Re: [PATCH V2] mm/gup: folio_split_user_page_pin

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Sep 27, 2024 at 05:44:52PM +0200, David Hildenbrand wrote:
> /**
>  * folio_try_add_pins() - add pins to an already-pinned folio
>  * @folio: the folio to add more pins to
>  *
>  * Try to add more pins to an already-pinned folio. The semantics
>  * of the pin (e.g., FOLL_WRITE) follow any existing pin and cannot
>  * be changed.
>  *
>  * This function is helpful when having obtained a pin on a large folio
>  * using memfd_pin_folios(), but wanting to logically unpin parts
>  * (e.g., individual pages) of the folio later, for example, using
>  * unpin_user_page_range_dirty_lock().
>  *
>  * This is not the right interface to initially pin a folio.
>  */
> int folio_try_add_pins(struct folio *folio, unsigned int pins)
> {
> 	VM_WARN_ON_ONCE(!folio_maybe_dma_pinned(folio));
> 
> 	return try_grab_folio(folio, pins, FOLL_PIN);
> }

That looks pretty good to me too

Thanks,
Jason