LC

Implement Copy-on-Write (COW) for fork() Efficiency

hard6/10

Implement Demand Paging: Allocate on First Access Explore Huge Pages: Benchmark 4KB vs 2MB Pages

Language

Compiler

2.0s Limit 256MB

Implementation

Implement copy-on-write fork().

Requirements:

Track pages with ref_count (how many processes share)
fork() marks pages read-only, increments ref_count
Write triggers COW page fault
COW handler: copy page if ref_count > 1, make writable
Track pages copied due to COW
Print COW statistics
Show memory savings

Test:

fork() copies page tables (fast)
Write triggers COW fault
Only written pages copied

Why This Matters

Every fork() on Linux relies on copy-on-write to make process creation cheap, and Redis's BGSAVE forks its entire dataset to get a consistent snapshot using this exact mechanism. The 2016 Dirty COW vulnerability (CVE-2016-5195) exploited a race in this very write-fault path to let unprivileged users gain root, showing COW correctness is a security property, not just a performance one.

Hints

0 / 3 revealed

Validation Suite

main.c

Workspace 1.0