[PATCH v3 01/10] mm: Add pfn_swap_entry_folio()

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Thanks to the compound_head() hidden inside PageLocked(), this saves a
call to compound_head() over calling page_folio(pfn_swap_entry_to_page())

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/swapops.h | 13 +++++++++++++
 mm/filemap.c            |  2 +-
 mm/huge_memory.c        |  2 +-
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index bff1e8d97de0..48b700ba1d18 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -468,6 +468,19 @@ static inline struct page *pfn_swap_entry_to_page(swp_entry_t entry)
 	return p;
 }
 
+static inline struct folio *pfn_swap_entry_folio(swp_entry_t entry)
+{
+	struct folio *folio = pfn_folio(swp_offset_pfn(entry));
+
+	/*
+	 * Any use of migration entries may only occur while the
+	 * corresponding folio is locked
+	 */
+	BUG_ON(is_migration_entry(entry) && !folio_test_locked(folio));
+
+	return folio;
+}
+
 /*
  * A pfn swap entry is a special type of swap entry that always has a pfn stored
  * in the swap offset. They are used to represent unaddressable device memory
diff --git a/mm/filemap.c b/mm/filemap.c
index 750e779c23db..c704085f29b6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1354,7 +1354,7 @@ void migration_entry_wait_on_locked(swp_entry_t entry, spinlock_t *ptl)
 	unsigned long pflags;
 	bool in_thrashing;
 	wait_queue_head_t *q;
-	struct folio *folio = page_folio(pfn_swap_entry_to_page(entry));
+	struct folio *folio = pfn_swap_entry_folio(entry);
 
 	q = folio_waitqueue(folio);
 	if (!folio_test_uptodate(folio) && folio_test_workingset(folio)) {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 94ef5c02b459..5b2da360ae0c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2035,7 +2035,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 	if (is_swap_pmd(*pmd)) {
 		swp_entry_t entry = pmd_to_swp_entry(*pmd);
-		struct folio *folio = page_folio(pfn_swap_entry_to_page(entry));
+		struct folio *folio = pfn_swap_entry_folio(entry);
 		pmd_t newpmd;
 
 		VM_BUG_ON(!is_pmd_migration_entry(*pmd));
-- 
2.43.0