[Request]: Storage - Automatically reclaim unused disk space from containers with minimal user interaction

[realrajaryan]

Feature or enhancement request details

Container disk images currently grow over time but never shrink. As containers create and delete data, freed blocks inside their filesystems are not automatically released to the host, leading to permanently increasing disk utilization. This results in wasted space for long-lived containers and unnecessary manual intervention to recover capacity.

To address this, we should automatically reclaim freed blocks from container filesystems using fstrim with minimal user interaction, this way users do not need to manually intervene or recreate containers to reclaim disk space.

Some implementation options:

• Online fstrim: Run fstrim while the container is active to release deallocated blocks to the host.
• Periodic cleanup: Execute fstrim periodically within vminitd for automated cleanup.
• Continuous discard: Mount filesystems with the discard option for continuous trimming.
• Manual offline shrink: Allow users to run container shrink <id> to launch a temporary VM, mount the image, run fstrim and shut down.

Code of Conduct

• I agree to follow this project's Code of Conduct

[RahulThennarasu]

I'd like to try and work on this and have some questions. Which approach would you prefer? Periodic cleanup in vminitd seems reasonable but not sure how often to run it. For online fstrim, would this be automatic at intervals or triggered by some threshold? Are there any concerns about running fstrim on active filesystems in terms of performance impact?

Seems interesting to do research on!