5.1 kernel: khugepaged stuck at 100%

["Justin Piszcz" <jpiszcz@lucidpixels.com>]

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Hello,

Kernel: 5.1 (self-compiled, no modules)
Arch: x86_64
Distro: Debian Testing

Issue: I was performing a dump of ext3 and ext4 filesystems and then
restoring them to a separate volume (testing)-- afterwards I noticed that
khugepaged is stuck at 100% CPU. It is currently still stuck at 100% CPU, is
there anything I can do to debug what is happening prior to a reboot to work
around the issue?  I have never seen this behavior prior to 5.1. 

$ cat /proc/cmdline
auto BOOT_IMAGE=5.1.0-2 ro root=901 3w-sas.use_msi=1 nohugeiomap
page_poison=1 pcie_aspm=off pti=on rootfstype=ext4 slub_debug=P
zram.enabled=1 zram.num_devices=12 zswap.enabled=1 zswap.compressor=lz4
zswap.zpool=z3fold

$ 5.1 .config attached: config.txt.gz

$ attachment: graphic.JPG -> graph of the processes, dark green ->
khugepaged

$ top

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   77 root      39  19       0      0      0 R 100.0   0.0  23:29.27
khugepaged
    1 root      20   0  171800   7832   4948 S   0.0   0.0   1:25.59 systemd
    2 root      20   0       0      0      0 S   0.0   0.0   0:00.02
kthreadd
    3 root       0 -20       0      0      0 I   0.0   0.0   0:00.00 rcu_gp
    4 root       0 -20       0      0      0 I   0.0   0.0   0:00.00
rcu_par_gp
    6 root       0 -20       0      0      0 I   0.0   0.0   0:00.00
kworker/0+
    8 root       0 -20       0      0      0 I   0.0   0.0   0:00.00
mm_percpu+

Thoughts on debugging / before reboot to clear this up?

Thanks,

Justin.

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