What is malloc doing, anyway?

	What is malloc doing, anyway?(benmandrew.com)
	255 points by benmandrew 2 days ago \| 64 comments
	tl;dr: The article walks through building a toy malloc from scratch using sbrk and mmap, explaining chunk headers, free lists, splitting/coalescing, demand paging, and trimming the heap back to the kernel. Benchmarks show the toy allocators run 65-150x slower than glibc, which stays fast by using size-segregated bins, a thread-local cache (tcache) of recently freed chunks, and an adaptive mmap threshold—trading memory overhead to avoid syscalls on the hot path.
	HN Discussion: ↓The article describes an obsolete brk-based allocator; modern allocators like jemalloc/mimalloc work differently ~Recommends alternative learning resources for understanding modern allocators and memory management ↑Shares personal experience building custom malloc implementations as valuable learning exercises •The malloc interface itself is poorly designed (no alignment control, no allocation size reporting) •Interest in alternatives that avoid malloc complexity entirely, like stack-only languages