Tested 16 live. Pool stayed 524288 (no clamp), server held 103.5 GiB and
reported "7.1 GiB left for everything else" at BOTH 15 and 16 — identical
footprint. HALOGEN_HOST_RESERVE_GIB feeds the fit-check budget only; it is not
an allocation, so raising it cannot give RAM back to the co-tenants. Its sole
observable effect above 16 is to take the KV pool away.
16 therefore cost half the fit margin (1.0 vs 2.0 against the engine's 36.5 GiB
requirement) and bought nothing. 15 is strictly better at the same cost.
Recorded the ceiling (16) and the real air levers in the unit comment: pool
262144 frees 7.2 GiB, max_tok 16384 frees 8.4.
Frank
5c4e8a9600