Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down
From: David Howells
Date: Tue Jan 24 2023 - 09:13:02 EST
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