I start out with 560 KB of free space.  I install one package and then uninstall it.  Now I have 320 KB.  What's going on here?

I've seen this happening before if you fill the overlay space. Does a reboot fix it? If not, just do a "find /overlay" to see what new files you have.

A reboot doesn't fix it.  But it does explain why when I removed non user installed package the free space decreased.

you can use "firstboot" to delete everything from /overlay and revert back to "after flash" clean situation, without no settings etc.

The rootfs is readonly u cant uninstall non user packages that will only create markers in the overlay. Read the wiki for more info

I am having the same issue.  When you installed the package, did it install any other packages as dependencies?  If it may have, try:

opkg --autoremove $package_name

I opened a bug report here after I read your post:

https://dev.openwrt.org/ticket/17803#ticket

But wont this undo everything, including things you do not want undone?

I just replicated this behavior and autoremove seemed to solve it
#900KB free space
opkg install aircrack-ng
opkg remove aircrack-ng
#500KB free space
opkg install aircrack-ng
opkg remove aircrack-ng --autoremove
#900KB free space

Problem is Ive installed and installed so many packages I can not remember.  I throughly believe there is a bug in opkg preventing the autoremove feature from operating properly, especially since the syntax Ive found on the internet, the syntax in the help file, and the syntax that actually worked for me are all different

(Last edited by cobalt60 on 10 Sep 2014, 06:21)

How can you tell what packages are user installed?

In a normal setup, files of user installed packages are in /overlay, while those in the firmware are in /rom. You need to check files from those places. E.g. /overlay/usr/sbin, /overlay/usr/bin etc.

(Last edited by hnyman on 26 Sep 2014, 06:41)