- Always try to write one whole page at a time.

- Always try to write one whole page at a time.
- vm_page_undirty() is enough (instead of vm_page_set_validclean()), but it has
  to be called before we write the data in case someone makes page dirty after
  our write, but before our vm_page_undirty() call.
- Always dmu_write, not matter if uiomove() succeeded, because it could
  partially be ok and we would lose some changes.

All good ideas from:	ups