nfs41 do not allocate unused back channel pages

Signed-off-by: Andy Adamson <andros@netapp.com>
[Trond.Myklebust@netapp.com: moved definition of svc_is_backchannel()
 into include/linux/sunrpc/bc_xprt.h.]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/bc_xprt.h

@@ -38,12 +38,27 @@ int xprt_setup_backchannel(struct rpc_xprt *, unsigned int min_reqs);
 void xprt_destroy_backchannel(struct rpc_xprt *, int max_reqs);
 void bc_release_request(struct rpc_task *);
 int bc_send(struct rpc_rqst *req);
+
+/*
+ * Determine if a shared backchannel is in use
+ */
+static inline int svc_is_backchannel(const struct svc_rqst *rqstp)
+{
+	if (rqstp->rq_server->bc_xprt)
+		return 1;
+	return 0;
+}
 #else /* CONFIG_NFS_V4_1 */
 static inline int xprt_setup_backchannel(struct rpc_xprt *xprt,
 					 unsigned int min_reqs)
 {
 	return 0;
 }
+
+static inline int svc_is_backchannel(const struct svc_rqst *rqstp)
+{
+	return 0;
+}
 #endif /* CONFIG_NFS_V4_1 */
 #endif /* _LINUX_SUNRPC_BC_XPRT_H */
 

net/sunrpc/svc.c

@@ -506,6 +506,10 @@ svc_init_buffer(struct svc_rqst *rqstp, unsigned int size)
 {
 	unsigned int pages, arghi;
 
+	/* bc_xprt uses fore channel allocated buffers */
+	if (svc_is_backchannel(rqstp))
+		return 1;
+
 	pages = size / PAGE_SIZE + 1; /* extra page as we hold both request and reply.
 				       * We assume one is at most one page
 				       */