PHP-FPM

PHP-FPM is a gateway that allows running php processes in parallel and processing multiple requests through them. A server (like Caddy and Nginx) typically communicates with the php-fpm socket (or port) to render dynamic pages in PHP software (like MediaWiki).

Configuration

Configuration folder of php (for version 8.4) is /etc/php/8.4/ (notice the last subfolder changes according to version). Within that folder there are different configurations for different ways php is invoked (apache, cli, fpm). When using PHP-FPM, the configuration in the fpm folder is what matters.

Within fpm/pool.d you find the configurations for different process pools. By default only www.conf might be present. Within that you can find the path to unix socket (listen), configure number of child processes, etc.

Increasing max upload

In /etc/php/8.4/fpm/php.ini set post_max_size and upload_max_filesize variables.

Increasing workers for www pool

In /etc/php/8.4/fpm/pool.d/www.conf set pm = dynamic and pm.max_children, pm.start_servers, pm.min_spare_servers, pm.max_spare_servers as appropriate.