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

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Date:   Sun, 27 Jan 2019 17:00:27 +0100
From:   Pavel Machek <pavel@....cz>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     valdis.kletnieks@...edu,
        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, jack@...e.cz
Subject: Re: [regression -next0117] What is kcompactd and why is he eating
 100% of my cpu?

Hi!

> > > top - 13:38:51 up  1:42, 16 users,  load average: 1.41, 1.93, 1.62
> > > Tasks: 182 total,   3 running, 138 sleeping,   0 stopped,   0 zombie
> > > %Cpu(s):  2.3 us, 57.8 sy,  0.0 ni, 39.9 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
> > > KiB Mem:   3020044 total,  2429420 used,   590624 free,    27468 buffers
> > > KiB Swap:  2097148 total,        0 used,  2097148 free.  1924268 cached Mem
> > >
> > >   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
> > >   608 root      20   0       0      0      0 R  99.6  0.0  11:34.38 kcompactd0
> > >  9782 root      20   0       0      0      0 I   7.9  0.0   0:59.02 kworker/0:
> > >  2971 root      20   0   46624  23076  13576 S   4.3  0.8   2:50.22 Xorg
> > 
> > I've noticed this as well on earlier kernels (next-20181224 to 20190115)
> > 
> > Some more info:
> > 
> > 1) echo 3 > /proc/sys/vm/drop_caches  unwedges kcompactd in 1-3 seconds.
> > 
> 
> This aspect is curious as it indicates that kcompactd could potentially
> be infinite looping but it's not something I've experienced myself. By
> any chance is there a preditable reproduction case for this?

I seen it exactly once, so not sure how reproducible this is. x86-32
machine, running chromium browser, so yes, there was some swapping
involved.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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