LFCS Operation of Running Systems Practice Question
A systems administrator is troubleshooting a server that runs a database application. The server has 64 GB of RAM and 16 CPU cores. The administrator notices that the system is using a significant amount of swap space even though there is plenty of free memory. The 'free -m' command shows: total memory = 65536, used = 50000, free = 15536, buffers/cache = 10000, swap total = 8192, swap used = 6000. Which of the following is the most likely cause?
⚠ Common exam trap
Linux Foundation often tests the misconception that swap usage only occurs when memory is full, but the trap here is that vm.swappiness can cause swapping even with abundant free memory, leading candidates to overlook the kernel's proactive swapping behavior.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The vm.swappiness value is set too high.
A high vm.swappiness value (default 60) causes the kernel to aggressively swap out anonymous pages even when ample free memory exists. With 15 GB free and 10 GB in buffers/cache, the system should not be using 6 GB of swap unless swappiness is set too high, forcing premature swapping.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The vm.dirty_ratio and vm.dirty_background_ratio are set too high.
Why it's wrong here
These parameters control how much dirty page cache can accumulate. High values could cause more I/O, but not necessarily swap usage.
- ✓
The vm.swappiness value is set too high.
Why this is correct
A high swappiness value (e.g., 100) makes the kernel more likely to swap pages out to disk even when there is free memory available.
- ✗
The database is configured to use huge pages, which are not swappable.
Why it's wrong here
Huge pages are not swappable, so they would reduce swap usage, not increase it.
- ✗
The vm.vfs_cache_pressure is set too low.
Why it's wrong here
A low vfs_cache_pressure causes the kernel to retain filesystem cache, which would use memory, not swap. This would decrease swap usage.
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Written by Johnson Ajibi, MSc IT Security
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