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[Bug 1476211] Re: kswapd takes 100% CPU although there is no swap


I put 4.2.0-040200rc3-generic  under RAM stress. I still can not get to
over 5GB (of 8GB) before kswapd turns the system unusable.

** Tags added: kernel-bug-exists-upstream

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

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  kswapd takes 100% CPU although there is no swap

Status in linux package in Ubuntu:

Bug description:
  On a notebook with neither swap partition nor swap file (because of
  SSD and surplus of RAM), kswapd0 suddenly runs amok and takes 100% of
  CPU activity. When this happens, usually at most 5.5 of 8 GB RAM were
  in use, so there is no reason to swap.

  This happens so suddenly, that no user input is possible anymore, eg.
  I can barely switch to tty to kill processes that take most RAM. The
  processor becomes extremely hot and I can only turn the computer off
  and reboot. I  consider this as critical and harmful to my hardware.

  I noticed that Ubuntu installs by default with swappiness 60. Now I
  changed that to 10 because I would never encounter the case that 8GB
  are in use, but it didn't have an effect.

  Expected behavior:
  - on systems without RAM, kswapd should never attempt to swap
  - if there is not enough RAM, kernel should kill processes to free up RAM
  - no process should be able to claim so much CPU activity, that the computer becomes unresponsive (it should always be possible to control/stop/kill processes over tty)

  Actual behavior:
  - kswapd tries to swap although there is no swap space

  ProblemType: Bug
  DistroRelease: Ubuntu 15.04
  Package: linux-image-3.19.0-22-generic 3.19.0-22.22
  ProcVersionSignature: Ubuntu 3.19.0-22.22-generic 3.19.8-ckt1
  Uname: Linux 3.19.0-22-generic x86_64
  ApportVersion: 2.17.2-0ubuntu1.1
  Architecture: amd64
   /dev/snd/controlC1:  andreas    2368 F.... pulseaudio
   /dev/snd/controlC0:  andreas    2368 F.... pulseaudio
  CurrentDesktop: Unity
  Date: Mon Jul 20 12:49:24 2015
  EcryptfsInUse: Yes
  InstallationDate: Installed on 2015-06-06 (43 days ago)
  InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
  MachineType: LENOVO 20266
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.19.0-22-generic root=UUID=8a0dc2f3-fcf3-4e5b-8e23-1441bd36e3dc ro noprompt persistent quiet splash acpi_backlight=vendor vt.handoff=7 init=/sbin/upstart
   linux-restricted-modules-3.19.0-22-generic N/A
   linux-backports-modules-3.19.0-22-generic  N/A
   linux-firmware                             1.143.1
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 10/31/2013
  dmi.bios.vendor: LENOVO
  dmi.bios.version: 76CN31WW
  dmi.board.asset.tag: No Asset Tag
  dmi.board.name: Yoga2
  dmi.board.vendor: LENOVO
  dmi.board.version: 31900058STD
  dmi.chassis.asset.tag: No Asset Tag
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: Lenovo Yoga 2 Pro
  dmi.modalias: dmi:bvnLENOVO:bvr76CN31WW:bd10/31/2013:svnLENOVO:pn20266:pvrLenovoYoga2Pro:rvnLENOVO:rnYoga2:rvr31900058STD:cvnLENOVO:ct10:cvrLenovoYoga2Pro:
  dmi.product.name: 20266
  dmi.product.version: Lenovo Yoga 2 Pro
  dmi.sys.vendor: LENOVO

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