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

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Date:   Tue, 16 Feb 2021 13:36:22 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Tibor Bana <bana.tibor@...il.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>, valdis.kletnieks@...edu,
        Jan Kara <jack@...e.cz>, Pavel Machek <pavel@....cz>,
        kernel list <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...l.org>, vbabka@...e.cz,
        aarcange@...hat.com, rientjes@...gle.com, mhocko@...nel.org,
        zi.yan@...rutgers.edu, hannes@...xchg.org
Subject: Re: [regression -next0117] What is kcompactd and why is he eating
 100% of my cpu?

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.