Re: [regression -next0117] What is kcompactd and why is he eating 100% of my cpu?

From: Jason A. Donenfeld
Date: Tue Feb 16 2021 - 07:37:16 EST


On Mon, Jan 25, 2021 at 07:54:38PM +0100, Tibor Bana wrote:
> Greetings!
>
> I don't know if it still actual, but I am strugling with this problem right now and searching the internet for solutions.
> I read the thread and saw that you are strugling to reproduce the problem, and I can reproduce it almost every day.
>
> - Install vmware player, and a linux guest.
> - Configure the virtual machine to have a good amount of memory and cpu
> - run resource intensive tasks on the guest
> - when the host used up almost it's all memory and start to reuse caches kcompactd will kick in.
>
> As I know the problem is related to transparent huge pages, but I tried to disable it.
> Today I saw the problem again and kcompactd shown an interesting status in top. It hasn't used any memory, all zeroes but it used up one core completely.
>
> My machine is a core-i7 with 4 physical cores and hyper threading and 24GB Memory
> 5.9.11-arch2-1 #1 SMP PREEMPT Sat, 28 Nov 2020 02:07:22 +0000 x86_64 GNU/Linux

Another anecdote: 5.11.0, 64 gigs of ram. If I run QEMU/KVM for a VM
with 16 gigs at the same time as a VMware VM with 16 gigs of ram,
kcompact goes wild and both VMs get really slow. The key here is running
KVM at the same time as VMware.