With regards to better algorithms than the OS -- jemalloc is not quite there yet. Here is an illuminating discussion between Redis and Jemalloc devs regarding

With regards to better algorithms than the OS -- jemalloc is not quite there yet. Here is an illuminating discussion between Redis and Jemalloc devs regarding this: https://github.com/jemalloc/jemalloc/issues/566 https://github.com/jemalloc/jemalloc/issues/566 Redis will perform its own housekeeping, hence the usage of the term 'active.' AFAIK, rather than metadata being stored for this, there is a periodic active scan and manual measurement. See more here: https://github.com/antirez/redis/pull/3720 https://github.com/antirez/redis/pull/3720