For xprtrdma, the RPC Call and Reply buffers are involved in real
I/O operations.

To start with, the DMA direction of the I/O for a Call is opposite
that of a Reply.

In the current arrangement, the Reply buffer address is on a
four-byte alignment just past the call buffer. Would be friendlier
on some platforms if that was at a DMA cache alignment instead.

Because the current arrangement allocates a single memory region
which contains both buffers, the RPC Reply buffer often contains a
page boundary in it when the Call buffer is large enough (which is
frequent).

It would be a little nicer for setting up DMA operations (and
possible registration of the Reply buffer) if the two buffers were
separated, well-aligned, and contained as few page boundaries as
possible.

Now, I could just pad out the single memory region used for the pair
of buffers. But frequently that would mean a lot of unused space to
ensure the Reply buffer did not have a page boundary.

Add a separate pointer to rpc_rqst that points right to the RPC
Reply buffer. This makes no difference to xprtsock, but it will help
xprtrdma in subsequent patches.

Signed-off-by: Chuck Lever <redacted>
---
 include/linux/sunrpc/xprt.h     |    5 +++--
 net/sunrpc/clnt.c               |    2 +-
 net/sunrpc/sched.c              |    1 +
 net/sunrpc/xprtrdma/transport.c |    1 +
 4 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 72c2aeb..46f069e 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h

@@ -84,8 +84,9 @@ struct rpc_rqst {
 	struct list_head	rq_list;
 
 	void			*rq_buffer;	/* Call XDR encode buffer */
-	size_t			rq_callsize,
-				rq_rcvsize;
+	size_t			rq_callsize;
+	void			*rq_rbuffer;	/* Reply XDR decode buffer */
+	size_t			rq_rcvsize;

 	size_t			rq_xmit_bytes_sent;	/* total bytes sent */
 	size_t			rq_reply_bytes_recvd;	/* total reply bytes */
 							/* received */

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index ab467c0..fd389c0 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c

@@ -1768,7 +1768,7 @@ rpc_xdr_encode(struct rpc_task *task)
 		     req->rq_buffer,
 		     req->rq_callsize);
 	xdr_buf_init(&req->rq_rcv_buf,
-		     (char *)req->rq_buffer + req->rq_callsize,
+		     req->rq_rbuffer,
 		     req->rq_rcvsize);
 
 	p = rpc_encode_header(task);

diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 6690ebc..5db68b3 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c

@@ -891,6 +891,7 @@ int rpc_malloc(struct rpc_task *task)
 	dprintk("RPC: %5u allocated buffer of size %zu at %p\n",
 			task->tk_pid, size, buf);
 	rqst->rq_buffer = buf->data;
+	rqst->rq_rbuffer = (char *)rqst->rq_buffer + rqst->rq_callsize;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(rpc_malloc);

diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index ebf14ba..136caf3 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c

@@ -524,6 +524,7 @@ out:
 	dprintk("RPC:       %s: size %zd, request 0x%p\n", __func__, size, req);
 	req->rl_connect_cookie = 0;	/* our reserved value */
 	rqst->rq_buffer = req->rl_sendbuf->rg_base;
+	rqst->rq_rbuffer = (char *)rqst->rq_buffer + rqst->rq_rcvsize;
 	return 0;
 
 out_rdmabuf:

--

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