[PATCH 04/12] mm: Allow compound zone device pages

[Matthew Wilcox]

On Tue, Sep 10, 2024 at 02:14:29PM +1000, Alistair Popple wrote:
> @@ -337,6 +341,7 @@ struct folio {
>  	/* private: */
>  				};
>  	/* public: */
> +			struct dev_pagemap *pgmap;

Shouldn't that be indented by one more tab stop?

And for ease of reading, perhaps it should be placed either immediately
before or after 'struct list_head lru;'?

> +++ b/include/linux/mmzone.h
> @@ -1134,6 +1134,12 @@ static inline bool is_zone_device_page(const struct page *page)
>  	return page_zonenum(page) == ZONE_DEVICE;
>  }
>  
> +static inline struct dev_pagemap *page_dev_pagemap(const struct page *page)
> +{
> +	WARN_ON(!is_zone_device_page(page));
> +	return page_folio(page)->pgmap;
> +}

I haven't read to the end yet, but presumably we'll eventually want:

static inline struct dev_pagemap *folio_dev_pagemap(const struct folio *folio)
{
	WARN_ON(!folio_is_zone_device(folio))
	return folio->pgmap;
}

and since we'll want it eventually, maybe now is the time to add it,
and make page_dev_pagemap() simply call it?