Re: ZFS tunable parameters

[Brad Spencer <brad%anduin.eldar.org@localhost>]

Sotiris Lamprinidis<sotiris%lamprinidis.com@localhost> writes:

> Hi,
>
> I looked into exposing ZFS tunables through sysctl and it seems
> straightforward. Despite being under "dist" I am not sure if this is true 
> upstream, so the patch is directly on arc.c (and I think it'd be tricky to
> implement otherwise).
>
> I tested arc_min and arc_max, and it seems like changes do have an effect
> (e.g. on c, c_max). Additionally tested arc_free_target and it does have
> an effect also.
>
> Here are the new sysctl values on boot on a 8G system:
>
>     vfs.zfs.arc_min = 392903680
>     vfs.zfs.arc_max = 3143229440
>     vfs.zfs.arc_average_blocksize = 8192
>     vfs.zfs.arc_shrink_shift = 7
>     vfs.zfs.compressed_arc_enable = 1
>     vfs.zfs.arc_meta_limit = 785807360
>     vfs.zfs.arc_meta_min = 0
>     vfs.zfs.arc_free_target = 682
>
>
> Cc'ing kre and martin because you worked on the ZFS source last. Hope
> somebody finds this useful and I'd appreciate any feedback!
>
> S.
>
>
> Index: external/cddl/osnet/dist/uts/common/fs/zfs/arc.c
> ===================================================================
> RCS file: /cvsroot/src/external/cddl/osnet/dist/uts/common/fs/zfs/arc.c,v

[snip diff]

Thank you very much for this patch.  I have been struggling with ZFS on
a 8 to 16GB DOMU build system for quite a while and with this patch and
setting the values to what you have listed I was able to perform my
abuse builds without any problems at all.  100% workable with 4 parallel
builds all using the 2 CPUs I give to the DOMU.  Before this I could do
one or two full system builds before I would have to reboot the build
box and I was pretty much unable to do more than 2 parallel builds at a
time without locking the system up.  Clamping the size of the ARC seems
to be the key.  One work around I was trying to use was setting the
maxvnodes to a very low value and that work around could be removed as
well.

I am running this on a -current as of 2026-07-15.  This find is very
much appreciated.  Thanks again.




-- 
Brad Spencer - brad%anduin.eldar.org@localhost