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Bug 1694305 - kcompacd0 using 100% cpu
Summary: kcompacd0 using 100% cpu
Status: NEW
Alias: None
Product: Fedora
Classification: Fedora
Component: kernel
Version: 29
Hardware: x86_64
OS: Linux
Target Milestone: ---
Assignee: Kernel Maintainer List
QA Contact: Fedora Extras Quality Assurance
Depends On:
TreeView+ depends on / blocked
Reported: 2019-03-30 10:37 UTC by Fredrik Mikker
Modified: 2019-04-01 22:23 UTC (History)
16 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Last Closed:

Attachments (Terms of Use)
kernel log (deleted)
2019-03-30 10:37 UTC, Fredrik Mikker
no flags Details
trace.dat.gz (deleted)
2019-03-30 10:39 UTC, Fredrik Mikker
no flags Details
transparent_hugepage (deleted)
2019-03-30 10:43 UTC, Fredrik Mikker
no flags Details
kcompatd-trace (deleted)
2019-04-01 22:23 UTC, Fredrik Mikker
no flags Details

Description Fredrik Mikker 2019-03-30 10:37:08 UTC
Created attachment 1549716 [details]
kernel log

1. Please describe the problem:

The process kcompactd0 is using 100% cpu on one core during performance demanding tasks.
In my case this is happening when I'm running applications using much resources in a virtual machine.

2. What is the Version-Release number of the kernel:


3. Did it work previously in Fedora? If so, what kernel version did the issue
   *first* appear?  Old kernels are available for download at :

The issue started after upgrading to the 5.0.4 kernel. The issue was not present in kernel-core-4.20.14-200

4. Can you reproduce this issue? If so, please provide the steps to reproduce
   the issue below:


1. Run performance demanding tasks such as running virtual machines, compiling a large source tree or similar.

5. Does this problem occur with the latest Rawhide kernel? To install the
   Rawhide kernel, run ``sudo dnf install fedora-repos-rawhide`` followed by
   ``sudo dnf update --enablerepo=rawhide kernel``:

6. Are you running any modules that not shipped with directly Fedora's kernel?:

Yes. zfs and Nvidia

7. Please attach the kernel logs. You can get the complete kernel log
   for a boot with ``journalctl --no-hostname -k > dmesg.txt``. If the
   issue occurred on a previous boot, use the journalctl ``-b`` flag.

The issue is known upstream and is discussed in the following LKML-thread:

A workaround is to drop the caches which mitigates the issue for a short while:

# echo 3 > /proc/sys/vm/drop_caches

Comment 1 Fredrik Mikker 2019-03-30 10:39:40 UTC
Created attachment 1549717 [details]

A trace while kcompactd is pegged at 100% is attached, and created by using the following command:

# trace-cmd record -a -e compaction -e migrate -e kmem:mm_page_alloc -e vmscan:mm_vmscan_kswapd_wake -e vmscan:mm_vmscan_kswapd_sleep sleep 10

Comment 2 Fredrik Mikker 2019-03-30 10:43:08 UTC
Created attachment 1549718 [details]

As requested upstream[1] the output from # grep -r . /sys/kernel/mm/transparent_hugepage/* is attached.


Comment 3 Fredrik Mikker 2019-04-01 22:23:45 UTC
Created attachment 1550794 [details]

Another datapoint requested from upstream dev.

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