Function reserve_aligned_lazy 

pub fn reserve_aligned_lazy(
    size: usize,
    align: usize,
    initial_commit: usize,
) -> Option<LazyReservation>

Available on crate feature lazy-commit only.

Reserve size bytes of anonymous virtual memory whose base is aligned to align, committing ONLY the first initial_commit bytes — the rest is reserved but NOT committed (on Windows; on Unix/miri ALL pages are committed, matching the eager path).

See reserve_aligned for the base/align contract. initial_commit must be a non-zero multiple of the runtime page_size() (not the compile-time PAGE) and <= size; size must also be a multiple of page_size(). Violations return None. This stricter contract exists because on Windows, VirtualAlloc(MEM_COMMIT) operates on whole runtime pages and commit_range accepts only offsets that are multiples of page_size(); a size not aligned to page_size() would create an unwritable tail that cannot be committed via the public API.

The returned LazyReservation frees the ENTIRE VA reservation on drop regardless of how much was committed. (Until task #1118 this sentence named Reservation — the wrong type. This function has returned Option<LazyReservation> since task #1051 introduced the watermark-owning wrapper; the reviewer who found it noted that a publication-readiness wave spent three commits resealing exactly this type without reading its own entry point’s rustdoc.) For the failure cause use try_reserve_aligned_lazy.