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    SubjectRe: 5.1 kernel: khugepaged stuck at 100%
    On Thu, May 09, 2019 at 05:54:56AM -0400, Justin Piszcz wrote:
    > 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?

    Could you check what khugepaged doing?

    cat /proc/$(pidof khugepaged)/stack

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