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

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

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");
    }
}

> +	    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)

> +    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.