xprtrdma: Allocate req's regbufs at xprt create time

Allocating an rpcrdma_req's regbufs at xprt create time enables
a pair of micro-optimizations:

First, if these regbufs are always there, we can eliminate two
conditional branches from the hot xprt_rdma_allocate path.

Second, by allocating a 1KB buffer, it places a lower bound on the
size of these buffers, without adding yet another conditional
branch. The lower bound reduces the number of hardway re-
allocations. In fact, for some workloads it completely eliminates
hardway allocations.

Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: Anna Schumaker <[email protected]>

net/sunrpc/xprtrdma/backchannel.c

@@ -28,10 +28,10 @@ static int rpcrdma_bc_setup_reqs(struct rpcrdma_xprt *r_xprt,
 	unsigned int i;
 
 	for (i = 0; i < (count << 1); i++) {
-		struct rpcrdma_regbuf *rb;
 		size_t size;
 
-		req = rpcrdma_req_create(r_xprt, GFP_KERNEL);
+		size = min_t(size_t, r_xprt->rx_data.inline_rsize, PAGE_SIZE);
+		req = rpcrdma_req_create(r_xprt, size, GFP_KERNEL);
 		if (!req)
 			return -ENOMEM;
 		rqst = &req->rl_slot;
@@ -42,20 +42,10 @@ static int rpcrdma_bc_setup_reqs(struct rpcrdma_xprt *r_xprt,
 		spin_lock(&xprt->bc_pa_lock);
 		list_add(&rqst->rq_bc_pa_list, &xprt->bc_pa_list);
 		spin_unlock(&xprt->bc_pa_lock);
-
-		size = r_xprt->rx_data.inline_rsize;
-		rb = rpcrdma_alloc_regbuf(size, DMA_TO_DEVICE, GFP_KERNEL);
-		if (!rb)
-			goto out_fail;
-		req->rl_sendbuf = rb;
-		xdr_buf_init(&rqst->rq_snd_buf, rdmab_data(rb),
-			     min_t(size_t, size, PAGE_SIZE));
+		xdr_buf_init(&rqst->rq_snd_buf, rdmab_data(req->rl_sendbuf),
+			     size);
 	}
 	return 0;
-
-out_fail:
-	rpcrdma_req_destroy(req);
-	return -ENOMEM;
 }
 
 /**

net/sunrpc/xprtrdma/transport.c

@@ -591,7 +591,7 @@ rpcrdma_get_sendbuf(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req,
 {
 	struct rpcrdma_regbuf *rb;
 
-	if (req->rl_sendbuf && rdmab_length(req->rl_sendbuf) >= size)
+	if (likely(rdmab_length(req->rl_sendbuf) >= size))
 		return true;
 
 	rb = rpcrdma_alloc_regbuf(size, DMA_TO_DEVICE, flags);
@@ -621,7 +621,7 @@ rpcrdma_get_recvbuf(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req,
 {
 	struct rpcrdma_regbuf *rb;
 
-	if (req->rl_recvbuf && rdmab_length(req->rl_recvbuf) >= size)
+	if (likely(rdmab_length(req->rl_recvbuf) >= size))
 		return true;
 
 	rb = rpcrdma_alloc_regbuf(size, DMA_NONE, flags);

net/sunrpc/xprtrdma/verbs.c

@@ -998,34 +998,51 @@ rpcrdma_mr_refresh_worker(struct work_struct *work)
 /**
  * rpcrdma_req_create - Allocate an rpcrdma_req object
  * @r_xprt: controlling r_xprt
+ * @size: initial size, in bytes, of send and receive buffers
  * @flags: GFP flags passed to memory allocators
  *
  * Returns an allocated and fully initialized rpcrdma_req or NULL.
  */
-struct rpcrdma_req *rpcrdma_req_create(struct rpcrdma_xprt *r_xprt, gfp_t flags)
+struct rpcrdma_req *rpcrdma_req_create(struct rpcrdma_xprt *r_xprt, size_t size,
+				       gfp_t flags)
 {
 	struct rpcrdma_buffer *buffer = &r_xprt->rx_buf;
 	struct rpcrdma_regbuf *rb;
 	struct rpcrdma_req *req;
 
 	req = kzalloc(sizeof(*req), flags);
 	if (req == NULL)
-		return NULL;
+		goto out1;
 
 	rb = rpcrdma_alloc_regbuf(RPCRDMA_HDRBUF_SIZE, DMA_TO_DEVICE, flags);
-	if (!rb) {
-		kfree(req);
-		return NULL;
-	}
+	if (!rb)
+		goto out2;
 	req->rl_rdmabuf = rb;
 	xdr_buf_init(&req->rl_hdrbuf, rdmab_data(rb), rdmab_length(rb));
+
+	req->rl_sendbuf = rpcrdma_alloc_regbuf(size, DMA_TO_DEVICE, flags);
+	if (!req->rl_sendbuf)
+		goto out3;
+
+	req->rl_recvbuf = rpcrdma_alloc_regbuf(size, DMA_NONE, flags);
+	if (!req->rl_recvbuf)
+		goto out4;
+
 	req->rl_buffer = buffer;
 	INIT_LIST_HEAD(&req->rl_registered);
-
 	spin_lock(&buffer->rb_lock);
 	list_add(&req->rl_all, &buffer->rb_allreqs);
 	spin_unlock(&buffer->rb_lock);
 	return req;
+
+out4:
+	kfree(req->rl_sendbuf);
+out3:
+	kfree(req->rl_rdmabuf);
+out2:
+	kfree(req);
+out1:
+	return NULL;
 }
 
 static bool rpcrdma_rep_create(struct rpcrdma_xprt *r_xprt, bool temp)
@@ -1090,7 +1107,8 @@ rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt)
 	for (i = 0; i < buf->rb_max_requests; i++) {
 		struct rpcrdma_req *req;
 
-		req = rpcrdma_req_create(r_xprt, GFP_KERNEL);
+		req = rpcrdma_req_create(r_xprt, RPCRDMA_V1_DEF_INLINE_SIZE,
+					 GFP_KERNEL);
 		if (!req)
 			goto out;
 		list_add(&req->rl_list, &buf->rb_send_bufs);

net/sunrpc/xprtrdma/xprt_rdma.h

@@ -529,7 +529,7 @@ int rpcrdma_ep_post(struct rpcrdma_ia *, struct rpcrdma_ep *,
 /*
  * Buffer calls - xprtrdma/verbs.c
  */
-struct rpcrdma_req *rpcrdma_req_create(struct rpcrdma_xprt *r_xprt,
+struct rpcrdma_req *rpcrdma_req_create(struct rpcrdma_xprt *r_xprt, size_t size,
 				       gfp_t flags);
 void rpcrdma_req_destroy(struct rpcrdma_req *req);
 int rpcrdma_buffer_create(struct rpcrdma_xprt *);