svcrdma: Introduce svc_rdma_recv_ctxt

svc_rdma_op_ctxt's are pre-allocated and maintained on a per-xprt
free list. This eliminates the overhead of calling kmalloc / kfree,
both of which grab a globally shared lock that disables interrupts.
To reduce contention further, separate the use of these objects in
the Receive and Send paths in svcrdma.

Subsequent patches will take advantage of this separation by
allocating real resources which are then cached in these objects.
The allocations are freed when the transport is torn down.

I've renamed the structure so that static type checking can be used
to ensure that uses of op_ctxt and recv_ctxt are not confused. As an
additional clean up, structure fields are renamed to conform with
kernel coding conventions.

As a final clean up, helpers related to recv_ctxt are moved closer
to the functions that use them.

Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: J. Bruce Fields <[email protected]>

include/linux/sunrpc/svc_rdma.h

@@ -128,6 +128,9 @@ struct svcxprt_rdma {
 	unsigned long	     sc_flags;
 	struct list_head     sc_read_complete_q;
 	struct work_struct   sc_work;
+
+	spinlock_t	     sc_recv_lock;
+	struct list_head     sc_recv_ctxts;
 };
 /* sc_flags */
 #define RDMAXPRT_CONN_PENDING	3
@@ -142,6 +145,19 @@ struct svcxprt_rdma {
 
 #define RPCSVC_MAXPAYLOAD_RDMA	RPCSVC_MAXPAYLOAD
 
+struct svc_rdma_recv_ctxt {
+	struct list_head	rc_list;
+	struct ib_recv_wr	rc_recv_wr;
+	struct ib_cqe		rc_cqe;
+	struct xdr_buf		rc_arg;
+	u32			rc_byte_len;
+	unsigned int		rc_page_count;
+	unsigned int		rc_hdr_count;
+	struct ib_sge		rc_sges[1 +
+					RPCRDMA_MAX_INLINE_THRESH / PAGE_SIZE];
+	struct page		*rc_pages[RPCSVC_MAXPAGES];
+};
+
 /* Track DMA maps for this transport and context */
 static inline void svc_rdma_count_mappings(struct svcxprt_rdma *rdma,
 					   struct svc_rdma_op_ctxt *ctxt)
@@ -155,13 +171,19 @@ extern int svc_rdma_handle_bc_reply(struct rpc_xprt *xprt,
 				    struct xdr_buf *rcvbuf);
 
 /* svc_rdma_recvfrom.c */
+extern void svc_rdma_recv_ctxts_destroy(struct svcxprt_rdma *rdma);
+extern bool svc_rdma_post_recvs(struct svcxprt_rdma *rdma);
+extern void svc_rdma_recv_ctxt_put(struct svcxprt_rdma *rdma,
+				   struct svc_rdma_recv_ctxt *ctxt,
+				   int free_pages);
+extern void svc_rdma_flush_recv_queues(struct svcxprt_rdma *rdma);
 extern int svc_rdma_recvfrom(struct svc_rqst *);
 
 /* svc_rdma_rw.c */
 extern void svc_rdma_destroy_rw_ctxts(struct svcxprt_rdma *rdma);
 extern int svc_rdma_recv_read_chunk(struct svcxprt_rdma *rdma,
 				    struct svc_rqst *rqstp,
-				    struct svc_rdma_op_ctxt *head, __be32 *p);
+				    struct svc_rdma_recv_ctxt *head, __be32 *p);
 extern int svc_rdma_send_write_chunk(struct svcxprt_rdma *rdma,
 				     __be32 *wr_ch, struct xdr_buf *xdr);
 extern int svc_rdma_send_reply_chunk(struct svcxprt_rdma *rdma,