More on this subject: - MEMORY_OBJECT_COPY_DELAY is actually needed to be able to provide private mmaps without copying the entire object at once. - This attribute only changes the behavior of vm_object_copy_strategically, between doing a delayed copy (COPY_DELAY) or copying the pages for real (COPY_NONE). - A single object can be accessed with both strategies without conflicts.
Nowadays, the copy strategy is decided per-object, but I think the desired type of access to an object should also be considered. For instance, the operation generated by vm_copy should almost always use COPY_NONE, while vm_map, when doing things such as providing a private map, should use COPY_DELAY. I'm testing a patch which does this distinction. I'll post the results.
