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

From: <bugzilla-noreply_at_freebsd.org>
Date: Fri, 15 Mar 2024 07:59:06 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275594

--- Comment #89 from Felix Palmen <zirias@freebsd.org> ---
(In reply to Seigo Tanimura from comment #87)

On my home server (amd64, 4x 4TB spinning HDDs with GELI partitions and a
raid-z1 pool on top, arc_max 32GiB, neither l2arc nor zil), I had issues with
stalls (1 to several seconds) under heavy I/O load (with poudriere and nullfs
involved) ever since upgrading to FreeBSD 13.x.

With the 13.3 kernel, the issue escalated from "pretty annoying" to "completely
unusable".

Now after applying all your patches, it is a *lot* better. I could still
provoke stalls having a large poudriere build with heavy ccache usage and at
the same time using a Windows Server VM with zvol storage backend on the same
pool ... but I guess there are limits somewhere ;) will continue to observe the
overall behavior.

so:
1. Thanks a lot for this awesome work!
2. Please get it merged to all affected branches :)

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