Re: [PATCH v3 1/7] iov_iter: Introduce fault_in_iov_iter helper

From: Linus Torvalds
Date: Mon Jul 26 2021 - 13:27:33 EST

On Mon, Jul 26, 2021 at 9:33 AM Jan Kara <jack@xxxxxxx> wrote:
> On Fri 23-07-21 22:58:34, Andreas Gruenbacher wrote:
> > + gup_flags = FOLL_TOUCH | FOLL_POPULATE;
> I don't think FOLL_POPULATE makes sense here. It makes sense only with
> FOLL_MLOCK and determines whether mlock(2) should fault in missing pages or
> not.

Yeah, it won't hurt, but FOLL_POPULATE doesn't actually do anything
unless FOLL_MLOCK is set. It is, as you say, a magic flag just for

The only ones that should matter are FOLL_WRITE (for obvious reasons)
and FOLL_TOUCH (to set the accessed and dirty bits, rather than just
th protection bits)