Re: [pve-devel] [PATCH installer v2 1/6] fix #4829: install: add new ZFS `arc_max` setup option

[Christoph Heiss <c.heiss@proxmox.com>]

Thanks for the review!

I will refactor all the points mentioned and send a v2 soon.

On Tue, Oct 24, 2023 at 05:05:15PM +0200, Thomas Lamprecht wrote:
>
> Am 24/10/2023 um 13:55 schrieb Christoph Heiss:
> > Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
> > ---
> > Changes v1 -> v2:
> >   * No changes
> >
> >  Proxmox/Install.pm        |  4 ++++
> >  Proxmox/Install/Config.pm |  1 +
> >  Proxmox/Install/RunEnv.pm | 38 ++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 43 insertions(+)
> >
> > diff --git a/Proxmox/Install.pm b/Proxmox/Install.pm
> > index 1117fc4..0c3541f 100644
> > --- a/Proxmox/Install.pm
> > +++ b/Proxmox/Install.pm
> > @@ -1141,6 +1141,10 @@ _EOD
> >
> >  	    file_write_all("$targetdir/etc/kernel/cmdline", "root=ZFS=$zfs_pool_name/ROOT/$zfs_root_volume_name boot=zfs\n");
> >
> > +	    my $arc_max = Proxmox::Install::RunEnv::clamp_zfs_arc_max(
> > +		Proxmox::Install::Config::get_zfs_opt('arc_max')) * 1024 * 1024;
>
> Mixing multiplication and method call this way is a bit hard to read.
>
> Maybe move the clamping into  out to its own local method, something like:
>
> my sub setup_zfs_conf {
>     my ($target_dir) = @_;
>
>     my $arc_max_mb = Proxmox::Install::Config::get_zfs_opt('arc_max');
>     my $arc_max = Proxmox::Install::RunEnv::clamp_zfs_arc_max($arc_max_mb) * 1024 * 1024;
>
>     if ($arc_max > 0) {
>         file_write_all("${target_dir}/etc/modprobe.d/zfs.conf", "options zfs zfs_arc_max=$arc_max\n");
>     }
> }

Seems like a good idea, the extract_data() sub is _way_ to overloaded
already anyway.

>
> > +	    file_write_all("$targetdir/etc/modprobe.d/zfs.conf", "options zfs zfs_arc_max=$arc_max\n")
> > +		if $arc_max > 0;
>
>
> >  	}
> >
> >  	diversion_remove($targetdir, "/usr/sbin/update-grub");
> > diff --git a/Proxmox/Install/Config.pm b/Proxmox/Install/Config.pm
> > index 024f62a..f12ae67 100644
> > --- a/Proxmox/Install/Config.pm
> > +++ b/Proxmox/Install/Config.pm
> > @@ -72,6 +72,7 @@ my sub init_cfg {
> >  	    compress => 'on',
> >  	    checksum => 'on',
> >  	    copies => 1,
> > +	    arc_max => Proxmox::Install::RunEnv::default_zfs_arc_max(),
> >  	},
> >  	# TODO: single disk selection config
> >  	target_hd => undef,
> > diff --git a/Proxmox/Install/RunEnv.pm b/Proxmox/Install/RunEnv.pm
> > index c9d788b..9236030 100644
> > --- a/Proxmox/Install/RunEnv.pm
> > +++ b/Proxmox/Install/RunEnv.pm
> > @@ -301,6 +301,44 @@ sub query_installation_environment : prototype() {
> >      return $output;
> >  }
> >
> > +our $ZFS_ARC_MIN_SIZE = 64; # MiB
> > +
> > +# Calculates the default upper limit for the ZFS ARC size.
> > +# See also https://bugzilla.proxmox.com/show_bug.cgi?id=4829 and
> > +# https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%20Parameters.html#zfs-arc-max
> > +sub default_zfs_arc_max {
> > +    # Use ZFS default on non-PVE
> > +    return 0 if Proxmox::Install::ISOEnv::get('product') ne 'pve';
> > +
> > +    my $max = 16 * 1024; # 16 GiB
> > +
> > +    my $rounded = int(sprintf('%.0f', get('total_memory') / 10));
>
> knowing in what units this is calculating/returning would be great here
> (via comment and/or variable name)
Definitely sensible, I will rename + expand the comments a bit more.

>
> > +    if ($rounded > $max) {
> > +	return $max;
> > +    } elsif ($rounded < $ZFS_ARC_MIN_SIZE) {
> > +	return $ZFS_ARC_MIN_SIZE;
> > +    }
> > +
> > +    return $rounded;
> > +}
> > +
> > +# Clamps the provided ZFS arc_max value to the accepted bounds. See also
> > +# https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%20Parameters.html#zfs-arc-max
> > +sub clamp_zfs_arc_max {
> > +    my ($value) = @_;
>
> please at least comment, or better, name variables accordingly, in what
> units your dealing here, I think MB?
>
> When I worked on the partition sizing code it was a PITA to trace what
> unit was used when.