mm/migrate: Add filemap_migrate_folio()

There is nothing iomap-specific about iomap_migratepage(), and it fits
a pattern used by several other filesystems, so move it to mm/migrate.c,
convert it to be filemap_migrate_folio() and convert the iomap filesystems
to use it.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

fs/gfs2/aops.c

@@ -774,7 +774,7 @@ static const struct address_space_operations gfs2_aops = {
 	.invalidate_folio = iomap_invalidate_folio,
 	.bmap = gfs2_bmap,
 	.direct_IO = noop_direct_IO,
-	.migratepage = iomap_migrate_page,
+	.migrate_folio = filemap_migrate_folio,
 	.is_partially_uptodate = iomap_is_partially_uptodate,
 	.error_remove_page = generic_error_remove_page,
 };

fs/iomap/buffered-io.c

@@ -489,31 +489,6 @@ void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len)
 }
 EXPORT_SYMBOL_GPL(iomap_invalidate_folio);
 
-#ifdef CONFIG_MIGRATION
-int
-iomap_migrate_page(struct address_space *mapping, struct page *newpage,
-		struct page *page, enum migrate_mode mode)
-{
-	struct folio *folio = page_folio(page);
-	struct folio *newfolio = page_folio(newpage);
-	int ret;
-
-	ret = folio_migrate_mapping(mapping, newfolio, folio, 0);
-	if (ret != MIGRATEPAGE_SUCCESS)
-		return ret;
-
-	if (folio_test_private(folio))
-		folio_attach_private(newfolio, folio_detach_private(folio));
-
-	if (mode != MIGRATE_SYNC_NO_COPY)
-		folio_migrate_copy(newfolio, folio);
-	else
-		folio_migrate_flags(newfolio, folio);
-	return MIGRATEPAGE_SUCCESS;
-}
-EXPORT_SYMBOL_GPL(iomap_migrate_page);
-#endif /* CONFIG_MIGRATION */
-
 static void
 iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
 {

fs/xfs/xfs_aops.c

@@ -570,7 +570,7 @@ const struct address_space_operations xfs_address_space_operations = {
 	.invalidate_folio	= iomap_invalidate_folio,
 	.bmap			= xfs_vm_bmap,
 	.direct_IO		= noop_direct_IO,
-	.migratepage		= iomap_migrate_page,
+	.migrate_folio		= filemap_migrate_folio,
 	.is_partially_uptodate  = iomap_is_partially_uptodate,
 	.error_remove_page	= generic_error_remove_page,
 	.swap_activate		= xfs_iomap_swapfile_activate,

fs/zonefs/super.c

@@ -271,7 +271,7 @@ static const struct address_space_operations zonefs_file_aops = {
 	.dirty_folio		= filemap_dirty_folio,
 	.release_folio		= iomap_release_folio,
 	.invalidate_folio	= iomap_invalidate_folio,
-	.migratepage		= iomap_migrate_page,
+	.migrate_folio		= filemap_migrate_folio,
 	.is_partially_uptodate	= iomap_is_partially_uptodate,
 	.error_remove_page	= generic_error_remove_page,
 	.direct_IO		= noop_direct_IO,

include/linux/iomap.h

@@ -231,12 +231,6 @@ void iomap_readahead(struct readahead_control *, const struct iomap_ops *ops);
 bool iomap_is_partially_uptodate(struct folio *, size_t from, size_t count);
 bool iomap_release_folio(struct folio *folio, gfp_t gfp_flags);
 void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len);
-#ifdef CONFIG_MIGRATION
-int iomap_migrate_page(struct address_space *mapping, struct page *newpage,
-		struct page *page, enum migrate_mode mode);
-#else
-#define iomap_migrate_page NULL
-#endif
 int iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len,
 		const struct iomap_ops *ops);
 int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,

include/linux/pagemap.h

@@ -1078,6 +1078,12 @@ static inline int __must_check write_one_page(struct page *page)
 int __set_page_dirty_nobuffers(struct page *page);
 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);
+#else
+#define filemap_migrate_folio NULL
+#endif
 void page_endio(struct page *page, bool is_write, int err);
 
 void folio_end_private_2(struct folio *folio);

mm/migrate.c

@@ -784,6 +784,26 @@ int buffer_migrate_folio_norefs(struct address_space *mapping,
 }
 #endif
 
+int filemap_migrate_folio(struct address_space *mapping,
+		struct folio *dst, struct folio *src, enum migrate_mode mode)
+{
+	int ret;
+
+	ret = folio_migrate_mapping(mapping, dst, src, 0);
+	if (ret != MIGRATEPAGE_SUCCESS)
+		return ret;
+
+	if (folio_get_private(src))
+		folio_attach_private(dst, folio_detach_private(src));
+
+	if (mode != MIGRATE_SYNC_NO_COPY)
+		folio_migrate_copy(dst, src);
+	else
+		folio_migrate_flags(dst, src);
+	return MIGRATEPAGE_SUCCESS;
+}
+EXPORT_SYMBOL_GPL(filemap_migrate_folio);
+
 /*
  * Writeback a folio to clean the dirty state
  */