Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down

[David Howells <dhowells@xxxxxxxxxx>]

Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:

> if (cleanup_flags & PAGE_CLEANUP_UNPIN)
>    gup_put_folio(folio, 1, true);
> else if (cleanup_flags & PAGE_CLEANUP_PUT)
>    gup_put_folio(folio, 1, false);

gup_put_folio() doesn't take a bool - it takes FOLL_PIN and FOLL_GET:

static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)

though I could do:

	if (cleanup_flags & PAGE_CLEANUP_UNPIN)
		gup_put_folio(folio, 1, FOLL_PIN);
	else if (cleanup_flags & PAGE_CLEANUP_PUT)
		gup_put_folio(folio, 1, FOLL_GET);

But the reason I wrote it like this:

 		gup_flags |= cleanup_flags & PAGE_CLEANUP_UNPIN ? FOLL_PIN : 0;
 		gup_flags |= cleanup_flags & PAGE_CLEANUP_PUT ? FOLL_GET : 0;

is that if PAGE_CLEANUP_UNPIN == FOLL_PIN and PAGE_CLEANUP_PUT == FOLL_GET,
the C compiler optimiser should be able to turn all of that into a single AND
instruction.

David