pub const CLUSTER_SHIFT: u32 = 21;Expand description
log2 of the read-only materialization cluster size. 21 → 2 MiB, the
common large-page size on x86 (PDE), AArch64 (L2 block), and RISC-V
(megapage), so the clustered charge model is arch-portable.
TODO(gas-calibration): cluster size is subject to change.