pNFS: Don't allocate more pages than we need to fit a layoutget response

For the 'files' and 'flexfiles' layout types, we do not expect the reply
to be any larger than 4k. The block and scsi layout types are a little more
greedy, so we keep allocating the maximum response size for now.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index ece367e..e2e9fcd 100644
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -125,6 +125,7 @@
 	struct module *owner;
 	unsigned flags;
 	unsigned max_deviceinfo_size;
+	unsigned max_layoutget_response;
 
 	int (*set_layoutdriver) (struct nfs_server *, const struct nfs_fh *);
 	int (*clear_layoutdriver) (struct nfs_server *);