kill spurious reference to vmtruncate

Lots of filesystems calls vmtruncate despite not implementing the old
->truncate method.  Switch them to use simple_setsize and add some
comments about the truncate code where it seems fitting.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index a739a0a..9f8b525 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -700,8 +700,14 @@
 		return 0;
 
 	page_cache_release(page);
+
+	/*
+	 * XXX(hch): the call below should probably be replaced with
+	 * a call to the gfs2-specific truncate blocks helper to actually
+	 * release disk blocks..
+	 */
 	if (pos + len > ip->i_inode.i_size)
-		vmtruncate(&ip->i_inode, ip->i_inode.i_size);
+		simple_setsize(&ip->i_inode, ip->i_inode.i_size);
 out_endtrans:
 	gfs2_trans_end(sdp);
 out_trans_fail: