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Simple Buddy Allocator

Browser-based buddy memory allocation visualizer, with the original C reference implementation kept in the repository.

Live demo: https://weida.github.io/simplebuddy/

Simple Buddy demo screenshot

Highlights

  • Visualizes allocation, splitting, freeing, and coalescing
  • Shows contiguous memory, split tree, and free_area lists by order
  • Supports step-by-step execution, autoplay, and playback speed control
  • Displays allocated capacity, internal fragmentation, and the buddy formula
  • Pure static HTML, CSS, and JavaScript; no build step required

Project Layout

simplebuddy/
├── README.md
├── .gitignore
├── index.html              # GitHub Pages root entry, redirects to web/
├── assets/
│   └── simplebuddy-demo.png
├── c/                      # C reference implementation
│   ├── buddy.c
│   ├── buddy.h
│   ├── buddytest.c
│   ├── list.h
│   └── Makefile
└── web/                    # Browser visualizer
    ├── index.html
    ├── styles.css
    └── app.js

The c/ and web/ directories are independent.

Algorithm In 60 Seconds

  • Memory is divided into fixed-size pages. This demo uses 16 pages, 64K each
  • Each order has a free list: free_area[order]
  • A block at order i contains 2^i pages
  • Allocation rounds the request up to the smallest power-of-two block
  • If the target order is empty, a larger block is split repeatedly
  • Freeing uses buddy = pfn XOR 2^order to locate the buddy block
  • Coalescing happens only when the buddy is free and has the same order
  • Internal fragmentation = allocated capacity - requested capacity

Run The C Version

cd c
make
./buddytest

Note: the original C code intentionally keeps its older style. Newer GCC versions may fail on implicit function declarations. If compatibility is needed, make that a focused C-only change.

License

MIT License. See LICENSE for details.