[Bug 275594] High CPU usage by arc_prune; analysis and fix

From: <bugzilla-noreply_at_freebsd.org>
Date: Mon, 13 Oct 2025 11:37:27 UTC 
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275594

Nils Beyer <nbe@vkf-renzel.de> changed:

           What    |Removed                     |Added
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                 CC|                            |nbe@vkf-renzel.de

--- Comment #150 from Nils Beyer <nbe@vkf-renzel.de> ---
Hi,

that "arc_prune" misbehaviour still exists on 15.0-BETA1. To reproduce quickly
do the following:

sysctl vfs.zfs.arc.max=536870912
zpool scrub <YOURPOOLNAME>

Here, two threads "arc_prune" with 91% CPU each spawn, and the throughputs of
the SSDs go down to about 5-20MB/s.

To recover:

sysctl vfs.zfs.arc.max=2147483648

(Note: vfs.zfs.arc.max=0 will NOT recover it)


BR,
Nils

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