[PATCH RFC 11/11] mm/migrate: pass migrate_control to migrate_folio()

[Shivank Garg]

The migration core now carries policy in struct migrate_control, but
migrate_folio() and the address_space migrate_folio callback still receive
only the migration mode. This prevents additional policy, such as
copy-cache hints, from reaching folio-specific migration code.

Pass the control as const through migrate_folio(), the common migration
helpers, and the address_space callback. Update all implementations and
documentation accordingly. Existing callbacks continue to make their
decisions from ctl->mode only, none changes behavior yet.

No functional change intended.

Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
---
 Documentation/filesystems/locking.rst |  2 +-
 Documentation/filesystems/vfs.rst     |  7 +++--
 fs/aio.c                              |  2 +-
 fs/btrfs/disk-io.c                    |  5 ++--
 fs/btrfs/inode.c                      |  6 ++---
 fs/hugetlbfs/inode.c                  |  4 +--
 fs/jfs/jfs_metapage.c                 | 14 +++++-----
 fs/nfs/internal.h                     |  2 +-
 fs/nfs/write.c                        |  8 +++---
 include/linux/buffer_head.h           |  6 +++--
 include/linux/fs.h                    |  6 ++---
 include/linux/migrate.h               |  2 +-
 include/linux/pagemap.h               |  2 +-
 mm/migrate.c                          | 50 +++++++++++++++++++----------------
 mm/secretmem.c                        |  3 ++-
 virt/kvm/guest_memfd.c                |  2 +-
 16 files changed, 66 insertions(+), 55 deletions(-)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 844d65eb47a5..b406df403b4a 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -260,7 +260,7 @@ prototypes::
 	void (*free_folio)(struct folio *);
 	int (*direct_IO)(struct kiocb *, struct iov_iter *iter);
 	int (*migrate_folio)(struct address_space *, struct folio *dst,
-			struct folio *src, enum migrate_mode);
+			struct folio *src, const struct migrate_control *ctl);
 	int (*launder_folio)(struct folio *);
 	bool (*is_partially_uptodate)(struct folio *, size_t from, size_t count);
 	int (*error_remove_folio)(struct address_space *, struct folio *);
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index d3a93eec3945..8e1404723db1 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -767,7 +767,8 @@ cache in your filesystem.  The following members are defined:
 		void (*free_folio)(struct folio *);
 		ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter);
 		int (*migrate_folio)(struct mapping *, struct folio *dst,
-				struct folio *src, enum migrate_mode);
+				struct folio *src,
+				const struct migrate_control *ctl);
 		int (*launder_folio) (struct folio *);
 
 		bool (*is_partially_uptodate) (struct folio *, size_t from,
@@ -939,7 +940,9 @@ cache in your filesystem.  The following members are defined:
 	wants to relocate a folio (maybe from a memory device that is
 	signalling imminent failure) it will pass a new folio and an old
 	folio to this function.  migrate_folio should transfer any private
-	data across and update any references that it has to the folio.
+	data across and update any references that it has to the folio.  The
+	control describes the blocking mode and the reason for migration.  If
+	the mode is ``MIGRATE_ASYNC``, the callback must not block.
 
 ``launder_folio``
 	Called before freeing a folio - it writes back the dirty folio.
diff --git a/fs/aio.c b/fs/aio.c
index d78acc69f487..58ee9d0845dd 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -458,7 +458,7 @@ static const struct file_operations aio_ring_fops = {
 
 #if IS_ENABLED(CONFIG_MIGRATION)
 static int aio_migrate_folio(struct address_space *mapping, struct folio *dst,
-			struct folio *src, enum migrate_mode mode)
+			     struct folio *src, const struct migrate_control *ctl)
 {
 	struct kioctx *ctx;
 	struct aio_inode_info *ai = AIO_I(mapping->host);
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 819727460bcf..509651577a1c 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -460,7 +460,8 @@ int btrfs_validate_extent_buffer(struct extent_buffer *eb,
 
