Comment by Svetlitski

As of when I left Meta nearly two years ago (although I would be absolutely shocked if this isn’t still the case) Jemalloc is the allocator, and is statically linked into every single binary running at the company.

> Or I wonder if they could simply use tcmalloc or another allocator these days?

Jemalloc is very deeply integrated there, so this is a lot harder than it sounds. From the telemetry being plumbed through in Strobelight, to applications using every highly Jemalloc-specific extension under the sun (e.g. manually created arenas with custom extent hooks), to the convergent evolution of applications being written in ways such that they perform optimally with respect to Jemalloc’s exact behavior.