Re: [PATCH 1/2] mm/gup: Remove dead pgmap refcounting code

[Alistair Popple <apopple@nvidia.com>]

On 2025-09-02 at 22:06 +1000, Jason Gunthorpe <jgg@ziepe.ca> wrote...
> On Tue, Sep 02, 2025 at 03:14:20PM +1000, Alistair Popple wrote:
> > Prior to aed877c2b425 ("device/dax: properly refcount device dax pages
> > when mapping") ZONE_DEVICE pages were not fully reference counted when
> > mapped into user page tables. Instead GUP would take a reference on the
> > associated pgmap to ensure the results of pfn_to_page() remained valid.
> > 
> > This is no longer required and most of the code was removed by
> > fd2825b0760a ("mm/gup: remove pXX_devmap usage from get_user_pages()").
> > Finish cleaning this up by removing the dead calls to put_dev_pagemap()
> > and the temporary context struct.
> > 
> > Signed-off-by: Alistair Popple <apopple@nvidia.com>
> > ---
> >  mm/gup.c | 67 ++++++++++++++++++++++----------------------------------
> >  1 file changed, 26 insertions(+), 41 deletions(-)
> 
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> 
> Yay! This never made alot of sense :\

Yeah. We could probably get rid of the pagemap refcounting entirely, but that's
on my backlog for now as it doesn't seem super important.

> Jason