I have this problem as well on Cinnamon, so it doesn't appear to be
specific to KDE. It stalls often and frequently over 15-30 seconds at a
time for no apparent reason. But the swapping to disk may be a clue.

I see this on 5.4.0-40 and have also tried with the lowlatency version
of the kernel and it doesn't help.

One thing that seems to reduce the frequency of the problem somewhat is
to disable transparent_hugepage support but it still happens even after
that.

I have 32GB ram and it starts happening when I get to about 50% ram (mem
available) usage. The system also appears to start swapping at that
point despite what swappiness is set to. I tried setting it to 10 but it
is still swapping at what appears to be ~ 50% usage.

It appears to be very easy to reproduce if you run a few VMware VMs on a
system.

# cat /proc/sys/vm/swappiness 
10

$ free -m
              total        used        free      shared  buff/cache   available
Mem:          31030        6591         246        9050       24192       14936
Swap:         32767        4942       27825


$ cat /proc/meminfo 

MemTotal:       31774792 kB
MemFree:          256768 kB
MemAvailable:   15324804 kB
Buffers:         5887324 kB
Cached:         16712984 kB
SwapCached:       488276 kB
Active:         19816476 kB
Inactive:        8835508 kB
Active(anon):   12801324 kB
Inactive(anon):  2522936 kB
Active(file):    7015152 kB
Inactive(file):  6312572 kB
Unevictable:      145612 kB
Mlocked:              48 kB
SwapTotal:      33554428 kB
SwapFree:       28493052 kB
Dirty:           2301336 kB
Writeback:          9564 kB
AnonPages:       6161528 kB
Mapped:          7931416 kB
Shmem:           9272240 kB
KReclaimable:    2201904 kB
Slab:            2451272 kB
SReclaimable:    2201904 kB
SUnreclaim:       249368 kB
KernelStack:       21552 kB
PageTables:        85272 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    49441824 kB
Committed_AS:   30098296 kB
VmallocTotal:   34359738367 kB
VmallocUsed:       55400 kB
VmallocChunk:          0 kB
Percpu:             7712 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
ShmemPmdMapped:        0 kB
FileHugePages:         0 kB
FilePmdMapped:         0 kB
CmaTotal:              0 kB
CmaFree:               0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:               0 kB
DirectMap4k:     5078656 kB
DirectMap2M:    27346944 kB
DirectMap1G:           0 kB

** Changed in: linux (Ubuntu)
       Status: Invalid => Confirmed

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https://bugs.launchpad.net/bugs/1852001

Title:
  KDE GUI freeze on high disk IO

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  I've got massive problems with GUI on my PC.

  The attached logs are from the following setting: 
  - high disk load (f3write)
  - kernel 4.15.0-1050-oem (the only 4x kernel available in eoan)
  - no swap available

  These are the parameters (disk load, kernel, swap) I am fiddling with
  to find out the cause, see below.

  In general 
  - the problem happens once a day with any 5.0 or 5.3 kernel from eoan repo
  - more likely to happen with high disk or CPU load, but not necessarily.
  - less likely with the 4.x kernel mentioned above. 

  I just installed the following kernels from kernel-ppa:
  5.3.10-050310-generic 
  5.4.0-050400rc6-generic
  5.4.0-997-generic (drm-intel-next)
  Now I am waiting for the freeze to occur again. 

  The problem started about half a year ago. 
  There have been three changes that happened at the time and could be the cause
  - switch to kernel 5.x
  - update to Ubuntu 19.4
  - swapped motherboard, CPU and RAM. 

  The hassle started with the following scenario, repeated often: 
  - high disk load
  - PC becomes laggy
  - soon dies/freezes

  The longer I waited, the deeper the lockdown went. but I don't know the exact 
details. 
  The first cause I found was kswapd running amok and take the system with it. 
Workaround: add swap space. 

  Now the problem shifted: Whenever I got high disk load (eg dd 100 GB
  of data) the kernel swaps likle crazy and makes the GUI first lag soon
  freeze. but no excessive CPU load any more, as kswapd does not go
  crazy.

