Our vhosts are filling the memory on the server with old php-fpm processes, we believe this is due to the dynamic max_spare_servers setting.
With this set to 8 (as it seems to be dynamically), we are seeing very large consistent memory usage (~50GB) across as relatively small set of vhosts (~60).
Example pool file:
[164448877221794]
user = test
group = test
listen.owner = test
listen.group = test
listen.mode = 0660
listen = 127.0.0.1:8064
pm = dynamic
pm.max_children = 16
pm.start_servers = 2
pm.min_spare_servers = 1
pm.max_spare_servers = 8 ; <- Far too high
php_value[upload_tmp_dir] = /home/test/tmp
php_value[session.save_path] = /home/test/tmp
php_value[log_errors] = On
php_admin_value[upload_max_filesize] = 40M
php_admin_value[post_max_size] = 40M
These 8x child processes per vhost really add up and in most situations do not need to be there. Unless you are expecting very high levels of traffic you never really need 8x processes on standby, 1 or 2 is nearly always sufficient and more will be spun up as needed.
From the PHP-FPM doc comments:
; pm.max_spare_servers - the maximum number of children in 'idle'
; state (waiting to process). If the number
; of 'idle' processes is greater than this
; number then some children will be killed
If the default settings donât fit
your needs edit them in either the php settings per domain or in the template for newly created domains. These settings are variable on use, for example I use what virtualmin sets however I donât use any form of popular software which may or may not push fpm to itâs limits. I may not explained this well but there are always translation problems, forgive me if this is incorrect
Unfortunately I donât believe this max_spare_servers value can be edited or customised because itâs dynamically generated based on the value of the max servers.
I think the advice in your screenshot is valid assuming you are running a single pool on the server, where you want to maximise throughput on a single site, I would say this is not typical for your average Virtualmin server.
You can update the âServer Templateâ if youâd like to have each Virtual Server adjusted to your preferred setting.
*** These changes will apply to NEW Virtual Servers going forward ***
However, in order to affect this change on existing Virtual Servers, youâll need to âdisableâ Apache and Apache SSL (or Nginx equiv) then re-enable it. When disabling, it simply deletes the server CONFIG not the files in your âpublic_htmlâ folder.
The page to edit for PHP defaults would be:
System Settings > Server Templates > Default Settings > PHP Options
You should be aware that memory use for processes like PHP-FPM is not a simple additive equation. Most of that will be shared across processes, as it is all identical pages of shared libraries and such.
Thatâs not to say that may not be an unnecessary amount of processes if this is a lightly loaded site, but also itâs useful to understand whatâs actual unique usage and whatâs shared.
