This is a problem that affects many Moodle sites, but now has a surprisingly simple solution.
So you have Manual Enrolment enabled in a Moodle course.
You have say 2,000 users on the system.
When you try and Enrol users, you get a message in the selection area that says “Too many users”.
How on earth are you going to select the couple of hundred users you need easily?
The fact is that Moodle is setup by default to display a maximum of 100 users in operations like this – for performance reasons. Imagine if you had 50,000 users … how long the list would be, and the strain it would put on the server doing listing these.
Initially you couldn’t change this without changing Moodle core code – the limit of 100 users displayed was hard coded (in multiple locations).
But now an administrator can go to:
Site Administration > Users > Permissions > User Policies
On this page you can set a new value for “Maximum users per page.”
I’ve increased this to 1,000 and even 5,000 on a few client sites, and it seems to work well (but if your server is struggling and you have huge numbers it may cause a slowdown if you are listing many users like this multiple times).
Anyway – like I said – simple answer and a real time saver.