[PATCH] Direct Migration V9: Avoid writeback / page_migrate() method

Migrate a page with buffers without requiring writeback

This introduces a new address space operation migratepage() that may be used
by a filesystem to implement its own version of page migration.

A version is provided that migrates buffers attached to pages.  Some
filesystems (ext2, ext3, xfs) are modified to utilize this feature.

The swapper address space operation are modified so that a regular
migrate_page() will occur for anonymous pages without writeback (migrate_pages
forces every anonymous page to have a swap entry).

Signed-off-by: Mike Kravetz <kravetz@us.ibm.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/xfs/linux-2.6/xfs_aops.c

@@ -1462,4 +1462,5 @@ struct address_space_operations linvfs_aops = {
 	.commit_write		= generic_commit_write,
 	.bmap			= linvfs_bmap,
 	.direct_IO		= linvfs_direct_IO,
+	.migratepage		= buffer_migrate_page,
 };

fs/xfs/linux-2.6/xfs_buf.c

@@ -1521,6 +1521,7 @@ xfs_mapping_buftarg(
 	struct address_space	*mapping;
 	static struct address_space_operations mapping_aops = {
 		.sync_page = block_sync_page,
+		.migratepage = fail_migrate_page,
 	};
 
 	inode = new_inode(bdev->bd_inode->i_sb);