Custom malloc / free / realloc

High-performance dynamic memory allocator in C. Built for ETH Zürich's systems programming course, CS:APP-style malloc lab. Final submission achieves ~25% less external fragmentation than the reference implementation.

Design

• Segregated free lists — 20 power-of-2 size classes (LIST_LIMT = 20), binned for near-constant-time best-fit.
• Explicit free-list pointers stored inside freed payload (doubly-linked: prev/next).
• Boundary-tag coalescing on every free — adjacent free blocks merge immediately, preventing fragmentation from accumulating.
• Immediate split on allocation when the remainder exceeds MINSIZE = 24B, keeping the free pool usable for small requests.
• Realloc optimization — in-place expansion when the next block is free and large enough, avoiding a copy.
• 8-byte alignment throughout.

Implementation: mm.c (~305 LOC).

Building and testing

make
./mdriver -V -f traces/short1-bal.rep   # tiny sanity trace
./mdriver -V                            # full trace suite

Course: ETH Zürich, Systems Programming and Computer Architecture, 2024.