Recently I was reading the documentation for jemalloc and wondered what actually goes into a custom memory allocator for Rust. To add jemalloc, or any other custom allocator, to a Rust application, one uses the #[global_allocator] macro. Conveniently, the documentation for GlobalAlloc actually has a full example allocator for us to explore. It starts out as follows: const ARENA_SIZE: usize = 128 * 1024; const MAX_SUPPORTED_ALIGN: usize = 4096; #[repr(C, align(4096))] // 4096 == MAX_SUPPORTED_ALI...