Re: [PATCH] mm/gup: documentation fix for pin_user_pages*() APIs

[David Hildenbrand <david@redhat.com>]

On 29.05.20 10:45, John Hubbard wrote:
> All of the pin_user_pages*() API calls will cause pages to be
> dma-pinned. As such, they are all suitable for either DMA, RDMA,
> and/or Direct IO. The documentation should say so, but it was
> instead saying that three of the API calls were only suitable for
> Direct IO. This was discovered when a reviewer wondered why an
> API call that specifically recommended against Case 2 (DMA/RDMA)
> was being used in a DMA situation [1].
> 
> Fix this by simply deleting those claims. The gup.c comments already
> refer to the more extensive Documentation/core-api/pin_user_pages.rst,
> which does have the correct guidance. So let's just write it once,
> there.
> 
> [1] https://lore.kernel.org/r/20200529074658.GM30374@kadam
> 
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
> 
> Hi,
> 
> This applies on top of linux-next, in order to avoid a conflict with
> Mauro Carvalho Chehab's fix to the lines right above these.
> 
> thanks,
> John Hubbard
> NVIDIA
> 
> 
>  mm/gup.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index ee039d421746d..311d0f11b35e6 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2875,9 +2875,6 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast);
>   *
>   * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
>   * see Documentation/core-api/pin_user_pages.rst for further details.
> - *
> - * This is intended for Case 1 (DIO) in Documentation/core-api/pin_user_pages.rst. It
> - * is NOT intended for Case 2 (RDMA: long-term pins).
>   */
>  int pin_user_pages_fast(unsigned long start, int nr_pages,
>  			unsigned int gup_flags, struct page **pages)
> @@ -2951,9 +2948,6 @@ EXPORT_SYMBOL_GPL(pin_user_pages_fast_only);
>   *
>   * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
>   * see Documentation/core-api/pin_user_pages.rst for details.
> - *
> - * This is intended for Case 1 (DIO) in Documentation/core-api/pin_user_pages.rst. It
> - * is NOT intended for Case 2 (RDMA: long-term pins).
>   */
>  long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
>  			   unsigned long start, unsigned long nr_pages,
> @@ -2987,9 +2981,6 @@ EXPORT_SYMBOL(pin_user_pages_remote);
>   *
>   * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
>   * see Documentation/core-api/pin_user_pages.rst for details.
> - *
> - * This is intended for Case 1 (DIO) in Documentation/core-api/pin_user_pages.rst. It
> - * is NOT intended for Case 2 (RDMA: long-term pins).
>   */
>  long pin_user_pages(unsigned long start, unsigned long nr_pages,
>  		    unsigned int gup_flags, struct page **pages,
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb