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

From: <bugzilla-noreply_at_freebsd.org>
Date: Fri, 08 Dec 2023 17:47:28 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275594

--- Comment #8 from Seigo Tanimura <seigo.tanimura@gmail.com> ---
(In reply to Seigo Tanimura from comment #7)

Done.

Build time: 07:14:10 (295 pkgs / hr)
ARC memory size: ~5.8GB just when the final build finished, ~4.0 GB after
cleaning up all of the poudriere builders.

The final performance was rather like the case of
vfs.vnode.vnlru.max_free_per_call=10000.  arc_prune kept the CPU usage of 20 -
40% after the build of lang/gcc12 until the end.

Inside the ARC memory, "Other" of top(1) recorded ~2.0GB just when the final
build finished.  This value is the sum of:

- kstat.zfs.misc.arcstats.bonus_size
- kstat.zfs.misc.arcstats.dnode_size
- kstat.zfs.misc.arcstats.dbuf_size

Maybe I have work out the way to track them...

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