It could depend on your distro, official packaging (docker,Debian,Fedora) have MALLOC_TRIM_THRESHOLD_=131072 , but different distros could have (or not) ship with different settings.

Official settings for systemd https://github.com/jellyfin/jellyfin-packaging/blob/master/debian/conf/jellyfin

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The value of this tunable is the minimum size (in bytes) of the top-most, releasable chunk in an arena that will trigger a system call in order to return memory to the system from that arena.

https://www.gnu.org/software/libc/manual/html_node/Memory-Allocation-Tunables.html

MALLOC_MMAP_THRESHOLD_ is an environment variable that sets the size threshold for using the mmap system call to allocate memory instead of using the heap.

• Default: 128 KiB
• Behavior:
  • If a memory request is ≥ 128 KiB, mmap is used.
  • If < 128 KiB, the heap is used.
• Purpose:
  • Helps manage large memory allocations more efficiently.
  • Can be adjusted to optimize performance for specific applications.