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[Bug 1518457] Re: kswapd0 100% CPU usage
I don't know, if the following comment be relevant to this particular bug, but here it is:
* If there is no swap, the kernel should not try to swap. As simple as this. If there is no swap file or partition, and there is kswapd0 in top, if even it doesn't consume 100% of CPU, it is a bug. Sysadmins are entitled to forbid swapping altogether (because it's evil, as on a web server swapping is effectively deny of service), and the most natural way to do so is not to mount a swap partition.
* If there is cached memory, there should be no swapping. Memory must be freed by flushing file buffers first. It is ridiculous that the kerner is generous to filesystems, caching their files, but not to the applications that really need memory, allowing either to swap or fork to fail. At the moment there is a misleading article somewhere in the Ubuntu knowledge base that claims that cached memory is not "eaten" and is as available as free. As long as the kernel is allowed to swap when there are file buffers, the latter are NOT free and available.
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kswapd0 100% CPU usage
Status in linux package in Ubuntu:
As per bug 721896 and various others:
I'm on an AWS t2.micro instance (Xeon E5-2670, 991MiB of memory).
Occasionally (about once a day), kswapd0 falls into a busy loop and
spins on 100% CPU usage indefinitely. This can be provoked by
copying/writing large files (e.g. dding a 256MB file), but it happens
occasionally otherwise. System memory usage (not including
buffers/caches) currently sits at 36%, which is typical. Initially
I had no swap space configured; I've since tried enabling a 256MB swap
file, but the problem continues to occur and no swap space is used.
The system can be recovered with `echo 1 > /proc/sys/vm/drop_caches`.
Happy to provide further information/take further debugging actions.
 Full output from `free`:
total used free shared buffers cached
Mem: 1014936 483448 531488 28556 9756 112700
-/+ buffers/cache: 360992 653944
Swap: 262140 0 262140
DistroRelease: Ubuntu 15.10
Package: linux-image-4.2.0-18-generic 4.2.0-18.22
ProcVersionSignature: Ubuntu 4.2.0-18.22-generic 4.2.3
Uname: Linux 4.2.0-18-generic x86_64
crw-rw---- 1 root audio 116, 1 Nov 19 19:40 seq
crw-rw---- 1 root audio 116, 33 Nov 19 19:40 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
Date: Fri Nov 20 20:44:30 2015
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
Lsusb: Error: command ['lsusb'] failed with exit code 1: unable to initialize libusb: -99
MachineType: Xen HVM domU
PATH=(custom, no user)
ProcFB: 0 xen
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.2.0-18-generic root=UUID=35bc01f4-4602-4823-976e-508edef899df ro console=tty1 console=ttyS0 net.ifnames=0
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.product.name: HVM domU
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