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>

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",
 	},

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,						\
 	}

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,						\
 	}

fs/nfs/mount_clnt.c

@@ -133,13 +133,15 @@ xdr_decode_fhstatus3(struct rpc_rqst *req, __be32 *p, struct mnt_fhstatus *res)
 
 #define MNT_dirpath_sz		(1 + 256)
 #define MNT_fhstatus_sz		(1 + 8)
+#define MNT_fhstatus3_sz	(1 + 16)
 
 static struct rpc_procinfo	mnt_procedures[] = {
 [MNTPROC_MNT] = {
 	  .p_proc		= MNTPROC_MNT,
 	  .p_encode		= (kxdrproc_t) xdr_encode_dirpath,	
 	  .p_decode		= (kxdrproc_t) xdr_decode_fhstatus,
-	  .p_bufsiz		= MNT_dirpath_sz << 2,
+	  .p_arglen		= MNT_dirpath_sz,
+	  .p_replen		= MNT_fhstatus_sz,
 	  .p_statidx		= MNTPROC_MNT,
 	  .p_name		= "MOUNT",
 	},
@@ -150,7 +152,8 @@ static struct rpc_procinfo mnt3_procedures[] = {
 	  .p_proc		= MOUNTPROC3_MNT,
 	  .p_encode		= (kxdrproc_t) xdr_encode_dirpath,
 	  .p_decode		= (kxdrproc_t) xdr_decode_fhstatus3,
-	  .p_bufsiz		= MNT_dirpath_sz << 2,
+	  .p_arglen		= MNT_dirpath_sz,
+	  .p_replen		= MNT_fhstatus3_sz,
 	  .p_statidx		= MOUNTPROC3_MNT,
 	  .p_name		= "MOUNT",
 	},

fs/nfs/nfs2xdr.c

@@ -687,16 +687,13 @@ nfs_stat_to_errno(int stat)
 	return nfs_errtbl[i].errno;
 }
 
-#ifndef MAX
-# define MAX(a, b)	(((a) > (b))? (a) : (b))
-#endif
-
 #define PROC(proc, argtype, restype, timer)				\
 [NFSPROC_##proc] = {							\
 	.p_proc	    =  NFSPROC_##proc,					\
 	.p_encode   =  (kxdrproc_t) nfs_xdr_##argtype,			\
 	.p_decode   =  (kxdrproc_t) nfs_xdr_##restype,			\
-	.p_bufsiz   =  MAX(NFS_##argtype##_sz,NFS_##restype##_sz) << 2,	\
+	.p_arglen   =  NFS_##argtype##_sz,				\
+	.p_replen   =  NFS_##restype##_sz,				\
 	.p_timer    =  timer,						\
 	.p_statidx  =  NFSPROC_##proc,					\
 	.p_name     =  #proc,						\

fs/nfs/nfs3xdr.c

@@ -1102,16 +1102,13 @@ nfs3_xdr_setaclres(struct rpc_rqst *req, __be32 *p, struct nfs_fattr *fattr)
 }
 #endif  /* CONFIG_NFS_V3_ACL */
 
-#ifndef MAX
-# define MAX(a, b)	(((a) > (b))? (a) : (b))
-#endif
-
 #define PROC(proc, argtype, restype, timer)				\
 [NFS3PROC_##proc] = {							\
 	.p_proc      = NFS3PROC_##proc,					\
 	.p_encode    = (kxdrproc_t) nfs3_xdr_##argtype,			\
 	.p_decode    = (kxdrproc_t) nfs3_xdr_##restype,			\
-	.p_bufsiz    = MAX(NFS3_##argtype##_sz,NFS3_##restype##_sz) << 2,	\
+	.p_arglen    = NFS3_##argtype##_sz,				\
+	.p_replen    = NFS3_##restype##_sz,				\
 	.p_timer     = timer,						\
 	.p_statidx   = NFS3PROC_##proc,					\
 	.p_name      = #proc,						\
@@ -1153,7 +1150,8 @@ static struct rpc_procinfo	nfs3_acl_procedures[] = {
 		.p_proc = ACLPROC3_GETACL,
 		.p_encode = (kxdrproc_t) nfs3_xdr_getaclargs,
 		.p_decode = (kxdrproc_t) nfs3_xdr_getaclres,
-		.p_bufsiz = MAX(ACL3_getaclargs_sz, ACL3_getaclres_sz) << 2,
+		.p_arglen = ACL3_getaclargs_sz,
+		.p_replen = ACL3_getaclres_sz,
 		.p_timer = 1,
 		.p_name = "GETACL",
 	},
@@ -1161,7 +1159,8 @@ static struct rpc_procinfo	nfs3_acl_procedures[] = {
 		.p_proc = ACLPROC3_SETACL,
 		.p_encode = (kxdrproc_t) nfs3_xdr_setaclargs,
 		.p_decode = (kxdrproc_t) nfs3_xdr_setaclres,
-		.p_bufsiz = MAX(ACL3_setaclargs_sz, ACL3_setaclres_sz) << 2,
+		.p_arglen = ACL3_setaclargs_sz,
+		.p_replen = ACL3_setaclres_sz,
 		.p_timer = 0,
 		.p_name = "SETACL",
 	},

