Implement Buddy Allocator for Physical Memory Management

Power-of-Two Physical Pages

The buddy allocator splits and merges power-of-two blocks of physical memory. Linux's page_alloc.c uses it for page-sized (and larger) allocations because coalescing is O(log n) with simple bitwise buddy math.

Split and Coalesce

Allocation of 200 KB from a 1024 KB arena:

Round up to 256 KB (next power of two)
Split 1024 into two 512 blocks, then split one 512 into two 256
On free, merge buddies if both are free: buddy = addr XOR size

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Why This Matters in Production

Linux's physical page allocator in mm/page_alloc.c is a buddy system just like this one, tracking per-order free lists and coalescing blocks via the same base-address XOR trick to fight external fragmentation. Get the splitting or coalescing logic wrong and you reproduce the exact class of bug kernel developers chase when large contiguous allocations mysteriously fail under memory pressure.

Debugging Checklist

Before you call the implementation done, walk failure modes on purpose. Test empty structures, single-element edge cases, maximum concurrency, and errno paths that must not crash the program. OS code usually fails in production when happy-path tests pass but invariants break under contention or memory pressure.

Implementation Notes

Keep structures small and name fields after kernel counterparts when possible. That lets you read man pages and kernel source side by side while you work. Print observable events during development; remove noisy logs once tests pass reliably.

For This Exercise

You will implement free lists per order, split on alloc, and merge on free. This exercise asks you to print the tree after each operation so fragmentation behavior is visible.

Implement buddy system allocator for physical memory.

Requirements:

Define Block structure with size, status, next pointer
Maintain array of free lists (one per power-of-2 size)
Implement buddy_alloc(size) to allocate memory
Implement buddy_free(ptr) to free memory
Implement buddy_find_buddy(ptr) to find buddy block
Implement buddy_coalesce(ptr) to merge with buddy if free
Support memory sizes from 1 KB to 1024 KB (powers of 2)
Print allocation, splitting, and coalescing events
Handle out-of-memory conditions
Track allocated blocks and free blocks
Demonstrate with example allocation pattern

Power-of-Two Physical Pages

Split and Coalesce

Allocation of 200 KB from a 1024 KB arena:

Round up to 256 KB (next power of two)
Split 1024 into two 512 blocks, then split one 512 into two 256
On free, merge buddies if both are free: buddy = addr XOR size

c
Loading…

Why This Matters in Production

Debugging Checklist

Implementation Notes

For This Exercise

You will implement free lists per order, split on alloc, and merge on free. This exercise asks you to print the tree after each operation so fragmentation behavior is visible.

Implement buddy system allocator for physical memory.

Requirements:

Define Block structure with size, status, next pointer
Maintain array of free lists (one per power-of-2 size)
Implement buddy_alloc(size) to allocate memory
Implement buddy_free(ptr) to free memory
Implement buddy_find_buddy(ptr) to find buddy block
Implement buddy_coalesce(ptr) to merge with buddy if free
Support memory sizes from 1 KB to 1024 KB (powers of 2)
Print allocation, splitting, and coalescing events
Handle out-of-memory conditions
Track allocated blocks and free blocks
Demonstrate with example allocation pattern

Topic Overview

Power-of-Two Physical Pages

Split and Coalesce

Why This Matters in Production

Debugging Checklist

Implementation Notes

For This Exercise

Implementation Task

Progressive Hints

Resources

Open Source

Implement Buddy Allocator for Physical Memory Management

Topic Overview

Power-of-Two Physical Pages

Split and Coalesce

Why This Matters in Production

Debugging Checklist

Implementation Notes

For This Exercise

Implementation Task

Progressive Hints

Resources

Open Source