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

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Date:   Wed, 27 Jan 2021 20:29:43 +0100
From:   Tibor Bana <bana.tibor@...il.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     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?

Hi,
Sorry for the delay. I had time to do a full system upgrade yesterday
evening and fortunately Archlinux already ships 5.10.10, today I used
my computer as usual to test it. I haven't experienced the symptoms,
but since I disabled transparent huge pages it showed up sporadically.
If I face it again I will let you know.

On Tue, Jan 26, 2021 at 10:17 AM Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> 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
> >
> > Hope this can help, to point out the problem.
> >
>
> Is 5.10.10 affected because it included two patches related to halting
> compaction that are relevant.
>
> d20bdd571ee5c9966191568527ecdb1bd4b52368 mm/compaction: stop isolation if too many pages are isolated and we have pages to migrate
> 38935861d85a4d9a353d1dd5a156c97700e2765d mm/compaction: count pages and stop correctly during page isolation
>
> --
> Mel Gorman
> SUSE Labs