the X server seems like a good starting point to look at.
I'm not sure if this is sufficient info to determine which X server it is :
on puppy linux
Xorg -version
X.Org X Server 1.15.1
Release Date: 2014-04-13
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.2.0-37-generic i686 Ubuntu
Current Operating System: Linux puppypc26060 3.14.20 #1 SMP Wed Oct 22 22:28:14 BST 2014 i686
Kernel command line: initrd=initrd.gz pmedia=usbflash BOOT_IMAGE=vmlinuz
Build Date: 16 April 2014 01:40:08PM
xorg-server 2:1.15.1-0ubuntu2 (For technical support please see
http://www.ubuntu.com/support)
on puppy64 (from Xorg.0.log)
X.Org X Server 1.18.3
Release Date: 2016-04-0
[ 48.589] X Protocol Version 11, Revision 0
[ 48.589] Build Operating System: Linux 3.13.0-86-generic x86_64 Ubuntu
[ 48.589] Current Operating System: Linux puppypc22548 4.6.3 #1 SMP PREEMPT Mon Jun 27 19:59:25 BST 2016 x86_64
[ 48.589] Kernel command line: initrd=initrd.gz pmedia=usbflash BOOT_IMAGE=vmlinuz
[ 48.589] Build Date: 18 May 2016 01:07:07AM
[ 48.589] xorg-server 2:1.18.3-1ubuntu2.2 (For technical support please see
http://www.ubuntu.com/support)
on Ubuntu 10.04 (from Xorg.0.log)
X.Org X Server 1.7.6
Release Date: 2010-03-17
X Protocol Version 11, Revision 0
Build Operating System: Linux 2.6.42-37-generic i686 Ubuntu
Current Operating System: Linux computer 2.6.32-74-generic #142-Ubuntu SMP Tue Apr 28 10:02:35 UTC 2015 i686
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-2.6.32-74-generic root=UUID=e0127db5-720c-4a65-8bab-b997550cc251 ro quiet splash
Build Date: 11 April 2013 01:18:49PM
xorg-server 2:1.7.6-2ubuntu7.12 (For technical support please see
http://www.ubuntu.com/support)
This is the default X server shipped with the Ubuntu and Puppy. Is it a specific version for Ubuntu flavors of Ubuntu, or is it Xorg ?
xorg-server 2:1.15.1-0ubuntu2
xorg-server 2:1.18.3-1ubuntu2.2
grep -i video /var/log/Xorg.0.log gives nothing
grep -i memory /var/log/Xorg.0.log gives nothing
is it the Xorg shipped with Ubuntu based distributions that is flawed ( at least for the memory analysis part) ?