> Development of Jemalloc will transition back to the original open source
project: https://github.com/jemalloc/jemalloc. Meta’s fork of the Jemalloc
project will be fully archived as part of the transition. We look forward
to continuing the collaboration with the community to drive jemalloc.
Generally yes, but the wording of "instantly" begs for the following pedantic remark:
This is controlled by jemalloc settings `dirty_decay_ms`, `muzzy_decay_ms`, and their interaction with `background_thread`.
`dirty_decay_ms` currently defaults to 10 seconds, so it's not that instant.
That is important e.g. for single-threaded programs that start other programs, such as my Python example: If it starts a subprocess before the 10 seconds elapse after `free()`, Python (and jemalloc) do not run, and get no chance to return memory to the OS.
In such cases, either enable `background_thread`, or set the `_decay_` values to `0` to ensure immediate return to the OS upon `free()`. (This costs some performance.)
> Development of Jemalloc will transition back to the original open source project: https://github.com/jemalloc/jemalloc. Meta’s fork of the Jemalloc project will be fully archived as part of the transition. We look forward to continuing the collaboration with the community to drive jemalloc.
> See blog post for details: https://engineering.fb.com/2026/03/02/data-infrastructure/in...