Do not clear page flags in vm_page_pqbatch_submit().

[markj]

Summary

All existing callers guarantee that the page does not have a
pre-existing dequeue pending. Thus, if the page is dequeued before
pqbatch_submit() acquires the page queue lock, we do not need to do
anything since vm_page_dequeue_complete() takes care of clearing all
page queue state flags for us.

With this change, vm_page_pqbatch_submit() has the nice property that it
does not directly modify any fields in the page structure.

Test Plan

Peter is testing the change.

[dougm]

All existing callers guarantee that the page does not have a pre-existing dequeue pending.

Can you add a KASSERT to express that in the callee?

[markj]

In D21372#464992, @dougm wrote:

All existing callers guarantee that the page does not have a pre-existing dequeue pending.

Can you add a KASSERT to express that in the callee?

I don't think it's

In D21372#464992, @dougm wrote:

All existing callers guarantee that the page does not have a pre-existing dequeue pending.

Can you add a KASSERT to express that in the callee?

I don't think so. Some callers, like vm_page_dequeue_deferred(), request a dequeue by setting PGA_DEQUEUE. It is possible that a lingering batch queue entry will cause PGA_DEQUEUE to be concurrently cleared in vm_pqbatch_process_page() at any point before vm_page_pqbatch_submit() acquires the page queue lock. So I cannot think of any useful and non-racy assertions to add in place of the line I removed.