[RFC 01/11] mm/zone_device: support large zone device private folios

[Balbir Singh <balbirs@xxxxxxxxxx>]

Add routines to support allocation of large order zone device folios
and helper functions for zone device folios, to check if a folio is
device private and helpers for setting zone device data.

When large folios are used, the existing page_free() callback in
pgmap is called when the folio is freed, this is true for both
PAGE_SIZE and higher order pages.

Signed-off-by: Balbir Singh <balbirs@xxxxxxxxxx>
---
 include/linux/memremap.h | 22 +++++++++++++++++-
 mm/memremap.c            | 50 +++++++++++++++++++++++++++++-----------
 2 files changed, 58 insertions(+), 14 deletions(-)

diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 4aa151914eab..11d586dd8ef1 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -169,6 +169,18 @@ static inline bool folio_is_device_private(const struct folio *folio)
 	return is_device_private_page(&folio->page);
 }
 
+static inline void *folio_zone_device_data(const struct folio *folio)
+{
+	VM_BUG_ON_FOLIO(!folio_is_device_private(folio), folio);
+	return folio->page.zone_device_data;
+}
+
+static inline void folio_set_zone_device_data(struct folio *folio, void *data)
+{
+	VM_BUG_ON_FOLIO(!folio_is_device_private(folio), folio);
+	folio->page.zone_device_data = data;
+}
+
 static inline bool is_pci_p2pdma_page(const struct page *page)
 {
 	return IS_ENABLED(CONFIG_PCI_P2PDMA) &&
@@ -199,7 +211,7 @@ static inline bool folio_is_fsdax(const struct folio *folio)
 }
 
 #ifdef CONFIG_ZONE_DEVICE
-void zone_device_page_init(struct page *page);
+void init_zone_device_folio(struct folio *folio, unsigned int order);
 void *memremap_pages(struct dev_pagemap *pgmap, int nid);
 void memunmap_pages(struct dev_pagemap *pgmap);
 void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap);
@@ -209,6 +221,14 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
 bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn);
 
 unsigned long memremap_compat_align(void);
+
+static inline void zone_device_page_init(struct page *page)
+{
+	struct folio *folio = page_folio(page);
+
+	init_zone_device_folio(folio, 0);
+}
+
 #else
 static inline void *devm_memremap_pages(struct device *dev,
 		struct dev_pagemap *pgmap)
diff --git a/mm/memremap.c b/mm/memremap.c
index 2aebc1b192da..7d98d0a4c0cd 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -459,20 +459,21 @@ EXPORT_SYMBOL_GPL(get_dev_pagemap);
 void free_zone_device_folio(struct folio *folio)
 {
 	struct dev_pagemap *pgmap = folio->pgmap;
+	unsigned int nr = folio_nr_pages(folio);
+	int i;
+	bool anon = folio_test_anon(folio);
+	struct page *page = folio_page(folio, 0);
 
 	if (WARN_ON_ONCE(!pgmap))
 		return;
 
 	mem_cgroup_uncharge(folio);
 
-	/*
-	 * Note: we don't expect anonymous compound pages yet. Once supported
-	 * and we could PTE-map them similar to THP, we'd have to clear
-	 * PG_anon_exclusive on all tail pages.
-	 */
-	if (folio_test_anon(folio)) {
-		VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
-		__ClearPageAnonExclusive(folio_page(folio, 0));
+	WARN_ON_ONCE(folio_test_large(folio) && !anon);
+
+	for (i = 0; i < nr; i++) {
+		if (anon)
+			__ClearPageAnonExclusive(folio_page(folio, i));
 	}
 
 	/*
@@ -496,10 +497,19 @@ void free_zone_device_folio(struct folio *folio)
 
 	switch (pgmap->type) {
 	case MEMORY_DEVICE_PRIVATE:
+		if (folio_test_large(folio)) {
+			folio_unqueue_deferred_split(folio);
+
+			percpu_ref_put_many(&folio->pgmap->ref, nr - 1);
+		}
+		pgmap->ops->page_free(page);
+		put_dev_pagemap(pgmap);
+		page->mapping = NULL;
+		break;
 	case MEMORY_DEVICE_COHERENT:
 		if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->page_free))
 			break;
-		pgmap->ops->page_free(folio_page(folio, 0));
+		pgmap->ops->page_free(page);
 		put_dev_pagemap(pgmap);
 		break;
 
@@ -523,14 +533,28 @@ void free_zone_device_folio(struct folio *folio)
 	}
 }
 
-void zone_device_page_init(struct page *page)
+void init_zone_device_folio(struct folio *folio, unsigned int order)
 {
+	struct page *page = folio_page(folio, 0);
+
+	VM_BUG_ON(order > MAX_ORDER_NR_PAGES);
+
+	WARN_ON_ONCE(order && order != HPAGE_PMD_ORDER);
+
 	/*
 	 * Drivers shouldn't be allocating pages after calling
 	 * memunmap_pages().
 	 */
-	WARN_ON_ONCE(!percpu_ref_tryget_live(&page_pgmap(page)->ref));
-	set_page_count(page, 1);
+	WARN_ON_ONCE(!percpu_ref_tryget_many(&page_pgmap(page)->ref, 1 << order));
+	folio_set_count(folio, 1);
 	lock_page(page);
+
+	/*
+	 * Only PMD level migration is supported for THP migration
+	 */
+	if (order > 1) {
+		prep_compound_page(page, order);
+		folio_set_large_rmappable(folio);
+	}
 }
-EXPORT_SYMBOL_GPL(zone_device_page_init);
+EXPORT_SYMBOL_GPL(init_zone_device_folio);
-- 
2.48.1