Hi,
I recently upgraded from v4.0.3 to v5.1 (using Redis).
From past experience I remember that when releasing memory, jemalloc was keeping some 12% (1/8) of the current usage for future use, instead of giving everything back to the OS.
But now, i notice that with v5.1 it doesn't seem to return anything back to the OS.
I assume i'm missing something major, but i can't seem to find it in the release notes, or recent commits / issues.

for example, empty process:

Allocated: 2112024, active: 2469888, metadata: 2909288 (n_thp 0), resident: 5656576, mapped: 11190272, retained: 4014080

Then after doing many allocations (of about 500MB), and then releasing most of them:

Allocated: 1962816, active: 4120576, metadata: 20155656 (n_thp 0), resident: 599027712, mapped: 602001408, retained: 32387072

In v4.0.3 the resident used to shrink back to about 14MB.