  Again I found a workaround: 
  the above mentioned 4.x kernel. In this case the GUI lags as expected from a 
heavily swapping system. nothing more. 
  but still sometimes the GUI simply freezes (the error reported at the top)

  Another workaround is to completely remove swap. Let's see what
  happens, if kswapd goes amok again.

  I am not sure as how these problems are related.

  I did extensive hardware check like
  - memtest86 newest version, no "may be vulnerable to high frequency row 
hammering"
  - smart

  do you suggest any burn in test suites?

  thanks

  ProblemType: Bug
  DistroRelease: Ubuntu 19.10
  Package: xorg 1:7.7+19ubuntu12
  ProcVersionSignature: Ubuntu 4.15.0-1050.57-oem 4.15.18
  Uname: Linux 4.15.0-1050-oem x86_64
  ApportVersion: 2.20.11-0ubuntu8.2
  Architecture: amd64
  Date: Sun Nov 10 15:55:14 2019
  DistUpgraded: 2019-10-19 13:35:30,394 DEBUG entry '# deb 
http://ppa.launchpad.net/brandonsnider/cdrtools/ubuntu cosmic main # disabled 
on upgrade to eoan' was disabled (unknown mirror)
  DistroCodename: eoan
  DistroVariant: ubuntu
  DkmsStatus:
   virtualbox, 6.0.14, 5.3.0-18-generic, x86_64: installed
   virtualbox, 6.0.14, 5.3.0-19-generic, x86_64: installed
  ExtraDebuggingInterest: Yes
  GraphicsCard:
   Intel Corporation UHD Graphics 630 (Desktop 9 Series) [8086:3e98] (prog-if 
00 [VGA controller])
     Subsystem: Micro-Star International Co., Ltd. [MSI] UHD Graphics 630 
(Desktop 9 Series) [1462:7b16]
  InstallationDate: Installed on 2017-12-16 (693 days ago)
  InstallationMedia: Kubuntu 17.10 "Artful Aardvark" - Release amd64 
(20171017.1)
  MachineType: Micro-Star International Co., Ltd. MS-7B16
  ProcEnviron:
   LANGUAGE=en_US:en
   TERM=linux
   PATH=(custom, no user)
   LANG=de_DE.UTF-8
   SHELL=/bin/bash
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-1050-oem 
root=UUID=ca93bfbd-335a-4cc7-9d0f-f0da18447497 ro quiet splash vt.handoff=7
  SourcePackage: xorg
  Symptom: display
  Title: Xorg freeze
  UpgradeStatus: Upgraded to eoan on 2019-10-19 (22 days ago)
  dmi.bios.date: 08/13/2019
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: 2.80
  dmi.board.asset.tag: Default string
  dmi.board.name: B360 GAMING PRO CARBON (MS-7B16)
  dmi.board.vendor: Micro-Star International Co., Ltd.
  dmi.board.version: 1.0
  dmi.chassis.asset.tag: Default string
  dmi.chassis.type: 3
  dmi.chassis.vendor: Micro-Star International Co., Ltd.
  dmi.chassis.version: 1.0
  dmi.modalias: 
dmi:bvnAmericanMegatrendsInc.:bvr2.80:bd08/13/2019:svnMicro-StarInternationalCo.,Ltd.:pnMS-7B16:pvr1.0:rvnMicro-StarInternationalCo.,Ltd.:rnB360GAMINGPROCARBON(MS-7B16):rvr1.0:cvnMicro-StarInternationalCo.,Ltd.:ct3:cvr1.0:
  dmi.product.family: Default string
  dmi.product.name: MS-7B16
  dmi.product.version: 1.0
  dmi.sys.vendor: Micro-Star International Co., Ltd.
  version.compiz: compiz N/A
  version.libdrm2: libdrm2 2.4.99-1ubuntu1
  version.libgl1-mesa-dri: libgl1-mesa-dri 19.2.1-1ubuntu1
  version.libgl1-mesa-glx: libgl1-mesa-glx 19.2.1-1ubuntu1
  version.xserver-xorg-core: xserver-xorg-core 2:1.20.5+git20191008-0ubuntu1
  version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
  version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:19.0.1-1ubuntu1
  version.xserver-xorg-video-intel: xserver-xorg-video-intel N/A
  version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.16-1

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