Creating swapfile on btrfs subvolume: chattr +C fails

[Mic]

@Mic

Somewhere here I read there was a change in the btrfs kernel module resulting that compression and CoW are mutually exclusive (?, not sure, have yet to find the posting).

Found the patch and @dalto 's comment:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0e852ab8974cd2b5946766b2d9baf82c78ace03d

BTRFS swap file with hibernate (update to 2022)

No, it means it automatically disables compression when you disable CoW.

But, in fact, I don’t think that’s relevant to what happened here and I still have no clue!