Comment # 1 on bug 1127701 from Stanislav Brabec

It requires another way to de-duplicate.

fstrim -A works perfectly as long as fstab contains device names. If the source
is specified by UUID=, then it fails to de-duplicate.

Tested on this setup:

Works:
/dev/loop0 /mnt/1 btrfs defaults 0 0
/dev/loop0 /mnt/2 btrfs subvol=/subvol 0 0
/dev/loop0 /mnt/3 btrfs subvol=/subvol2 0 0

Broken:
UUID=cb4cf1ab-b586-4980-bd7f-92422bc8f082 /mnt/1 btrfs defaults 0 0
UUID=cb4cf1ab-b586-4980-bd7f-92422bc8f082 /mnt/2 btrfs subvol=/subvol 0 0
UUID=cb4cf1ab-b586-4980-bd7f-92422bc8f082 /mnt/3 btrfs subvol=/subvol2 0 0

Additionally, /dev/root also needs testing (in case, when subvolumes use real
device name).