's backup application (duplicity). I'm monitoring the memory utilization by htop and free.
I know there's a lot of cached memory, but the system becomes slow and I'm using swap, so I think the kernel or whatever it is causing this problem is not freeing cache when requested.