musl/src/malloc/DESIGN

In principle, this memory allocator is roughly equivalent to Doug
Lea's dlmalloc with fine-grained locking.



malloc:

Uses a freelist binned by chunk size, with a bitmap to optimize
searching for the smallest non-empty bin which can satisfy an
allocation. If no free chunks are available, it creates a new chunk of
the requested size and attempts to merge it with any existing free
chunk immediately below the newly created chunk.

Whether the chunk was obtained from a bin or newly created, it's
likely to be larger than the requested allocation. malloc always
finishes its work by passing the new chunk to realloc, which will
split it into two chunks and free the tail portion.