The timing results for 8-10 buildworlds, with and without this patch. Without:

Drop the vm_page_iter_free() parts committed elsewhere.

Add a panic when a page duplication is found. Match param names between definition and declaration.

Comments in vm_reserv.c need to be updated to reflect this change.

Define inline pctrie_setpop() to flip popmap bits from 0 to 1 and assert that they have become set. Use it in 3 places.

Remove changes to vm_page_iter_remove.

Pass the removed page to vm_page_iter_remove, and functions that use it. Update comments. Reorder declarations.

Apply suggestions from feedback on D46724 to improve performance.

Drop the fix that @kib has committed separately.

Drop length argument to cdev_mgtdev_pager_free_pages().

Fix typo in tegra_bo.c.

Use vm_radix_iter_found in swap_pager.c. Tweak the pctrie.h implement to avoid a pointless null check.

Avoid the object != NULL check in vm_page_iter_free.

alc update 11/16.

Drop the bool argument from vm_page_free_toq. Turn vm_page_free_toq into a wrapper for the real implementation function, to which it passes 'true' as the bool argument.

Update some comments.

Remove changes to subr_pctrie.c. Pass the iterator to vm_page_rename() to allow the page to be removed with the iterator and the appropriate page number.

Rename vm_page_object_remove.

Rearrange into vm_page_iter_remove and vm_page_iter_free iter-based substitutes for the iter-less equivalents.

Performance test:
Ran 12 buildworlds, without and with this change, on an amd64 machine to verify it did not harm performance there.
Without:

Rebase. Undo some function reordering that makes this reviewer easier, even if it preserves some odd ordering.

Rebase.

Refresh.

If you're inserting batch [a,b,...,y.z], and if you began by inserting a and z with normal iter-insert, then your BATCH_SPLIT case would never happen and some of the complexity of batch_insert could be reduced. True or false?

In D47036, I put it after vm_radix_iter_step, mostly because PCTRIE_ITER_LOOKUP_LE comes shortly after PCTRIE_ITER_STEP_GE in pctrie.h. 'step' and 'jump' are built on top of lookup_ge, so I kept them grouped with lookup_ge.

Rebase.

Tweak the first loop in pctrie_iter_lookup_le to make it 2 whole bytes smaller. And, for the _ge version, one byte smaller.

Drop ..._iter_lookup_lt().

Jenkins says:
sys/fs/tmpfs/times_test:holey -> panic: Lock vmobject not exclusively locked @ /usr/src/sys/vm/swap_pager.c:2490