fs/nfs/nfs4xdr.c

@@ -4546,16 +4546,13 @@ nfs4_stat_to_errno(int stat)
 	return stat;
 }
 
-#ifndef MAX
-# define MAX(a, b)	(((a) > (b))? (a) : (b))
-#endif
-
 #define PROC(proc, argtype, restype)				\
 [NFSPROC4_CLNT_##proc] = {					\
 	.p_proc   = NFSPROC4_COMPOUND,				\
 	.p_encode = (kxdrproc_t) nfs4_xdr_##argtype,		\
 	.p_decode = (kxdrproc_t) nfs4_xdr_##restype,		\
-	.p_bufsiz = MAX(NFS4_##argtype##_sz,NFS4_##restype##_sz) << 2,	\
+	.p_arglen = NFS4_##argtype##_sz,			\
+	.p_replen = NFS4_##restype##_sz,			\
 	.p_statidx = NFSPROC4_CLNT_##proc,			\
 	.p_name   = #proc,					\
     }

fs/nfsd/nfs4callback.c

@@ -315,16 +315,13 @@ nfs4_xdr_dec_cb_recall(struct rpc_rqst *rqstp, __be32 *p)
 /*
  * RPC procedure tables
  */
-#ifndef MAX
-# define MAX(a, b)      (((a) > (b))? (a) : (b))
-#endif
-
 #define PROC(proc, call, argtype, restype)                              \
 [NFSPROC4_CLNT_##proc] = {                                      	\
         .p_proc   = NFSPROC4_CB_##call,					\
         .p_encode = (kxdrproc_t) nfs4_xdr_##argtype,                    \
         .p_decode = (kxdrproc_t) nfs4_xdr_##restype,                    \
-        .p_bufsiz = MAX(NFS4_##argtype##_sz,NFS4_##restype##_sz) << 2,  \
+        .p_arglen = NFS4_##argtype##_sz,                                \
+        .p_replen = NFS4_##restype##_sz,                                \
         .p_statidx = NFSPROC4_CB_##call,				\
 	.p_name   = #proc,                                              \
 }

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 */

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.

net/sunrpc/clnt.c

@@ -36,8 +36,6 @@
 #include <linux/sunrpc/metrics.h>
 
 
-#define RPC_SLACK_SPACE		(1024)	/* total overkill */
-
 #ifdef RPC_DEBUG
 # define RPCDBG_FACILITY	RPCDBG_CALL
 #endif
@@ -747,21 +745,37 @@ call_reserveresult(struct rpc_task *task)
 static void
 call_allocate(struct rpc_task *task)
 {
+	unsigned int slack = task->tk_auth->au_cslack;
 	struct rpc_rqst *req = task->tk_rqstp;
 	struct rpc_xprt *xprt = task->tk_xprt;
-	unsigned int	bufsiz;
+	struct rpc_procinfo *proc = task->tk_msg.rpc_proc;
 
 	dprint_status(task);
 
+	task->tk_status = 0;
 	task->tk_action = call_bind;
+
 	if (req->rq_buffer)
 		return;
 
-	/* FIXME: compute buffer requirements more exactly using
-	 * auth->au_wslack */
-	bufsiz = task->tk_msg.rpc_proc->p_bufsiz + RPC_SLACK_SPACE;
+	if (proc->p_proc != 0) {
+		BUG_ON(proc->p_arglen == 0);
+		if (proc->p_decode != NULL)
+			BUG_ON(proc->p_replen == 0);
+	}
 
-	if (xprt->ops->buf_alloc(task, bufsiz << 1) != NULL)
+	/*
+	 * Calculate the size (in quads) of the RPC call
+	 * and reply headers, and convert both values
+	 * to byte sizes.
+	 */
+	req->rq_callsize = RPC_CALLHDRSIZE + (slack << 1) + proc->p_arglen;
+	req->rq_callsize <<= 2;
+	req->rq_rcvsize = RPC_REPHDRSIZE + slack + proc->p_replen;
+	req->rq_rcvsize <<= 2;
+
+	xprt->ops->buf_alloc(task, req->rq_callsize + req->rq_rcvsize);
+	if (req->rq_buffer != NULL)
 		return;
 
 	dprintk("RPC: %5u rpc_buffer allocation failed\n", task->tk_pid);
@@ -788,6 +802,17 @@ rpc_task_force_reencode(struct rpc_task *task)
 	task->tk_rqstp->rq_snd_buf.len = 0;
 }
 
