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

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Message-ID: <178586.1611651136@turing-police>
Date:   Tue, 26 Jan 2021 03:52:16 -0500
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Tibor Bana <bana.tibor@...il.com>
cc:     Mel Gorman <mgorman@...hsingularity.net>, 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, 25 Jan 2021 19:54:38 +0100, Tibor Bana said:

> 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.

I'm pretty sure that you have a real bug on your hands.  Even if your box
is very low on memory, kcompactd should eventually figure out it's not
making any progress and wait for the situation to change before trying again.

However, I'm also pretty sure that it's a different one than the one we were
chasing, because that one never showed up again once all the patches landed in
linux-next, some 18 months before 5.9 was released.