Re: [PATCH 08/12] gup: Don't allow FOLL_LONGTERM pinning of FS DAX pages

[Dan Williams <dan.j.williams@intel.com>]

Alistair Popple wrote:
> Longterm pinning of FS DAX pages should already be disallowed by
> various pXX_devmap checks. However a future change will cause these
> checks to be invalid for FS DAX pages so make
> folio_is_longterm_pinnable() return false for FS DAX pages.
> 
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> ---
>  include/linux/memremap.h | 11 +++++++++++
>  include/linux/mm.h       |  4 ++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 14273e6..6a1406a 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -187,6 +187,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
>  	return is_device_coherent_page(&folio->page);
>  }
>  
> +static inline bool is_device_dax_page(const struct page *page)
> +{
> +	return is_zone_device_page(page) &&
> +		page_dev_pagemap(page)->type == MEMORY_DEVICE_FS_DAX;
> +}
> +
> +static inline bool folio_is_device_dax(const struct folio *folio)
> +{
> +	return is_device_dax_page(&folio->page);
> +}
> +
>  #ifdef CONFIG_ZONE_DEVICE
>  void zone_device_page_init(struct page *page);
>  void *memremap_pages(struct dev_pagemap *pgmap, int nid);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ae6d713..935e493 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1989,6 +1989,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>  	if (folio_is_device_coherent(folio))
>  		return false;
>  
> +	/* DAX must also always allow eviction. */
> +	if (folio_is_device_dax(folio))

Why is this called "folio_is_device_dax()" when the check is for fsdax?

I would expect:

if (folio_is_fsdax(folio))
	return false;

...and s/device_dax/fsdax/ for the rest of the helpers.