I would like to use it in the page daemon. In particular, we might in
principle have code that sets PGA_REQUEUE or PGA_DEQUEUE without
creating a batch entry for the page. Upon encountering such a page, the
page daemon should create the batch entry. Today it does that
indirectly; for example, the laundry thread will call vm_page_requeue()
if the page has PGA_REQUEUE set. But vm_page_requeue() tests for and
sets PGA_REQUEUE, which is redundant in this case, and I would like
a way to create a batch entry for a page without modifying that page
at all, so as to handle the possibility that the page is concurrently
being freed.
For consistency in the vm_page.h namespace, rename it to
vm_page_pqbatch_submit(). Also for consistency, rename
vm_page_drain_pqbatch() to vm_page_pqbatch_drain().