Can I ask you a dumb question: I think I just turned it on properly but I have no idea how to proactively confirm that mysql is actually using jemalloc, rather than just wait for better performance numbers?

Because it's an external environment variable, it doesn't actually show inside any of mysql's settings. No startup errors or runtime problems is always nice but I really am curious to know for a fact it worked.

Will probably have to ask this on stackexchange if you don't know.

With tcmalloc I get a few messages in the log about a large allocation on startup, but you can probably find it with this.

    # as root or sudo
    pmap -x $(pidof mysqld)|grep malloc