+static inline void
+rpc_xdr_buf_init(struct xdr_buf *buf, void *start, size_t len)
+{
+	buf->head[0].iov_base = start;
+	buf->head[0].iov_len = len;
+	buf->tail[0].iov_len = 0;
+	buf->page_len = 0;
+	buf->len = 0;
+	buf->buflen = len;
+}
+
 /*
  * 3.	Encode arguments of an RPC call
  */
@@ -795,28 +820,17 @@ static void
 call_encode(struct rpc_task *task)
 {
 	struct rpc_rqst	*req = task->tk_rqstp;
-	struct xdr_buf *sndbuf = &req->rq_snd_buf;
-	struct xdr_buf *rcvbuf = &req->rq_rcv_buf;
-	unsigned int	bufsiz;
 	kxdrproc_t	encode;
 	__be32		*p;
 
 	dprint_status(task);
 
-	/* Default buffer setup */
-	bufsiz = req->rq_bufsize >> 1;
-	sndbuf->head[0].iov_base = (void *)req->rq_buffer;
-	sndbuf->head[0].iov_len  = bufsiz;
-	sndbuf->tail[0].iov_len  = 0;
-	sndbuf->page_len	 = 0;
-	sndbuf->len		 = 0;
-	sndbuf->buflen		 = bufsiz;
-	rcvbuf->head[0].iov_base = (void *)((char *)req->rq_buffer + bufsiz);
-	rcvbuf->head[0].iov_len  = bufsiz;
-	rcvbuf->tail[0].iov_len  = 0;
-	rcvbuf->page_len	 = 0;
-	rcvbuf->len		 = 0;
-	rcvbuf->buflen		 = bufsiz;
+	rpc_xdr_buf_init(&req->rq_snd_buf,
+			 req->rq_buffer,
+			 req->rq_callsize);
+	rpc_xdr_buf_init(&req->rq_rcv_buf,
+			 (char *)req->rq_buffer + req->rq_callsize,
+			 req->rq_rcvsize);
 
 	/* Encode header and provided arguments */
 	encode = task->tk_msg.rpc_proc->p_encode;

net/sunrpc/pmap_clnt.c

@@ -335,7 +335,8 @@ static struct rpc_procinfo	pmap_procedures[] = {
 	  .p_proc		= PMAP_SET,
 	  .p_encode		= (kxdrproc_t) xdr_encode_mapping,
 	  .p_decode		= (kxdrproc_t) xdr_decode_bool,
-	  .p_bufsiz		= 4,
+	  .p_arglen		= 4,
+	  .p_replen		= 1,
 	  .p_count		= 1,
 	  .p_statidx		= PMAP_SET,
 	  .p_name		= "SET",
@@ -344,7 +345,8 @@ static struct rpc_procinfo	pmap_procedures[] = {
 	  .p_proc		= PMAP_UNSET,
 	  .p_encode		= (kxdrproc_t) xdr_encode_mapping,
 	  .p_decode		= (kxdrproc_t) xdr_decode_bool,
-	  .p_bufsiz		= 4,
+	  .p_arglen		= 4,
+	  .p_replen		= 1,
 	  .p_count		= 1,
 	  .p_statidx		= PMAP_UNSET,
 	  .p_name		= "UNSET",
@@ -353,7 +355,8 @@ static struct rpc_procinfo	pmap_procedures[] = {
 	  .p_proc		= PMAP_GETPORT,
 	  .p_encode		= (kxdrproc_t) xdr_encode_mapping,
 	  .p_decode		= (kxdrproc_t) xdr_decode_port,
-	  .p_bufsiz		= 4,
+	  .p_arglen		= 4,
+	  .p_replen		= 1,
 	  .p_count		= 1,
 	  .p_statidx		= PMAP_GETPORT,
 	  .p_name		= "GETPORT",

net/sunrpc/xprt.c

@@ -823,7 +823,6 @@ static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
 	req->rq_task	= task;
 	req->rq_xprt    = xprt;
 	req->rq_buffer  = NULL;
-	req->rq_bufsize = 0;
 	req->rq_xid     = xprt_alloc_xid(xprt);
 	req->rq_release_snd_buf = NULL;
 	xprt_reset_majortimeo(req);