Re: Extending page pinning into fs/direct-io.c

[Linus Torvalds]

On Thu, May 25, 2023 at 9:45 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> I think the correct way to test for a zero page is
> is_zero_pfn(page_to_pfn(page).

Yeah. Except it's really ugly and strange, and we should probably add
a helper for that pattern.

The reason it has that odd "look at pfn" is just because I think the
first users were in the page table code, which had the pfn already,
and the test is basically based on the zero_page_mask thing that the
affected architectures have.

So I suspect we should add that

    is_zero_pfn(page_to_pfn(page))

as a helper inline function rather than write it out even more times
(that "is this 'struct page' a zero page" pattern already exists in
/proc and a few other places.

is_longterm_pinnable_page() already has it, so adding it as a helper
there in <linux/mm.h> is probably a good idea.

                Linus