Nginx/PHP memory settings configuration for file uploads

Hello,

My situation is the following: I have a web application in which users can upload pictures, which are handled by a PHP script using the GD library to make some transformations on the size and quality.

Because it took such a long time to process the files I decided to upgrade the VPS from the 512MB/1 core to 2GB/2 cores, and set the php memory_limit to 900MB (it is correctly set, I can see it with phpinfo()), but this hardly improved anything.

This made me think that there is probably something I should change concerning Nginx, but I cannot seem to figure out what it is (I have unsuccessfully researched a while already). The configuration I have on nginx is pretty much the default one, I barely changed anything since the installation.

Hopefully someone knows the solution or can point me to where to find it.

Thanks a lot in advance!