Recently I have seen more comments about using KWin as a stand-alone window manager in other desktop environments. It looks like quite some users are looking for a replacement for Compiz nowadays. But of course especially among the users of the lightweight desktops there is the perception that one cannot use KWin because it is done by KDE.
So I thought I spent some time on explaining about what it actually means. Of course KWin is the window manager of the KDE Plasma workspaces. And this means it is part of the KDE source code module called “kde-workspace”. Most distributions provide one package or a set of packages which depend on each other for this workspace module. This means to install KWin one has to install what people consider to be “KDE”. But it doesn’t mean that one has to run any other part of the kde-workspaces. KWin is a standalone application which only depends on the kde libraries and requires a few runtime modules (e.g. the globalshortcuts daemon or kcmshell4). One does not have to run the Plasma desktop shell or systemsettings or any other application provided by the KDE community.
So installing KWin requires to install a few more applications, but all they will do is take up some space on your hard disk. I know that people are sometimes very concerned about it, so I run “du -h” on my kde install directory. This includes not just the kde-workspace module with its dependencies, but more or less everything we have in KDE’s git repository including things like an office suite, IDE, webbrowser, artwork and many other things one doesn’t need to run a window manager 😉 The result of all that is just 13 GB of disk usage. Given current storage costs (0.06 EUR/GB) this costs less than 1 EUR which is less than a cup of coffee where I live. And remember KWin will need less storage. The bare kde-window-manager package in Debian is just around 10 MB.
I understand that people care about the dependencies and think this is important. I just don’t think it’s of any importance in a world where a movie needs significantly more data storage. Still we care about the dependencies and we are working on breaking down the dependency chain as part of the frameworks modularization efforts. One of the results of this is that we have documented dependencies nowadays. And we are working on getting the dependency to the Plasma framework as a runtime-only dependency over QtQuick, so that people can put together themeing for KWin which does not pull in any bits of the Plasma dependency. Help on that is appreciated
A more relevant issue is the question of memory usage due to running KWin. Unlike disk storage, memory storage is still rather constraint. Unfortunately it’s very difficult to provide correct measurements on the memory usage of a single KDE application. KDE applications have many shared libraries (e.g. Qt). So if KWin is the only Qt application, the relative memory usage is higher than when using several Qt applications as for example in LXDE on Qt.
Now a few highly non-scientific numbers: according to KSysGuard my self-compiled KWin (Qt4) uses around 40 MB of private memory and 38 MB of shared libraries (Qt, kdelibs, XLib, xcb, etc.). The memory usage also depends on what you use. If you activate the desktop cube effect with a 10 MB wallpaper put in the background, you will see this in the memory usage 😉 Just as another value for comparison: the iceweasel instance I’m writing this blog post in has a private memory usage of more than 700 MB. Of course KWin is with that in a different league than the minimalistic window managers, but one has to see that KWin provides more features and is a window manager and compositor. If one needs to run two applications to get close to the same feature set, it’s quite likely that the same amount of memory is needed. KWin has many features and there is no such thing as free-lunch in IT. It’s certainly possible to trim KWin down by not loading the KWin effects and ensuring that no scripts are loaded and simplified graphics.
Given that I can only recommend to give KWin a try and not to discard it because it is from KDE and might pull in some dependencies. Evaluate by the features we provide and you want to use and not by some random number on your hard disk or your memory usage.