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>

3 files changed, 8 insertions, 16 deletions

diff --git a/fs/lockd/mon.c b/fs/lockd/mon.c
index eb243edf8932..2102e2d0134d 100644
--- a/fs/lockd/mon.c
+++ b/fs/lockd/mon.c
@@ -225,16 +225,13 @@ xdr_decode_stat(struct rpc_rqst *rqstp, __be32 *p, struct nsm_res *resp)
 #define SM_monres_sz    2
 #define SM_unmonres_sz  1
 
-#ifndef MAX
-# define MAX(a, b)      (((a) > (b))? (a) : (b))
-#endif
-
 static struct rpc_procinfo      nsm_procedures[] = {
 [SM_MON] = {
                 .p_proc         = SM_MON,
                 .p_encode       = (kxdrproc_t) xdr_encode_mon,
                 .p_decode       = (kxdrproc_t) xdr_decode_stat_res,
-                .p_bufsiz       = MAX(SM_mon_sz, SM_monres_sz) << 2,
+                .p_arglen       = SM_mon_sz,
+                .p_replen       = SM_monres_sz,
                 .p_statidx      = SM_MON,
                 .p_name         = "MONITOR",
         },
@@ -242,7 +239,8 @@ static struct rpc_procinfo	nsm_procedures[] = {
                 .p_proc         = SM_UNMON,
                 .p_encode       = (kxdrproc_t) xdr_encode_unmon,
                 .p_decode       = (kxdrproc_t) xdr_decode_stat,
-                .p_bufsiz       = MAX(SM_mon_id_sz, SM_unmonres_sz) << 2,
+                .p_arglen       = SM_mon_id_sz,
+                .p_replen       = SM_unmonres_sz,
                 .p_statidx      = SM_UNMON,
                 .p_name         = "UNMONITOR",
         },
diff --git a/fs/lockd/xdr.c b/fs/lockd/xdr.c
index 6aac4b2c9ff0..9702956d206c 100644
--- a/fs/lockd/xdr.c
+++ b/fs/lockd/xdr.c
@@ -534,10 +534,6 @@ nlmclt_decode_res(struct rpc_rqst *req, __be32 *p, struct nlm_res *resp)
 #define NLM_res_sz              NLM_cookie_sz+1
 #define NLM_norep_sz            0
 
-#ifndef MAX
-# define MAX(a, b)              (((a) > (b))? (a) : (b))
-#endif
-
 /*
  * For NLM, a void procedure really returns nothing
  */
@@ -548,7 +544,8 @@ nlmclt_decode_res(struct rpc_rqst *req, __be32 *p, struct nlm_res *resp)
         .p_proc      = NLMPROC_##proc,                                  \
         .p_encode    = (kxdrproc_t) nlmclt_encode_##argtype,            \
         .p_decode    = (kxdrproc_t) nlmclt_decode_##restype,            \
-        .p_bufsiz    = MAX(NLM_##argtype##_sz, NLM_##restype##_sz) << 2,        \
+        .p_arglen    = NLM_##argtype##_sz,                              \
+        .p_replen    = NLM_##restype##_sz,                              \
         .p_statidx   = NLMPROC_##proc,                                  \
         .p_name      = #proc,                                           \
         }
diff --git a/fs/lockd/xdr4.c b/fs/lockd/xdr4.c
index 7c8b679c394c..ce1efdbe1b3a 100644
--- a/fs/lockd/xdr4.c
+++ b/fs/lockd/xdr4.c
@@ -544,10 +544,6 @@ nlm4clt_decode_res(struct rpc_rqst *req, __be32 *p, struct nlm_res *resp)
 #define NLM4_res_sz             NLM4_cookie_sz+1
 #define NLM4_norep_sz           0
 
-#ifndef MAX
-# define MAX(a,b)               (((a) > (b))? (a) : (b))
-#endif
-
 /*
  * For NLM, a void procedure really returns nothing
  */
@@ -558,7 +554,8 @@ nlm4clt_decode_res(struct rpc_rqst *req, __be32 *p, struct nlm_res *resp)
         .p_proc      = NLMPROC_##proc,                                  \
         .p_encode    = (kxdrproc_t) nlm4clt_encode_##argtype,           \
         .p_decode    = (kxdrproc_t) nlm4clt_decode_##restype,           \
-        .p_bufsiz    = MAX(NLM4_##argtype##_sz, NLM4_##restype##_sz) << 2,      \
+        .p_arglen    = NLM4_##argtype##_sz,                             \
+        .p_replen    = NLM4_##restype##_sz,                             \
         .p_statidx   = NLMPROC_##proc,                                  \
         .p_name      = #proc,                                           \
         }