I have just upgraded from kubuntu 14.04 to 15.04, but I didn't really expect to find so much less than before on an upgrade, but what it's really disappointing me is how plasma 5 is using memory. KDE 4.14 was using no more than 0.9 GB memory whereas KDE 5 has doubled its needs (around 1,8 GB). These measures have been taken on startup. This is disastrous on a 4GB setup because there is not much left for applications, and if I open something the amount of memory used increases and won't come back!
Just to name something is behaving differently: plasma-desktop was using 130MB before the upgrade, while now is above 220MB.
If there is not a solution to this, apart from buying new RAM, please tell me how to install KDE4 on kubuntu 15.04. Thanks

I can confirm this:

Hi,

I have Kubuntu 15.04 since the beta installed, and I can confirm it is a memory hog. I realized it must be because by default Kubuntu comes with a lot of apps I never use, and alot of these apps are started at runtime, consuming memory while not being useful to me. Right after boot, memory usage is at ~1.3 GB. I deinstalled a few apps, those that seemed "save" to remove to me (I'm just getting started with Linux so i'm usually careful to not break things). But it didn't get much better, really.

Now I have installed Arch Linux over the weekend, which comes with the premise that you have to setup the distro how you like it. I really like the concept so i gave it a try, and it wasn't that hard to install (I'm a year long windows user). I installed Plasma 5, which by itself comes with nothing but the Plasma shell and a few widgets! No other KDE apps come by default. I could cherry pick the KDE apps I like and use, and install lightweight alternatives for everything else I need.

The plasmashell process itself still consumes around ~200 MB, but if you install just the Plasma 5 package from Arch the whole desktop will consume around ~800 MB after boot. I am now at with all my apps at ~900 MB after startup, which is still very nice. I can't help but Plasma on Arch also feels snappier than on Kubuntu (I'm using both, booting both and forth).

And so far I really like the Plasma 5 desktop (never used KDE 4 though!), it totally makes me want to ask my boss to let me use Linux instead of Windows at work

The "virtual size" just says how much memory is blended into the process, it has no meaning regarding the actual physical RAM usage (ie. if you eg. mmap a 4GB file into the process to access random parts of it, the virtual memory will raise by 4GB while the actual memory consumption is virtually unchanged)

The screenshow shows plasmashell to use ~300MB ram, ~90 of them are shared w/ other processes ie. killing plasmashell would free ~209MB

Here is the memory consumption of my Plasma 5 dekstop on my Arch installation right after boot:

http://i.imgur.com/gwZgRK9.jpg

As you can see, you see nothing Not many background apps running, consuming only ~0.6 GB in total. Yesterday I wrote 0.8 GB, but that was off the top of my head and now I was curious and wanted to verify that before leaving back to the Windows world at work

I use Chromium to browse the web, Spotify to hear music and Sublime Text to edit my code. Here is a screenshot with those apps running, I opened them right after boot. Chromium has 11 tabs open:

http://i.imgur.com/fqUJJzw.png

Now it's at 1.7 GB, and that's not bad at all in my opinion. Granted, plasmashell will grow to up to ~210 MB after some time, but nothing that will slow down my computer. I will do the same "test" next time with Kubuntu.

I'm also experimenting with the linux-ck kernels, from the arch user repos. It has the BFS and BFQ schedulers patched in. I didn't any load tests yet, but I have noticed that BFQ has improved responsiveness during file I/O, which is really awesome, I had no noticeable app freezes yet. I'll try to come up with some tests at some point in the future, comparing the stock kernel with the patched running Plasma 5, doing some real world load tests. I'm really curious to see how they compare.