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SubjectRe: [PATCH 2/2] mm/gup: frame_vector: convert get_user_pages() --> pin_user_pages()
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On 28.05.20 00:32, John Hubbard wrote:
> This code was using get_user_pages*(), and all of the callers so far
> were in a "Case 2" scenario (DMA/RDMA), using the categorization
> from [1]. That means that it's time to convert the get_user_pages*() +
> put_page() calls to pin_user_pages*() + unpin_user_pages() calls.
>
> There is some helpful background in [2]: basically, this is a small
> part of fixing a long-standing disconnect between pinning pages, and
> file systems' use of those pages.
>
> [1] Documentation/core-api/pin_user_pages.rst
>
> [2] "Explicit pinning of user-space pages":
> https://lwn.net/Articles/807108/
>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
> mm/frame_vector.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> index c431ca81dad5..4107dbca0056 100644
> --- a/mm/frame_vector.c
> +++ b/mm/frame_vector.c
> @@ -72,7 +72,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> vec->got_ref = true;
> vec->is_pfns = false;
> - ret = get_user_pages_locked(start, nr_frames,
> + ret = pin_user_pages_locked(start, nr_frames,
> gup_flags, (struct page **)(vec->ptrs), &locked);
> goto out;
> }
> @@ -122,7 +122,6 @@ EXPORT_SYMBOL(get_vaddr_frames);
> */
> void put_vaddr_frames(struct frame_vector *vec)
> {
> - int i;
> struct page **pages;
>
> if (!vec->got_ref)
> @@ -135,8 +134,8 @@ void put_vaddr_frames(struct frame_vector *vec)
> */
> if (WARN_ON(IS_ERR(pages)))
> goto out;
> - for (i = 0; i < vec->nr_frames; i++)
> - put_page(pages[i]);
> +
> + unpin_user_pages(pages, vec->nr_frames);
> vec->got_ref = false;
> out:
> vec->nr_frames = 0;
>

Not familiar with this code, but from what I can tell this LGTM.

--
Thanks,

David / dhildenb

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