[GFS2] Allow page migration for writeback and ordered pages

To improve performance on NUMA, we use the VM's standard page
migration for writeback and ordered pages. Probably we could
also do the same for journaled data, but that would need a
careful audit of the code, so will be the subject of a later
patch.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/ops_address.c

@@ -1098,6 +1098,7 @@ static const struct address_space_operations gfs2_writeback_aops = {
 	.invalidatepage = gfs2_invalidatepage,
 	.releasepage = gfs2_releasepage,
 	.direct_IO = gfs2_direct_IO,
+	.migratepage = buffer_migrate_page,
 };
 
 static const struct address_space_operations gfs2_ordered_aops = {
@@ -1112,6 +1113,7 @@ static const struct address_space_operations gfs2_ordered_aops = {
 	.invalidatepage = gfs2_invalidatepage,
 	.releasepage = gfs2_releasepage,
 	.direct_IO = gfs2_direct_IO,
+	.migratepage = buffer_migrate_page,
 };
 
 static const struct address_space_operations gfs2_jdata_aops = {