Remove now-unneeded page zeroing. No functional change intended.
The variable becomes somewhat pointless. You can directly pass _WIRED|_ALLOC_ZERO to vm_page_alloc_noobj_contig(), and vm_page_reclaim_contig() is fine with 0 instead pflags.
Is PAGE_SIZE actually correct? I would guess that Linux guarantees that an order n allocation is aligned to an order n address. That said, at the moment, this is probably not an issue because of the way that vm_phys does contig allocations.
Does VM_ALLOC_ZERO actually make sense here?
I can't find any Linux documentation or code that definitively answers this. Looking at the alloc_pages() implementation, it does seem to return self-aligned runs in practice, but I can't tell if this is a guarantee of the interface. alloc_contig_pages() has a comment stating that self-alignment is guaranteed if the size of the run is a power of 2, but this function is not used much.