 #ifdef CONFIG_MIGRATION
 static int btree_migrate_folio(struct address_space *mapping,
-		struct folio *dst, struct folio *src, enum migrate_mode mode)
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *ctl)
 {
 	/*
 	 * we can't safely write a btree page from here,
@@ -475,7 +476,7 @@ static int btree_migrate_folio(struct address_space *mapping,
 	if (folio_get_private(src) &&
 	    !filemap_release_folio(src, GFP_KERNEL))
 		return -EAGAIN;
-	return migrate_folio(mapping, dst, src, mode);
+	return migrate_folio(mapping, dst, src, ctl);
 }
 #else
 #define btree_migrate_folio NULL
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3c10a0ef0002..9f1e567fa5ed 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7653,10 +7653,10 @@ static bool btrfs_release_folio(struct folio *folio, gfp_t gfp_flags)
 
 #ifdef CONFIG_MIGRATION
 static int btrfs_migrate_folio(struct address_space *mapping,
-			     struct folio *dst, struct folio *src,
-			     enum migrate_mode mode)
+			       struct folio *dst, struct folio *src,
+			       const struct migrate_control *ctl)
 {
-	int ret = filemap_migrate_folio(mapping, dst, src, mode);
+	int ret = filemap_migrate_folio(mapping, dst, src, ctl);
 
 	if (ret)
 		return ret;
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 7611a8470ea2..367148251689 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -1022,8 +1022,8 @@ static int hugetlbfs_symlink(struct mnt_idmap *idmap,
 
 #ifdef CONFIG_MIGRATION
 static int hugetlbfs_migrate_folio(struct address_space *mapping,
-				struct folio *dst, struct folio *src,
-				enum migrate_mode mode)
+				   struct folio *dst, struct folio *src,
+				   const struct migrate_control *ctl)
 {
 	int rc;
 
diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index 41fe12e641ce..7958edacb497 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -155,7 +155,7 @@ static inline void dec_io(struct folio *folio, blk_status_t status,
 #ifdef CONFIG_MIGRATION
 static int __metapage_migrate_folio(struct address_space *mapping,
 				    struct folio *dst, struct folio *src,
-				    enum migrate_mode mode)
+				    const struct migrate_control *ctl)
 {
 	struct meta_anchor *src_anchor = src->private;
 	struct metapage *mps[MPS_PER_PAGE] = {0};
@@ -168,7 +168,7 @@ static int __metapage_migrate_folio(struct address_space *mapping,
 			return -EAGAIN;
 	}
 
-	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	rc = filemap_migrate_folio(mapping, dst, src, ctl);
 	if (rc)
 		return rc;
 
@@ -231,7 +231,7 @@ static inline void remove_metapage(struct folio *folio, struct metapage *mp)
 #ifdef CONFIG_MIGRATION
 static int __metapage_migrate_folio(struct address_space *mapping,
 				    struct folio *dst, struct folio *src,
-				    enum migrate_mode mode)
+				    const struct migrate_control *ctl)
 {
 	struct metapage *mp;
 	int page_offset;
@@ -241,7 +241,7 @@ static int __metapage_migrate_folio(struct address_space *mapping,
 	if (metapage_locked(mp))
 		return -EAGAIN;
 
-	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	rc = filemap_migrate_folio(mapping, dst, src, ctl);
 	if (rc)
 		return rc;
 
@@ -645,18 +645,18 @@ static bool metapage_release_folio(struct folio *folio, gfp_t gfp_mask)
  */
 static int metapage_migrate_folio(struct address_space *mapping,
 				  struct folio *dst, struct folio *src,
-				  enum migrate_mode mode)
+				  const struct migrate_control *ctl)
 {
 	int expected_count;
 
 	if (!src->private)
-		return filemap_migrate_folio(mapping, dst, src, mode);
+		return filemap_migrate_folio(mapping, dst, src, ctl);
 
