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

[Alistair Popple <apopple@nvidia.com>]

Matthew Wilcox <willy@infradead.org> writes:

> 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?

Sounds reasonable. I had open-coded folio->pgmap where it's needed
because at those points it's "obviously" a ZONE_DEVICE folio. Will add
it.