On Tue, Sep 10, 2024 at 04:57:41PM +1000, Alistair Popple wrote:

Matthew Wilcox [off-list ref] writes:

quoted

On Tue, Sep 10, 2024 at 02:14:29PM +1000, Alistair Popple wrote:

quoted

@@ -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;'?

quoted

+++ 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.

Oh, if it's obvious then just do the dereference.