 	/* Check whether page does not have extra refs before we do more work */
 	expected_count = folio_expected_ref_count(src) + 1;
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
-	return __metapage_migrate_folio(mapping, dst, src, mode);
+	return __metapage_migrate_folio(mapping, dst, src, ctl);
 }
 #else
 #define metapage_migrate_folio NULL
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index abc81f5ae578..e1f366cff2c0 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -673,7 +673,7 @@ void nfs_clear_pnfs_ds_commit_verifiers(struct pnfs_ds_commit_info *cinfo)
 
 #ifdef CONFIG_MIGRATION
 int nfs_migrate_folio(struct address_space *, struct folio *dst,
-		struct folio *src, enum migrate_mode);
+		struct folio *src, const struct migrate_control *);
 #else
 #define nfs_migrate_folio NULL
 #endif
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 623e7ef1f73d..159135900399 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -2112,7 +2112,7 @@ int nfs_wb_folio(struct inode *inode, struct folio *folio)
 
 #ifdef CONFIG_MIGRATION
 int nfs_migrate_folio(struct address_space *mapping, struct folio *dst,
-		struct folio *src, enum migrate_mode mode)
+		struct folio *src, const struct migrate_control *ctl)
 {
 	/*
 	 * If the private flag is set, the folio is currently associated with
@@ -2123,19 +2123,19 @@ int nfs_migrate_folio(struct address_space *mapping, struct folio *dst,
 	 *        the folio lock.
 	 */
 	if (folio_test_private(src)) {
-		if (mode == MIGRATE_SYNC)
+		if (ctl->mode == MIGRATE_SYNC)
 			nfs_wb_folio(src->mapping->host, src);
 		if (folio_test_private(src))
 			return -EBUSY;
 	}
 
 	if (folio_test_private_2(src)) { /* [DEPRECATED] */
-		if (mode == MIGRATE_ASYNC)
+		if (ctl->mode == MIGRATE_ASYNC)
 			return -EBUSY;
 		folio_wait_private_2(src);
 	}
 
-	return migrate_folio(mapping, dst, src, mode);
+	return migrate_folio(mapping, dst, src, ctl);
 }
 #endif
 
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index fd2c7115c054..e4476596c9b6 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -277,9 +277,11 @@ int block_truncate_page(struct address_space *, loff_t, get_block_t *);
 
 #ifdef CONFIG_MIGRATION
 extern int buffer_migrate_folio(struct address_space *,
-		struct folio *dst, struct folio *src, enum migrate_mode);
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *);
 extern int buffer_migrate_folio_norefs(struct address_space *,
-		struct folio *dst, struct folio *src, enum migrate_mode);
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *);
 #else
 #define buffer_migrate_folio NULL
 #define buffer_migrate_folio_norefs NULL
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f9d1e05e8ae6..93ba6054c478 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -423,11 +423,11 @@ struct address_space_operations {
 	void (*free_folio)(struct folio *folio);
 	ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter);
 	/*
-	 * migrate the contents of a folio to the specified target. If
-	 * migrate_mode is MIGRATE_ASYNC, it must not block.
+	 * Migrate the contents of a folio to the specified target.  The
+	 * callback must not block when ctl->mode is MIGRATE_ASYNC.
 	 */
 	int (*migrate_folio)(struct address_space *, struct folio *dst,
-			struct folio *src, enum migrate_mode);
+			struct folio *src, const struct migrate_control *ctl);
 	int (*launder_folio)(struct folio *);
 	bool (*is_partially_uptodate) (struct folio *, size_t from,
 			size_t count);
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index cec5713944e3..123111e7abd3 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -55,7 +55,7 @@ extern const char *migrate_reason_names[MR_TYPES];
 
 void putback_movable_pages(struct list_head *l);
 int migrate_folio(struct address_space *mapping, struct folio *dst,
-		struct folio *src, enum migrate_mode mode);
+		struct folio *src, const struct migrate_control *ctl);
 int migrate_pages(struct list_head *l, new_folio_t new, free_folio_t free,
 		unsigned long private, const struct migrate_control *ctl,
 		unsigned int *ret_succeeded);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 0adfa6605653..455d57307f88 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1327,7 +1327,7 @@ bool noop_dirty_folio(struct address_space *mapping, struct folio *folio);
 
