understand pm.max_children tuning

Question

I have done some investigations and I have found this to calculate and adjust pm.max_children value

https://myshell.co.uk/blog/2012/07/adjusting-child-processes-for-php-fpm-nginx/

but for example :

• I have 8Gb on my server
• I'm hosting 30 websites
• php-fpm average process size around 40mb
• php-fpm max process size around 80mb
• I want to allocate 5Gb max of my memory to php-fpm processes

If I apply this :

pm.max_children = Total RAM dedicated to the web server / Max child process size

So in my case :

pm.max_children = 5120 / 80 = 64

But If I add pm.max_children = 64 on each php-fpm website conf files, this means every website can use 64 children process X size of 1 process (ex 40mb) = 2560Mb

And If we imagine, at the same time, all the 30 website have reach the pm.max_children value, we will have : 2560Mb (max per website) x 30 websites = 76 800 Mb

Am I correct?

Si yes, this means when many websites are hosted on the same server, we have to divide the result of the calcul pm.max_children = 5120 / 80 = 64 by the number of websites hosted (here 30).

So 64 / 30 = 2,1 and pm.max_children = 2 per website

Is it correct or not?

Thanks