SUNRPC: Optimise away unnecessary data moves in xdr_align_pages

We only have to call xdr_shrink_pagelen() if the remaining RPC
message does not fit in the page buffer length that we supplied
to xdr_align_pages().
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/xdr.c

@@ -730,21 +730,24 @@ static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
 
 	if (xdr->nwords == 0)
 		return 0;
-	if (nwords > xdr->nwords) {
-		nwords = xdr->nwords;
-		len = nwords << 2;
-	}
 	/* Realign pages to current pointer position */
 	iov  = buf->head;
-	if (iov->iov_len > cur)
+	if (iov->iov_len > cur) {
 		xdr_shrink_bufhead(buf, iov->iov_len - cur);
+		xdr->nwords = XDR_QUADLEN(buf->len - cur);
+	}
 
-	/* Truncate page data and move it into the tail */
-	if (buf->page_len > len)
-		xdr_shrink_pagelen(buf, buf->page_len - len);
-	else
+	if (nwords > xdr->nwords) {
+		nwords = xdr->nwords;
+		len = nwords << 2;
+	}
+	if (buf->page_len <= len)
 		len = buf->page_len;
-	xdr->nwords = XDR_QUADLEN(buf->len - cur);
+	else if (nwords < xdr->nwords) {
+		/* Truncate page data and move it into the tail */
+		xdr_shrink_pagelen(buf, buf->page_len - len);
+		xdr->nwords = XDR_QUADLEN(buf->len - cur);
+	}
 	return len;
 }