Re: [PATCH v2 1/3] mm/gup: Introduce pin_user_pages_fd() for pinning shmem/hugetlbfs file pages (v2)

[Jason Gunthorpe <jgg@nvidia.com>]

On Sun, Nov 05, 2023 at 10:15:39PM -0800, Vivek Kasireddy wrote:
> For drivers that would like to longterm-pin the pages associated
> with a file, the pin_user_pages_fd() API provides an option to
> not only pin the pages via FOLL_PIN but also to check and migrate
> them if they reside in movable zone or CMA block. This API
> currently works with files that belong to either shmem or hugetlbfs.
> Files belonging to other filesystems are rejected for now.
> 
> The pages need to be located first before pinning them via FOLL_PIN.
> If they are found in the page cache, they can be immediately pinned.
> Otherwise, they need to be allocated using the filesystem specific
> APIs and then pinned.
> 
> v2:
> - Drop gup_flags and improve comments and commit message (David)
> - Allocate a page if we cannot find in page cache for the hugetlbfs
>   case as well (David)
> - Don't unpin pages if there is a migration related failure (David)
> - Drop the unnecessary nr_pages <= 0 check (Jason)
> - Have the caller of the API pass in file * instead of fd (Jason)
> 
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Dongwon Kim <dongwon.kim@intel.com>
> Cc: Junxiao Chang <junxiao.chang@intel.com>
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>  include/linux/mm.h |  2 +
>  mm/gup.c           | 99 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 101 insertions(+)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason