config: avoid sudden downward glitch in max_filter heurisitic

The recent heuristic change, while having good intentions, added a
glitch in the calculation of max_servers to use between the system
memory boundary of 3840 MiB.
For example, if a VM would e.g., have 3.5 GiB memory it would get 26
max_workers, and if a admin then increased this to 4 GiB, it would get
13 max_workers. This also meant that the VM would use less memory with
4 GiB configured, but when one reduces that, the usage would jump up.

Such effects are rather odd, and thus the heuristic was adapted to be
more linear, with basically no decrease of max_servers due to system
memory increasing.

Make the base_usage a 5/8 fraction of the detected total system
memory, fixate the estimation for per-server-memory usage to 150 MiB
and make the warning differ between violating minimum and recommended
total system memory (with some leeway).

A comparission table of system-memory in the first column, previous
max_servers results in the middle (the caller adds +2 to this, which
is done here too) and the result of the updated calculation in right
most column:

GiB     # max old        # max new
0.5       5               5
1.0       9               7
1.5       13              8
2.0       13              10
2.5       17              11
3.0       22              12
3.5       26              13
4.0       13              15
4.5       16              18
5.0       20              22
5.5       23              25
6.0       27              28
6.5       30              32
7.0       34              35
7.5       37              39
8.0       40              40

As flooding tests here could not use much more than 4 to 6 processes,
the slightly lower values on very low-memory systems should not matter
– actually they might improve performance even (less memory
contention and lower OOM-kill possibility).

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

diff --git a/src/PMG/Config.pm b/src/PMG/Config.pm
index e2ab8ed7080f217f85a911ce4e99abb749d7706d..70e182197289364dc5f7659f1ba0687b4e3e1e80 100644 (file)
--- a/src/PMG/Config.pm
+++ b/src/PMG/Config.pm
@@ -457,17 +457,20 @@ sub physical_memory {
 # heuristic for optimal number of smtp-filter servers
 sub get_max_filters {
     my $max_servers = 5;
-    my $per_server_memory_usage = 120;
+    my $per_server_memory_usage = 150;
 
     my $memory = physical_memory();
 
     my $base_memory_usage; # the estimated base load of the system
     if ($memory < 3840) { # 3.75 GiB
-       warn "low amount of system memory installed, recommended is 4+ GB\n";
-       $base_memory_usage = $memory > 1536 ? 1024 : 512;
+       my $memory_gb = sprintf('%.1f', $memory/1024.0);
+       my $warn_str = $memory <= 1900 ? 'minimum 2' : 'recommended 4';
+       warn "system memory size of $memory_gb GiB is below the ${warn_str}+ GiB limit!\n";
+
+       $base_memory_usage = int($memory * 0.625); # for small system assume 5/8 for base system
+       $base_memory_usage = 512 if $base_memory_usage < 512;
     } else {
-       $base_memory_usage = 2816; # 2.75 GiB
-       $per_server_memory_usage = 150;
+       $base_memory_usage = 2560; # 2.5 GiB
     }
     my $add_servers = int(($memory - $base_memory_usage)/$per_server_memory_usage);
     $max_servers += $add_servers if $add_servers > 0;