 #ifdef CONFIG_MIGRATION
 int filemap_migrate_folio(struct address_space *mapping, struct folio *dst,
-		struct folio *src, enum migrate_mode mode);
+		struct folio *src, const struct migrate_control *ctl);
 #else
 #define filemap_migrate_folio NULL
 #endif
diff --git a/mm/migrate.c b/mm/migrate.c
index 549f8b57092c..731836664a86 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -869,7 +869,7 @@ EXPORT_SYMBOL(folio_migrate_flags);
 
 static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 			   struct folio *src, void *src_private,
-			   enum migrate_mode mode)
+			   const struct migrate_control *ctl)
 {
 	int rc, expected_count = folio_expected_ref_count(src) + 1;
 
@@ -897,7 +897,7 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
  * @mapping: The address_space containing the folio.
  * @dst: The folio to migrate the data to.
  * @src: The folio containing the current data.
- * @mode: How to migrate the folio.
+ * @ctl: Migration policy for this folio.
  *
  * Common logic to directly migrate a single LRU folio suitable for
  * folios that do not have private data.
@@ -905,10 +905,10 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
  * Folios are locked upon entry and exit.
  */
 int migrate_folio(struct address_space *mapping, struct folio *dst,
-		  struct folio *src, enum migrate_mode mode)
+		  struct folio *src, const struct migrate_control *ctl)
 {
 	BUG_ON(folio_test_writeback(src));	/* Writeback must be complete */
-	return __migrate_folio(mapping, dst, src, NULL, mode);
+	return __migrate_folio(mapping, dst, src, NULL, ctl);
 }
 EXPORT_SYMBOL(migrate_folio);
 
@@ -947,8 +947,8 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head,
 }
 
 static int __buffer_migrate_folio(struct address_space *mapping,
-		struct folio *dst, struct folio *src, enum migrate_mode mode,
-		bool check_refs)
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *ctl, bool check_refs)
 {
 	struct buffer_head *bh, *head;
 	int rc;
@@ -956,14 +956,14 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 
 	head = folio_buffers(src);
 	if (!head)
-		return migrate_folio(mapping, dst, src, mode);
+		return migrate_folio(mapping, dst, src, ctl);
 
 	/* Check whether page does not have extra refs before we do more work */
 	expected_count = folio_expected_ref_count(src) + 1;
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
 
-	if (!buffer_migrate_lock_buffers(head, mode))
+	if (!buffer_migrate_lock_buffers(head, ctl->mode))
 		return -EAGAIN;
 
 	if (check_refs) {
@@ -995,7 +995,7 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 		}
 	}
 
-	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	rc = filemap_migrate_folio(mapping, dst, src, ctl);
 	if (rc)
 		goto unlock_buffers;
 
@@ -1022,7 +1022,7 @@ static int __buffer_migrate_folio(struct address_space *mapping,
  * @mapping: The address space containing @src.
  * @dst: The folio to migrate to.
  * @src: The folio to migrate from.
- * @mode: How to migrate the folio.
+ * @ctl: Migration policy for this folio.
  *
  * This function can only be used if the underlying filesystem guarantees
  * that no other references to @src exist. For example attached buffer
@@ -1033,9 +1033,10 @@ static int __buffer_migrate_folio(struct address_space *mapping,
  * Return: 0 on success or a negative errno on failure.
  */
 int buffer_migrate_folio(struct address_space *mapping,
-		struct folio *dst, struct folio *src, enum migrate_mode mode)
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *ctl)
 {
-	return __buffer_migrate_folio(mapping, dst, src, mode, false);
+	return __buffer_migrate_folio(mapping, dst, src, ctl, false);
 }
 EXPORT_SYMBOL(buffer_migrate_folio);
 
