I have set ServerLimit and MaxClients in httpd.conf to be 1024 but apache status always show only 256 requests currently being processed. I found on google that the config should be put pre-virtual global section, but where is that on Virtualmin/Webmin?
To edit Apache config stuff that is outside of virtual servers, you need to go to Webmin’s Apache module:
“Webmin / Servers / Apache Webserver”, then the tab “Global Configuration”, there click “Edit Config Files”. In the file that shows up there you should already find the directives you want to change, in the IfModule mpm_prefork_module block.