feat(fork): Copy-on-Write page sharing with comprehensive test suite #79
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Replace full page copying with CoW semantics for efficient fork(): - Add frame_metadata.rs: reference counting for shared physical frames - Add COW_FLAG (BIT_9) in process_memory.rs for marking CoW pages - Modify setup_cow_pages() to share frames instead of copying - Add handle_cow_fault() in interrupts.rs for lazy page copying - Add frame deallocation support in frame_allocator.rs - Add cleanup_cow_frames() in process.rs for exit cleanup When fork() is called: 1. Parent pages are marked read-only with COW_FLAG 2. Same physical frames are mapped in child with COW flags 3. Reference counts are incremented for shared frames 4. On write fault: allocate new frame, copy data, update mapping This significantly reduces fork() memory usage and latency for processes with large address spaces. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add rigorous test coverage for Copy-on-Write fork implementation: Tests added: - cow_signal_test: Signal + CoW interaction, deadlock prevention - cow_cleanup_test: Frame refcount cleanup on child exit - cow_sole_owner_test: Verifies SOLE_OWNER_OPT counter increments - cow_stress_test: 128 pages (512KB) scale testing - cow_readonly_test: Read-only code section sharing - cow_oom_test: Graceful OOM handling during CoW faults Infrastructure: - sys_cow_stats syscall (500): Exposes kernel CoW counters - sys_simulate_oom syscall (501): Test-only OOM simulation - cow_stats module in interrupts.rs for tracking fault paths The cow_sole_owner_test uses kernel counter verification to prove the optimization path was actually taken, not just that writes succeeded - addressing test integrity concerns. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
This was referenced Jan 10, 2026
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Summary
Features
CoW Fork Implementation
Test Suite (6 new tests)
New Syscalls (test infrastructure)
sys_cow_stats(500): Exposes kernel CoW counters to userspacesys_simulate_oom(501): Test-only OOM simulation mechanismTest plan
🤖 Generated with Claude Code