NFS: Allow the nfs_pageio_descriptor to signal that a re-coalesce is needed

If an attempt to do pNFS fails, and we have to fall back to writing through
the MDS, then we may want to re-coalesce the requests that we already have
since the block size for the MDS read/writes may be different to that of
the DS read/writes.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/nfs_page.h

@@ -68,7 +68,8 @@ struct nfs_pageio_descriptor {
 	size_t			pg_count;
 	size_t			pg_bsize;
 	unsigned int		pg_base;
-	char			pg_moreio;
+	unsigned char		pg_moreio : 1,
+				pg_recoalesce : 1;
 
 	struct inode		*pg_inode;
 	const struct nfs_pageio_ops *pg_ops;