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Ubuntu 18.04, Xorg and system-journald consuming CPU
After an update of ubuntu at two weeks ago, Xorg started consuming the CPU excessively:
command top output

Tarefas: 312 total,   2 executando, 247 dormindo,   0 parado,   0 zumbi
%Cpu(s): 23,7 us, 48,0 sy,  0,0 ni, 27,4 id,  0,8 wa,  0,0 hi,  0,1 si,  0,0 st
KiB Mem : 16321780 total, 12180560 free,  1869344 used,  2271876 buff/cache
KiB Swap:  7813116 total,  7813116 free,        0 used. 14068084 avail Mem

 PID USUÁRIO  PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
1418 gdm       20   0  292704  63940  33468 S 131,1  0,4   2:31.88 Xorg
 315 root      19  -1  119924  31060  29872 R  96,0  0,2   1:49.05 systemd-journal
1194 syslog    20   0  263036   5276   3600 S  52,3  0,0   1:04.29 rsyslogd 

In 30 minuts, the systemd-journal consumes more than 10Gb of HD. I've been researching but I have not found much. What I have done is open T:

$ sudo systemctl stop systemd-journald
$ sudo killall Xorg

After that again, I type:

$ sudo systemctl restart systemd-journald  

But sometimes it the screen locks and I can not log in anymore, just turn off the notebook directly on the button.
I have already looked at several logs and did not find much useful information. The specifications of my hardware and software are:

Notebook Dell Intel® Core™ i7-7500U CPU @ 2.70GHz × 4
RAM 16Gb
Graphics NVIDIA® GeForce® 940MX de 4GB, GDDR5​
Linux Ubuntu 18.04
Graphic driver nvidia-driver-396

Over the past two weeks I've been waiting for some update, but it not happen. Thanks for any help.

I don't know if it makes difference, but I install kernel 4.17 using ukuu.
And so, I found the following information on syslog in so many lines:

SynPS/2 Synaptics TouchPad: Read error 9

I did remove xserver-xorg-input-synaptics and Xorg stopped consuming cpu and HD, but now gnome-shell is in 100% now.

So, what are the errors reported by systemd-journald ? Please update your question with this info.

This is a Q&A site - we expect questions and answers. It is ok to answer your own question. So please move the solution to anew answer.

OP’s own answer moved here from the question body:

I was using gdm3 as login manager. I switched to LightDM and the gnome stopped consuming 100% of the CPU.
sudo dpkg-reconfigure gdm3



This worked for me! Just remember to reboot after reconfiguring to LightDm

Temporary solution
I do not know why, but it's working as a temporary solution. After logging into the machine, I kill the gnome-shell process on a terminal, started as root by gdm, and start it as a normal user. It stops using too much cpu.

$ sudo killall gnome-shell
$ gnome-shell &

