Slow I/O from time to time.

[clouds56]

I'm running fedora (rawhide) in guest, with btrfs. And found that sometimes it takes long for I/O to respond.
Even ls takes several seconds to respond, and I found that in "System Monitor",

• ls command started at around "30secs"
• The ls finished just before the orange peak between "20secs" and "10secs"
• It's about 1.5MB disk writing (not reading)
• After ls finished, I run another ls and it completes immediately.
• But if I run ls after some time (minutes), it hangs for another several seconds.
• During this "hang", GUI of guest works perfectly, and the CPU usage is low.

Any Idea what happens? Why ls need to write disk?
It's my first time to use btrfs so I'm not sure if it has something to do with the format.

MacBook Pro, M2, macOS 15.1.1
UTM Version 4.6.2 (100)
Linux fedora 6.13.0-0.rc0.20241126git7eef7e306d3c.10.fc42.aarch64 #1 SMP PREEMPT_DYNAMIC Tue Nov 26 15:37:41 UTC 2024 aarch64 GNU/Linux
Use Apple Virtualization with Rosetta enabled.