[pve-devel] [PATCH installer 1/3] run env: always return proper value for default zfs max arc size

[Christoph Heiss]

In preparation for fixing #6285 [0].

`0` means to just skip writing the module parameter. But (especially)
with the upcoming change in ZFS 2.3 - which makes the size basically
that of the system memory minus 1 GiB - we want to always write some
value.

[0] https://bugzilla.proxmox.com/show_bug.cgi?id=6285

Signed-off-by: Christoph Heiss <c.heiss at proxmox.com>
---
 Proxmox/Install/RunEnv.pm |  9 +++++----
 test/zfs-arc-max.pl       | 42 +++++++++++++++++++++++++--------------
 2 files changed, 32 insertions(+), 19 deletions(-)

diff --git a/Proxmox/Install/RunEnv.pm b/Proxmox/Install/RunEnv.pm
index 407d05c..02c603d 100644
--- a/Proxmox/Install/RunEnv.pm
+++ b/Proxmox/Install/RunEnv.pm
@@ -337,14 +337,15 @@ sub default_zfs_arc_max {
     my $product = Proxmox::Install::ISOEnv::get('product');
     my $total_memory = query_total_memory();
 
-    # By default limit PVE and low-memory systems, for all others let ZFS decide on its own by
-    # returning `0`, which causes the installer to skip writing the `zfs_arc_max` module parameter.
+    # By default limit PVE and low-memory systems, for all just use the 50% of system memory
     if ($product ne 'pve') {
-	return 0 if $total_memory >= 2048 && $product ne 'pmg';
-	return 0 if $total_memory >= 4096; # PMG's base memory requirement is much higer
+	my $zfs_default_mib = int(sprintf('%.0f', $total_memory / 2));
+	return $zfs_default_mib if $total_memory >= 2048 && $product ne 'pmg';
+	return $zfs_default_mib if $total_memory >= 4096; # PMG's base memory requirement is much higher
     }
 
     my $default_mib = $total_memory * $ZFS_ARC_SYSMEM_PERCENTAGE;
+    # int(sprintf()) rounds up instead of truncating
     my $rounded_mib = int(sprintf('%.0f', $default_mib));
 
     if ($rounded_mib > $ZFS_ARC_MAX_SIZE_MIB) {
diff --git a/test/zfs-arc-max.pl b/test/zfs-arc-max.pl
index 8cf093f..a8c0a37 100755
--- a/test/zfs-arc-max.pl
+++ b/test/zfs-arc-max.pl
@@ -21,8 +21,10 @@ sub mock_product {
     );
 }
 
-my %default_tests = (
-    16 => 64, # at least 64 MiB
+use constant ZFS_ARC_MIN_MIB => 64;
+
+my %default_tests_pve = (
+    16 => ZFS_ARC_MIN_MIB, # at least 64 MiB
     1024 => 102,
     4 * 1024 => 410,
     8 * 1024 => 819,
@@ -31,26 +33,36 @@ my %default_tests = (
     1024 * 1024 => 16384, # maximum of 16 GiB
 );
 
-while (my ($total_mem, $expected) = each %default_tests) {
+my %default_tests_others = (
+    16 => ZFS_ARC_MIN_MIB, # at least 64 MiB
+    1024 => 102,
+    4 * 1024 => 2048,
+    8 * 1024 => 4096,
+    150 * 1024 => 76800,
+    160 * 1024 => 81920,
+    1024 * 1024 => 524288,
+);
+
+mock_product('pve');
+while (my ($total_mem, $expected) = each %default_tests_pve) {
     $proxmox_install_runenv->redefine(
 	query_total_memory => sub { return $total_mem; },
     );
 
-    mock_product('pve');
     is(Proxmox::Install::RunEnv::default_zfs_arc_max(), $expected,
-	"$expected MiB should be zfs_arc_max for PVE with $total_mem MiB system memory");
+	"zfs_arc_max should default to $expected for pve with $total_mem MiB system memory");
+}
 
-    mock_product('pbs');
-    is(Proxmox::Install::RunEnv::default_zfs_arc_max(), $total_mem < 2048 ? $expected : 0,
-	"zfs_arc_max should default to `0` for PBS with $total_mem MiB system memory");
+while (my ($total_mem, $expected) = each %default_tests_others) {
+    $proxmox_install_runenv->redefine(
+	query_total_memory => sub { return $total_mem; },
+    );
 
-    mock_product('pmg');
-    is(Proxmox::Install::RunEnv::default_zfs_arc_max(), $total_mem < 4096 ? $expected : 0,
-	"zfs_arc_max should default to `0` for PMG with $total_mem MiB system memory");
-
-    mock_product('pdm');
-    is(Proxmox::Install::RunEnv::default_zfs_arc_max(), $total_mem < 2048 ? $expected : 0,
-	"zfs_arc_max should default to `0` for PDM with $total_mem MiB system memory");
+    foreach my $product ('pbs', 'pmg', 'pdm') {
+	mock_product($product);
+	is(Proxmox::Install::RunEnv::default_zfs_arc_max(), $expected,
+	    "zfs_arc_max should default to $expected for $product with $total_mem MiB system memory");
+    }
 }
 
 my @clamp_tests = (
-- 
2.48.1