LinuxKPI: replace vtophys+PHYS_TO_VM_PAGE with virt_to_page

[bz]

Summary

Rather than using the FreeBSD internal calls vtophys() and
PHYS_TO_VM_PAGE() use the already existing LinuxKPI abstraction for
this called virt_to_page(). This reduces the amount of compat code
to maintain and will allow further work on struct [vm_]page.

This should be a NOP.

Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks

[markj]

I have no objection to this and it looks ok, but I don't really understand it. Why is it useful to use Linux interfaces in these internal routines which deal with vm_page_t's and FreeBSD VM interfaces?

[bz]

In D41257#939742, @markj wrote:

I have no objection to this and it looks ok, but I don't really understand it. Why is it useful to use Linux interfaces in these internal routines which deal with vm_page_t's and FreeBSD VM interfaces?

Because after D41255 linux_alloc_pages and linux_free_pages properly return/take a 'struct page *'. For as long as they are aliased by the #define page vm_page that's fine; once that alias goes away a struct page will be a struct page and a struct vm_page will be a struct vm_page and the less places we'll have to deal with to get from one to the other for internal handling the better this will be.