Discussion:
CPU hog in vnlru and arc_prune on 13-STABLE
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Juraj Lutter
2024-03-01 19:19:57 UTC
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Hi,

I have a fresh (git b9880e247b26) 13.3-STABLE running in bhyve with 2 vCPU and 10G of RAM.

I’ve put some load on it (building lang/rust from ports outside poudriere, using make -j2) and the system
started to respond very slowly.

I did break the make process and I was able to look into top where there was:

PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND
0 root -8 - 0B 1808K CPU1 1 35:53 99.79% kernel{arc_prune}
15 root 20 - 0B 16K RUN 0 34:19 99.35% vnlru

The high CPU usage remains even after 30 minutes after the make was stopped.

How can I narrow down the root cause? For the record, the kernel is GENERIC.

Thanks
otis

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Juraj Lutter
XMPP: juraj (at) lutter.sk
GSM: +421907986576



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Juraj Lutter
2024-03-01 19:38:50 UTC
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Post by Juraj Lutter
Hi,
I have a fresh (git b9880e247b26) 13.3-STABLE running in bhyve with 2 vCPU and 10G of RAM.
I’ve put some load on it (building lang/rust from ports outside poudriere, using make -j2) and the system
started to respond very slowly.
PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND
0 root -8 - 0B 1808K CPU1 1 35:53 99.79% kernel{arc_prune}
15 root 20 - 0B 16K RUN 0 34:19 99.35% vnlru
The high CPU usage remains even after 30 minutes after the make was stopped.
How can I narrow down the root cause? For the record, the kernel is GENERIC.
After manually issuing “sync”, the CPU hog stopped and the machine is responding normally now.

It still remains unclear to me why that situation could happen, though.

—
Juraj Lutter
XMPP: juraj (at) lutter.sk
GSM: +421907986576



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Lexi Winter
2024-03-01 19:43:29 UTC
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Post by Juraj Lutter
I have a fresh (git b9880e247b26) 13.3-STABLE running in bhyve with 2 vCPU and 10G of RAM.
I’ve put some load on it (building lang/rust from ports outside poudriere, using make -j2) and the system
started to respond very slowly.
PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND
0 root -8 - 0B 1808K CPU1 1 35:53 99.79% kernel{arc_prune}
15 root 20 - 0B 16K RUN 0 34:19 99.35% vnlru
this could be [0]: "High CPU usage by arc_prune; analysis and fix".

[0] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275594
Juraj Lutter
2024-03-01 19:47:47 UTC
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Post by Lexi Winter
Post by Juraj Lutter
I have a fresh (git b9880e247b26) 13.3-STABLE running in bhyve with 2 vCPU and 10G of RAM.
I’ve put some load on it (building lang/rust from ports outside poudriere, using make -j2) and the system
started to respond very slowly.
PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND
0 root -8 - 0B 1808K CPU1 1 35:53 99.79% kernel{arc_prune}
15 root 20 - 0B 16K RUN 0 34:19 99.35% vnlru
this could be [0]: "High CPU usage by arc_prune; analysis and fix".
[0] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275594
Indeed, the symptoms are very similar. Thanks for the pointer.

—
Juraj Lutter
XMPP: juraj (at) lutter.sk
GSM: +421907986576



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