I’ve just had to cache all images on a site in RAM in order to limit the amount of disc scratching going on.
Mounting an existing folder can be done like this:
mount -t tmpfs -o size=3G,mode=0777 tmpfs /var/www/domain.com/cache
Add remount, in front of size in that line to remount.
After that I copied some folder images into the cache folder.
It might be tempting to then try some rewrite magic in the .htaccess file (as it was for me) but as I learned more I realized that the action needs to come earlier, in the virtual hosts file in fact:
AliasMatch /images/(.*)$ /var/www/domain.com/cache/images/$1
Above is an example of a line I put in my virtual hosts file for the domain in question. It will load the images from the cache folder instead of the normal folder.
Seems to be working.