> The second is an implementation detail of the linux swap file code.  It
quoted text
> expects filesystems don't move blocks around, and takes a mapping of the
> blocks in the FS once.
> 
> This doesn't work with btrfs because we do move blocks around all the
> time.

That's interesting. I have a few questions:

-Is creating a loopback device from the file any different, or does that
lead to the same problems?

-Would mounting a filesystem image via loopback device cause similar
problems?

-Would this be viable if using a dedicated nodatacow subvolume, or is that
still too risky because of the odd case where you do cow?

-Does online defragmentation hurt this as well?

Cheers,

-Anthony

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