I'm not sure this is the right forum, but anyway.

I have recently switched from fancy KDE app launcher to more traditional menu-based. I have also switched from Pidgin to Kopete. The system became very slow to switch between windows, to display menus, to show my auto-hiding panels etc. It easily took up to five seconds to show Kopete's menu on the tray icon. At first i thought it's Nepomuk, or Akonadi, or whatever else i turned on along the way, but after i switched back to fancy KDE menu and turned off Kopete, Plasma is fast again.

Moreover, when i change to classic menu again and turn on Kopete - the system stays responsive for a while, but then after some time it becomes sluggish again.

What could be the problem here?

Can you try using Kopete with the Fancy menu and the classic menu without Kopete and see if you have the same responsiveness issues?

I suspect that Classic menu may be sending D-Bus commands to Kopete and it's responses are lagging.

Turns out it's not KDE's fault after all. I remember when everything became slow, Xorg was consuming ~300Mb RAM. I was finally fed up with it, logged out and restarted X through KDM. After login, X was consuming only 40-50 Mb RAM. I was keeping eye on RAM usage and it was pretty normal right up until i sent my machine to standby. When i turned it on, it went back up and is currently ~200Mb (i suspect it goes up every standby, and as i tend to do these a lot, it sorta keeps growing until system becomes barely useable).

So it appears to be an X or Nvidia bug related to standby. I will test this with nouveau.

Nouveau doesn't seem to have that problem, although i'm not 100% sure as nouveau locks up my GPU pretty quickly (~3-5 minutes) and i have to restart X. So it's either a problem with Xorg or with Nvidia driver.

Ok, not much you can do in this case other than hope that an update to X/NVidia fixes it, or an unrelated change in KDE which manages to not trigger the bug.

I am now running nouveau (with noaccel as otherwise it locks up within minutes from boot) and Xorg eats 200Mb RAM and everything is as snappy as ever.

So maybe nvidia driver bug, or obscure KDE/X bug that is not really related to memory consumption...