luokai0 Operating Systems Expert
Before Starting
- Which OS or kernel? (Linux, Windows, embedded RTOS)
- User-space or kernel-space concern?
- Performance, correctness, or security focus?
Core Expertise Areas
Process Management
Process: program in execution — PCB, address space, open files, state. Process states: new, ready, running, waiting, terminated. Context switch: save/restore PCB, TLB flush, cache invalidation — expensive. Threads: lightweight process sharing address space, cheaper context switch. Fork and exec: Unix process creation — copy-on-write optimization.
CPU Scheduling
FCFS: first-come first-served, simple, convoy effect. SJF: shortest job first, optimal average wait, requires future knowledge. Round robin: time quantum, preemptive, fair, context switch overhead. Priority scheduling: starvation risk, aging solution. CFS: Completely Fair Scheduler — Linux default, red-black tree by vruntime.
Memory Management
Paging: fixed-size pages, page table, TLB for fast translation. Segmentation: variable-size segments, segment table, external fragmentation. Virtual memory: demand paging, page faults, swap space. Page replacement: FIFO, LRU, clock algorithm, optimal (Belady). TLB: translation lookaside buffer, O(1) virtual-to-physical translation cache.
Synchronization
Race condition: outcome depends on scheduling order — must be prevented. Mutex: mutual exclusion, binary semaphore, blocks waiting threads. Semaphore: counting semaphore for resource counting, wait and signal. Deadlock: four conditions — mutual exclusion, hold-and-wait, no preemption, circular wait. Deadlock prevention: break one of four conditions. Monitor: high-level synchronization with condition variables.
File Systems
Inode: metadata structure — size, permissions, timestamps, block pointers. Directory: maps names to inodes, hierarchical namespace. Journaling: ext4, NTFS — write-ahead log for crash recovery. Virtual file system: uniform interface across different file system types.
Best Practices
- Always check return values of system calls
- Use RAII for resource management to prevent leaks
- Minimize time holding locks
- Prefer higher-level synchronization over raw mutexes
Common Pitfalls
| Pitfall | Fix |
|---|---|
| Deadlock from lock ordering | Always acquire locks in consistent global order |
| False sharing in cache | Pad data structures to cache line boundaries |
| Zombie processes | Always wait on child processes |
| TLB shootdown overhead | Minimize cross-CPU address space changes |
Related Skills
- linux-expert
- concurrency-expert
- computer-architecture-expert