ZPL can use dmu_tx_assign(TXG_WAIT)
zfs - Zettabyte File System
Originally filed by Matt Ahrens:
The ZPL can use dmu_tx_assign(TXG_WAIT) when it is not holding any locks. This simplifies the code path and reduces the amount of code that needs to be re-run after waiting. This reduces lock contention and CPU time.