Re: [PATCH 6/8] mm/gup: make locked never NULL in the internal GUP functions

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Jan 23, 2023 at 12:35:28PM +0100, David Hildenbrand wrote:
> On 17.01.23 16:58, Jason Gunthorpe wrote:
> > Now that NULL locked doesn't have a special meaning we can just make it
> > non-NULL in all cases and remove the special tests.
> > 
> > get_user_pages() and pin_user_pages() can safely pass in a locked = 1
> > 
> > get_user_pages_remote) and pin_user_pages_remote() can swap in a local
> > variable for locked if NULL is passed.
> > 
> > Remove all the NULL checks.
> > 
> > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> > ---
> >   mm/gup.c | 30 ++++++++++++++++++++----------
> >   1 file changed, 20 insertions(+), 10 deletions(-)
> 
> ... doesn't really look like a real cleanup. Especially with the
> 
>  2 files changed, 20 insertions(+), 12 deletions(-)
> 
> on the previous patch and a new internal flag ....
> 
> What's the benefit?

There are all kinds of unnecessary branches on the faster paths,
inside loops, etc to check for NULL when all we really needed was a
single bit flag.

It isalos much clearer to understand that a FOLL flag changes the
behavior of how GUP works rather than some weirdo NULL argument.

Jason