127.0.0.1:6379> config set activedefrag yes
(error) ERR Active defragmentation cannot be enabled: it requires a Redis server compiled with a modified Jemalloc like the one shipped by default with the Redis source distribution

So I guess what you are saying is that what I was trying basically isn't possible. I'd need to install Redis completely from source rather than using a yum repo like EPEL or Remi?

I presume the only method that will work is to completely remove Redis and then build all from source? The reason I want to avoid that is because I want to have the active defrag enabled on a production server. If I need to manually upgrade redis each time then I will obviously have more down time and there is a greater possibility for things to go wrong (even if I do test the upgrade via test server) Where as updating via YUM has its clear advantages - assuming you have an up to date repo