@@ -1044,7 +1045,7 @@ EXPORT_SYMBOL(buffer_migrate_folio);
  * @mapping: The address space containing @src.
  * @dst: The folio to migrate to.
  * @src: The folio to migrate from.
- * @mode: How to migrate the folio.
+ * @ctl: Migration policy for this folio.
  *
  * Like buffer_migrate_folio() except that this variant is more careful
  * and checks that there are also no buffer head references. This function
@@ -1054,17 +1055,19 @@ EXPORT_SYMBOL(buffer_migrate_folio);
  * Return: 0 on success or a negative errno on failure.
  */
 int buffer_migrate_folio_norefs(struct address_space *mapping,
-		struct folio *dst, struct folio *src, enum migrate_mode mode)
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *ctl)
 {
-	return __buffer_migrate_folio(mapping, dst, src, mode, true);
+	return __buffer_migrate_folio(mapping, dst, src, ctl, true);
 }
 EXPORT_SYMBOL_GPL(buffer_migrate_folio_norefs);
 #endif /* CONFIG_BUFFER_HEAD */
 
 int filemap_migrate_folio(struct address_space *mapping,
-		struct folio *dst, struct folio *src, enum migrate_mode mode)
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *ctl)
 {
-	return __migrate_folio(mapping, dst, src, folio_get_private(src), mode);
+	return __migrate_folio(mapping, dst, src, folio_get_private(src), ctl);
 }
 EXPORT_SYMBOL_GPL(filemap_migrate_folio);
 
@@ -1072,7 +1075,8 @@ EXPORT_SYMBOL_GPL(filemap_migrate_folio);
  * Default handling if a filesystem does not provide a migration function.
  */
 static int fallback_migrate_folio(struct address_space *mapping,
-		struct folio *dst, struct folio *src, enum migrate_mode mode)
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *ctl)
 {
 	WARN_ONCE(mapping->a_ops->writepages,
 			"%ps does not implement migrate_folio\n",
@@ -1085,9 +1089,9 @@ static int fallback_migrate_folio(struct address_space *mapping,
 	 * can't migrate automatically.
 	 */
 	if (!filemap_release_folio(src, GFP_KERNEL))
-		return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY;
+		return ctl->mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY;
 
-	return migrate_folio(mapping, dst, src, mode);
+	return migrate_folio(mapping, dst, src, ctl);
 }
 
 /*
@@ -1112,7 +1116,7 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
 	VM_BUG_ON_FOLIO(!folio_test_locked(dst), dst);
 
 	if (!mapping)
-		rc = migrate_folio(mapping, dst, src, ctl->mode);
+		rc = migrate_folio(mapping, dst, src, ctl);
 	else if (mapping_inaccessible(mapping))
 		rc = -EOPNOTSUPP;
 	else if (mapping->a_ops->migrate_folio)
@@ -1123,9 +1127,9 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
 		 * migrate_folio callback. This is the most common path
 		 * for page migration.
 		 */
-		rc = mapping->a_ops->migrate_folio(mapping, dst, src, ctl->mode);
+		rc = mapping->a_ops->migrate_folio(mapping, dst, src, ctl);
 	else
-		rc = fallback_migrate_folio(mapping, dst, src, ctl->mode);
+		rc = fallback_migrate_folio(mapping, dst, src, ctl);
 
 	if (!rc) {
 		/*
diff --git a/mm/secretmem.c b/mm/secretmem.c
index d29865075b6e..5c81833981d2 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -144,7 +144,8 @@ static const struct file_operations secretmem_fops = {
 };
 
 static int secretmem_migrate_folio(struct address_space *mapping,
-		struct folio *dst, struct folio *src, enum migrate_mode mode)
+		struct folio *dst, struct folio *src,
+		const struct migrate_control *ctl)
 {
 	return -EBUSY;
 }
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 625e62e1a031..0a9af8c4768d 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -457,7 +457,7 @@ static struct file_operations kvm_gmem_fops = {
 
 static int kvm_gmem_migrate_folio(struct address_space *mapping,
 				  struct folio *dst, struct folio *src,
-				  enum migrate_mode mode)
+				  const struct migrate_control *ctl)
 {
 	WARN_ON_ONCE(1);
 	return -EINVAL;

-- 
2.43.0