$ sudo zpool create pp sdb sdc
$ sudo zfs set dedup=on pp
$ sudo chmod ugo+w /pp
$ dd if=/dev/urandom bs=1M count=16 of=/pp/test
$ while :; do zpool sync; done # wait for a few seconds for ddt log to flush
^C
$ sudo zpool ddtprune -p 100 pp

$ rm /pp/test
$ while :; do zpool sync; done # wait for a few seconds for async delete
^C

$ sudo zdb -bcc pp

Traversing all blocks to verify checksums and verify nothing leaked ...

loading concrete vdev 1, metaslab 126 of 127 ...
leaked space: vdev 0, offset 0x40029000, size 8126464
leaked space: vdev 0, offset 0x407ea000, size 262144
leaked space: vdev 1, offset 0x40029000, size 8126464
leaked space: vdev 1, offset 0x407ea000, size 262144
block traversal size 528384 != alloc 17305600 (leaked 16777216)

        bp count:                    77
        ganged count:                 0
        bp logical:             3081216      avg:  40015
        bp physical:             181248      avg:   2353     compression:  17.00
        bp allocated:            528384      avg:   6862     compression:   5.83
        bp deduped:                   0    ref>1:      0   deduplication:   1.00
        bp cloned:                    0    count:      0
        Normal class:          17367040     used:  0.01%
        Embedded log class              0     used:  0.00%

        additional, non-pointer bps of type 0:         31
        Dittoed blocks on same vdev: 34