SUNRPC: RPC buffer size estimates are too large

The RPC buffer size estimation logic in net/sunrpc/clnt.c always
significantly overestimates the requirements for the buffer size.
A little instrumentation demonstrated that in fact rpc_malloc was never
allocating the buffer from the mempool, but almost always called kmalloc.

To compute the size of the RPC buffer more precisely, split p_bufsiz into
two fields; one for the argument size, and one for the result size.

Then, compute the sum of the exact call and reply header sizes, and split
the RPC buffer precisely between the two.  That should keep almost all RPC
buffers within the 2KiB buffer mempool limit.

And, we can finally be rid of RPC_SLACK_SPACE!

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 5 insertions, 2 deletions

diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
index c7a78eef2b4f..32c48a0b0d71 100644
--- a/include/linux/sunrpc/clnt.h
+++ b/include/linux/sunrpc/clnt.h
@@ -84,7 +84,8 @@ struct rpc_procinfo {
         u32                     p_proc;         /* RPC procedure number */
         kxdrproc_t              p_encode;       /* XDR encode function */
         kxdrproc_t              p_decode;       /* XDR decode function */
-        unsigned int            p_bufsiz;       /* req. buffer size */
+        unsigned int            p_arglen;       /* argument hdr length (u32) */
+        unsigned int            p_replen;       /* reply hdr length (u32) */
         unsigned int            p_count;        /* call count */
         unsigned int            p_timer;        /* Which RTT timer to use */
         u32                     p_statidx;      /* Which procedure to account */
diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index f780e72fc417..7aa29502b187 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -84,7 +84,9 @@ struct rpc_rqst {
         struct list_head        rq_list;
 
         __u32 *                 rq_buffer;      /* XDR encode buffer */
-        size_t                  rq_bufsize;
+        size_t                  rq_bufsize,
+                                rq_callsize,
+                                rq_rcvsize;
 
         struct xdr_buf          rq_private_buf;         /* The receive buffer
                                                          * used in the softirq.