I have a very high I/O load on the server which causes 500 error many times per day while the CPU/RAM usage is basically non exsitent:

the main work of the server is serving images and videos. I'll focus the question on images and leave videos for another question.

This is the code for serving images:

$file = $_GET['n'];
$path = $root . '/memes/' . getDir($file) . '/' . $file;

header('Content-Type: image/jpeg');
header('Content-Disposition: inline; filename="' . $file . '"');
header('Content-Length: ' . filesize($path));
header('Cache-control: max-age='.(60*60*24*365));
readfile($path);

I guess header('Cache-control: max-age='.(60*60*24*365)); is for browser..

How can I cache the image into RAM and then serve it from there instead of putting the load on the SSD hunderts of times for the same image with PHP? I also need to set expire time, so if a specific image doesn't get requested for like 5 minutes it should be removed from the RAM / cache.

I want to make use of the CPU and RAM instead of letting them being almost useless :D