- I have tested a fresh installation (via usb-stick) of Kubuntu 12.04.x with nvidia driver 331.113-0ubuntu0.0.0.3 and 304.125-0ubuntu0.0.0.1 , but I cannot reproduce the problem there (a few hours of testing).

But with a fresh user on the affected installation, the memory leak occurs.

- On my Office PC (12.04.x) with nvs300 the problem is gone, but I don't know why. (nvidia driver 304.125-0ubuntu0.0.0.1)
There was a kernel update linux-image-3.2.0-75-generic, but I don't know if this is connected. I installed and reinstalled several times different kernels.
changelog
linux (3.2.0-75.110) precise; urgency=low

[ Kamal Mostafa ]

* Release Tracking Bug
- LP: #1403154

[ Upstream Kernel Changes ]

* kvm: fix excessive pages un-pinning in kvm_iommu_map error path.
- LP: #1386395
- CVE-2014-8369
* KVM: x86: Don't report guest userspace emulation error to userspace
- LP: #1392823
- CVE-2014-7842
* drivers:scsi:storvsc: Fix a bug in handling ring buffer failures that
may result in I/O freeze
- LP: #1400289
* net:socket: set msg_namelen to 0 if msg_name is passed as NULL in
msghdr struct from userland.
- LP: #1335478

-- Kamal Mostafa <email address hidden> Tue, 16 Dec 2014 10:00:12 -0800

- On my Home PC (GT 430) the problem is still there;

That's why I have upgraded to the latest Ubuntu LTS version 14.04.x
There I installed the Utopic(14.10) kernel (3.16) with the Utopic xstack (Xserver 1.16.x) with latest nvidia 346.35 driver (with the default settings), but still the problem, but now with a crash after growing of kwin and xorg.

Memory consumption after ~ 16 hours of normal working, then after 30 min after the xrestop measurement => crash and restart of the xserver (log attached)
(Full HD resolution with KDE-effects enabled (on the office pc I have exactly the same effects with the same settings)).
kwin:
Memory: 218,3 MiB
Shared: 98,5 MiB

Xorg
Memory: 217,2 MiB
Shared: 78,7 MiB

plasma-desktop
Memory: 125,4 MiB
Shared: 91,6 MiB

xrestop - Display: localhost
Monitoring 44 clients. XErrors: 0
Pixmaps: 209917K total, Other: 152K total, All: 210070K total

res-base Wins GCs Fnts Pxms Misc Pxm mem Other Total PID Identifier
2000000 84 14 0 1593 1903 142735K 46K 142782K 2732 kwin

[ 6422.217] (EE) Backtrace:
[ 6422.221] (EE) 0: /usr/bin/X (xorg_backtrace+0x48) [0x7f7dcd5bde88]
[ 6422.221] (EE) 1: /usr/bin/X (0x7f7dcd419000+0x1a8ea9) [0x7f7dcd5c1ea9]
[ 6422.221] (EE) 2: /lib/x86_64-linux-gnu/libc.so.6 (0x7f7dcb599000+0x36d40) [0x7f7dcb5cfd40]
[ 6422.221] (EE) 3: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x5a1d96) [0x7f7dc582ad96]
[ 6422.221] (EE) 4: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x57fb79) [0x7f7dc5808b79]
[ 6422.221] (EE) 5: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x134922) [0x7f7dc53bd922]
[ 6422.221] (EE) 6: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x1388f7) [0x7f7dc53c18f7]
[ 6422.221] (EE) 7: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x136e29) [0x7f7dc53bfe29]
[ 6422.221] (EE) 8: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x12f4b2) [0x7f7dc53b84b2]
[ 6422.221] (EE) 9: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x1376e9) [0x7f7dc53c06e9]
[ 6422.221] (EE) 10: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x13a3bb) [0x7f7dc53c33bb]
[ 6422.221] (EE) 11: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x112722) [0x7f7dc539b722]
[ 6422.221] (EE) 12: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so (0x7f7dc5289000+0x5705a3) [0x7f7dc57f95a3]
[ 6422.221] (EE) 13: /usr/lib/x86_64-linux-gnu/xorg/extra-modules/libglx.so (0x7f7dc8c26000+0x6ed9fb) [0x7f7dc93139fb]
[ 6422.221] (EE)
[ 6422.221] (EE) Segmentation fault at address 0x0
[ 6422.221] (EE)
Fatal server error:
[ 6422.221] (EE) Caught signal 11 (Segmentation fault). Server aborting