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

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

Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
---
 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 1c4811d..d23a04b 100644
--- a/Proxmox/Install.pm
+++ b/Proxmox/Install.pm
@@ -1137,6 +1137,10 @@ _EOD
 
 	    file_write_all("$targetdir/etc/kernel/cmdline", "root=ZFS=$zfs_pool_name/ROOT/$zfs_root_volume_name boot=zfs\n");
 
+	    my $arc_max = Proxmox::Install::RunEnv::clamp_zfs_arc_max(
+		Proxmox::Install::Config::get_zfs_opt('arc_max')) * 1024 * 1024;
+	    file_write_all("$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 9878f55..fded45a 100644
--- a/Proxmox/Install/RunEnv.pm
+++ b/Proxmox/Install/RunEnv.pm
@@ -296,6 +296,44 @@ sub query_installation_environment : prototype() {
     return $output;
 }
 
+our $ZFS_ARC_MIN_SIZE = 64; # 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 $rounded = int(sprintf('%.0f', get('total_memory') / 10));
+    if ($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) = @_;
+
+    return $value if $value == 0;
+
+    my $total_mem = get('total_memory');
+    if ($value > $total_mem) {
+	return $total_mem;
+    } elsif ($value < $ZFS_ARC_MIN_SIZE) {
+	return $ZFS_ARC_MIN_SIZE;
+    }
+
+    return $value;
+}
+
 my $_env = undef;
 sub get {
     my ($k) = @_;
-- 
2.41.0