Ubuntu Swapper：如何优化交换使用

Optimizing Swap Usage in Ubuntu: A Step-by-Step Guide

Swap space is critical for managing virtual memory in Ubuntu, ensuring system stability when physical RAM is exhausted. However, improper swap configuration can lead to performance degradation (e.g., excessive disk I/O) or wasted storage. Below are actionable steps to optimize swap usage, tailored to modern Ubuntu versions (16.04 and later).

1. Adjust Swap File Size Based on System Needs

The swap file size should align with your system’s memory capacity and usage patterns. Follow these guidelines:

• Check current swap status: Run sudo swapon --show to view enabled swap files/partitions and free -h to see total swap space.
• Create/resize a swap file (recommended over partitions for flexibility):
  • Disable existing swap (if any): sudo swapoff /swapfile.
  • Create a new swap file (e.g., 4GB): sudo fallocate -l 4G /swapfile.
  • Set secure permissions: sudo chmod 600 /swapfile (prevents unauthorized access).
  • Format the file as swap: sudo mkswap /swapfile.
  • Enable the swap file: sudo swapon /swapfile.
• Make it permanent: Add /swapfile none swap sw 0 0 to /etc/fstab (backup the file first).
• Recommended sizes:
  • Physical RAM ≤ 2GB: Swap = 2× RAM (e.g., 2GB RAM → 4GB swap).
  • 2GB < RAM ≤ 8GB: Swap = RAM size (e.g., 4GB RAM → 4GB swap).
  • RAM > 8GB: Swap = 4–8GB (sufficient for most desktop users; servers may need less).
  • Hibernate support: If using hibernation, swap must be at least RAM + 2GB (e.g., 8GB RAM → 10GB swap).

2. Tune the swappiness Kernel Parameter

swappiness controls how aggressively the kernel moves data from RAM to swap (range: 0–100). A lower value reduces swap usage, improving performance for systems with ample RAM.

• Check current value: cat /proc/sys/vm/swappiness (default: 60).
• Temporarily adjust: sudo sysctl vm.swappiness=10 (reduces swap activity; ideal for desktops).
• Permanently set: Add vm.swappiness=10 to /etc/sysctl.conf, then run sudo sysctl -p to apply changes.

3. Use Faster Storage for Swap

Swap performance heavily depends on storage speed. Prioritize:

• SSD/NVMe: Place the swap file on an SSD (or NVMe drive) to minimize latency. Avoid mechanical hard drives (HDDs) if possible, as they significantly slow down swap operations.
• Separate partitions: For dedicated swap partitions, ensure they are on a fast storage device (e.g., /dev/sda1 instead of /dev/sdb1).

4. Enable Zswap for Memory Compression

Zswap compresses swap data in RAM before writing it to disk, reducing disk I/O and improving performance. It’s ideal for systems with limited RAM.

• Enable Zswap: Edit /etc/default/grub and add these parameters to the GRUB_CMDLINE_LINUX_DEFAULT line:
  zswap.enabled=1 zswap.compressor=lz4 zswap.max_pool_percent=20 (adjust max_pool_percent based on your RAM size; 20% is a good starting point).
• Update GRUB and reboot: Run sudo update-grub followed by sudo reboot to apply changes.

5. Monitor Swap Usage Regularly

Regular monitoring helps identify excessive swap usage (indicating a need for more RAM or tuning). Use these commands:

• View swap/ram usage: free -h (shows total, used, and free swap/ram in a human-readable format).
• Monitor real-time swap activity: vmstat 1 (check si [swap in] and so [swap out] columns; high values indicate frequent swap usage).
• Long-term analysis: Use tools like gnome-system-monitor (GUI) or sar (CLI) to track swap trends over time.

6. Remove Unnecessary Swap Files/Partitions

Multiple swap files/partitions can waste resources and degrade performance.

• Disable unused swap: Run sudo swapoff /swapfile (replace with your swap file path).
• Delete the swap file: sudo rm /swapfile.
• Update /etc/fstab: Remove the corresponding line (e.g., /swapfile none swap sw 0 0) to prevent automatic mounting on boot.

7. Consider zRAM for Compressed RAM Swap

zRAM creates a compressed block device in RAM, acting as swap space. It’s faster than disk-based swap (since it avoids disk I/O) and ideal for systems with limited RAM.

• Install zRAM tools: sudo apt install zram-config (available in Ubuntu repositories).
• Configure zRAM: The tool automatically creates a compressed swap device (typically 50% of RAM). Adjust settings in /etc/default/zramswap if needed (e.g., ALGO=lz4 for better compression).

8. Increase Physical RAM (Best Long-Term Solution)

Swap is a temporary fix for insufficient RAM. If your system frequently uses swap (evident from free -h or vmstat), consider upgrading your RAM. This eliminates reliance on slow disk-based swap and improves overall performance.

By following these steps, you can optimize Ubuntu’s swap usage to balance performance and stability. Remember: the best approach depends on your system’s hardware (RAM, storage type) and usage patterns (desktop vs. server). Always back up critical data before making system changes.