Comment 1 for bug 135166

Thank you for trying to help make Ubuntu better. However this seems to be normal (and desirable) behaviour. The general principle is: if RAM isn't used, it's wasted.

The "cache" entry in your free -m results indicates that the kernel currently has a 1.4Gb disc cache. This memory is free for application use - if an application requests more RAM, some of that disc cache will be dropped. The second entry in your +/- buffers/cache indicates that, as far as applications are concerned, you have 1796 Mb of RAM free.

You can see «http://gentoo-wiki.com/FAQ_Linux_Memory_Management» for more details about how the linux kernel manages memory.