[PATCH v1 3/8] mm: Add helpers to create migration entries from struct pages

[Jordan Niethe <jniethe@nvidia.com>]

To create a new migration entry for a given struct page, that page is
first converted to its pfn, before passing the pfn to
make_readable_migration_entry() (and friends).

A future change will remove device private pages from the physical
address space. This will mean that device private pages no longer have a
pfn and must be handled separately.

Prepare for this with a new set of helpers:

  - make_readable_migration_entry_from_page()
  - make_readable_exclusive_migration_entry_from_page()
  - make_writable_migration_entry_from_page()

These helpers take a struct page as parameter instead of a pfn. This
will allow more flexibility for handling the swap offset field
differently for device private pages.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
---
v1:
  - New to series
---
 include/linux/swapops.h | 25 +++++++++++++++++++++++++
 mm/huge_memory.c        | 18 +++++++++---------
 mm/migrate_device.c     | 12 ++++++------
 mm/rmap.c               | 12 ++++++------
 4 files changed, 46 insertions(+), 21 deletions(-)

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 8cfc966eae48..72aa636fdb48 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -173,16 +173,31 @@ static inline swp_entry_t make_readable_migration_entry(pgoff_t offset)
 	return swp_entry(SWP_MIGRATION_READ, offset);
 }
 
+static inline swp_entry_t make_readable_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(SWP_MIGRATION_READ, page_to_pfn(page));
+}
+
 static inline swp_entry_t make_readable_exclusive_migration_entry(pgoff_t offset)
 {
 	return swp_entry(SWP_MIGRATION_READ_EXCLUSIVE, offset);
 }
 
+static inline swp_entry_t make_readable_exclusive_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(SWP_MIGRATION_READ_EXCLUSIVE, page_to_pfn(page));
+}
+
 static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
 {
 	return swp_entry(SWP_MIGRATION_WRITE, offset);
 }
 
+static inline swp_entry_t make_writable_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(SWP_MIGRATION_WRITE, page_to_pfn(page));
+}
+
 /*
  * Returns whether the host has large enough swap offset field to support
  * carrying over pgtable A/D bits for page migrations.  The result is
@@ -222,11 +237,21 @@ static inline swp_entry_t make_readable_migration_entry(pgoff_t offset)
 	return swp_entry(0, 0);
 }
 
+static inline swp_entry_t make_readable_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(0, 0);
+}
+
 static inline swp_entry_t make_readable_exclusive_migration_entry(pgoff_t offset)
 {
 	return swp_entry(0, 0);
 }
 
+static inline swp_entry_t make_readable_exclusive_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(0, 0);
+}
+
 static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
 {
 	return swp_entry(0, 0);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 40cf59301c21..08c68e2e3f06 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3183,14 +3183,14 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 
 		for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
 			if (write)
-				swp_entry = make_writable_migration_entry(
-							page_to_pfn(page + i));
+				swp_entry = make_writable_migration_entry_from_page(
+							page + i);
 			else if (anon_exclusive)
-				swp_entry = make_readable_exclusive_migration_entry(
-							page_to_pfn(page + i));
+				swp_entry = make_readable_exclusive_migration_entry_from_page(
+							page + i);
 			else
-				swp_entry = make_readable_migration_entry(
-							page_to_pfn(page + i));
+				swp_entry = make_readable_migration_entry_from_page(
+							page + i);
 			if (young)
 				swp_entry = make_migration_entry_young(swp_entry);
 			if (dirty)
@@ -4890,11 +4890,11 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
 	if (pmd_dirty(pmdval))
 		folio_mark_dirty(folio);
 	if (pmd_write(pmdval))
-		entry = make_writable_migration_entry(page_to_pfn(page));
+		entry = make_writable_migration_entry_from_page(page);
 	else if (anon_exclusive)
-		entry = make_readable_exclusive_migration_entry(page_to_pfn(page));
+		entry = make_readable_exclusive_migration_entry_from_page(page);
 	else
-		entry = make_readable_migration_entry(page_to_pfn(page));
+		entry = make_readable_migration_entry_from_page(page);
 	if (pmd_young(pmdval))
 		entry = make_migration_entry_young(entry);
 	if (pmd_dirty(pmdval))
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 5d108ddf1a97..7eef21d63364 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -438,14 +438,14 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 
 			/* Setup special migration page table entry */
 			if (mpfn & MIGRATE_PFN_WRITE)
-				entry = make_writable_migration_entry(
-							page_to_pfn(page));
+				entry = make_writable_migration_entry_from_page(
+							page);
 			else if (anon_exclusive)
-				entry = make_readable_exclusive_migration_entry(
-							page_to_pfn(page));
+				entry = make_readable_exclusive_migration_entry_from_page(
+							page);
 			else
-				entry = make_readable_migration_entry(
-							page_to_pfn(page));
+				entry = make_readable_migration_entry_from_page(
+							page);
 			if (pte_present(pte)) {
 				if (pte_young(pte))
 					entry = make_migration_entry_young(entry);
diff --git a/mm/rmap.c b/mm/rmap.c
index 79a2478b4aa9..bb881b0c4b06 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2539,14 +2539,14 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 			 * pte is removed and then restart fault handling.
 			 */
 			if (writable)
-				entry = make_writable_migration_entry(
-							page_to_pfn(subpage));
+				entry = make_writable_migration_entry_from_page(
+							subpage);
 			else if (anon_exclusive)
-				entry = make_readable_exclusive_migration_entry(
-							page_to_pfn(subpage));
+				entry = make_readable_exclusive_migration_entry_from_page(
+							subpage);
 			else
-				entry = make_readable_migration_entry(
-							page_to_pfn(subpage));
+				entry = make_readable_migration_entry_from_page(
+							subpage);
 			if (likely(pte_present(pteval))) {
 				if (pte_young(pteval))
 					entry = make_migration_entry_young(entry);
-- 
2.34.1