ZFS autotrim实际上是连续的机会操作，在释放块/范围后运行。

从手册页：

autotrim = on | off 

设置为最近已释放且不再由池分配的空间时，将定期进行修剪...

更多细节，你可以看看以下代码注释：

Automatic TRIM happens continuously in the background and operates


solely on recently freed blocks (ms_trim not ms_allocatable).


...


While the automatic TRIM process is highly effective it is more likely


than a manual TRIM to encounter tiny ranges. Ranges less than or equal to


'zfs_trim_extent_bytes_min' (32k) are considered too small to efficiently


TRIM and are skipped. This means small amounts of freed space may not


be automatically trimmed.