The article claims that an allocator that splits memory based on allocation size is called a "buddy allocator". That's misleading: an allocator that allocates an area for each size class is usually called a "slab allocator", while a "buddy allocator" is one that when needed subdivides a memory area with a power of two size into two half-sized areas that are "buddies", does so recursively to satisfy allocations, and coalesces them again when they are free.

E.g. the Linux kernel used (not sure if it's still like this) a buddy allocator to allocate pages and power-of-two blocks of pages and slab allocators to subdivide those pages and allocate data structures.

Another thing that the article doesn't mention that is important is that most production allocators make use of thread-local storage and either have per-thread caches of free blocks or sometimes whole per-thread memory regions. This is to reduce lock contention and provide memory that is more likely to be in the current core's cache.