NFSv4.1: Add a module parameter to set the number of session slots

Add the module parameter 'max_session_slots' to set the initial number
of slots that the NFSv4.1 client will attempt to negotiate with the
server.

Signed-off-by: Trond Myklebust <[e-mail]>

Documentation/kernel-parameters.txt

···
 			of returning the full 64-bit number.
 			The default is to return 64-bit inode numbers.
 
+	nfs.max_session_slots=
+			[NFSv4.1] Sets the maximum number of session slots
+			the client will attempt to negotiate with the server.
+			This limits the number of simultaneous RPC requests
+			that the client can send to the NFSv4.1 server.
+			Note that there is little point in setting this
+			value higher than the max_tcp_slot_table_limit.
+
 	nfs.nfs4_disable_idmapping=
 			[NFSv4] When set to the default of '1', this option
 			ensures that both the RPC level authentication

fs/nfs/nfs4proc.c

···
 
 #define NFS4_MAX_LOOP_ON_RECOVER (10)
 
+static unsigned short max_session_slots = NFS4_DEF_SLOT_TABLE_SIZE;
+
 struct nfs4_opendata;
 static int _nfs4_proc_open(struct nfs4_opendata *data);
 static int _nfs4_recover_proc_open(struct nfs4_opendata *data);
···
 	args->fc_attrs.max_rqst_sz = mxrqst_sz;
 	args->fc_attrs.max_resp_sz = mxresp_sz;
 	args->fc_attrs.max_ops = NFS4_MAX_OPS;
-	args->fc_attrs.max_reqs = session->clp->cl_rpcclient->cl_xprt->max_reqs;
+	args->fc_attrs.max_reqs = max_session_slots;
 
 	dprintk("%s: Fore Channel : max_rqst_sz=%u max_resp_sz=%u "
 		"max_ops=%u max_reqs=%u\n",
···
 	&nfs4_xattr_nfs4_acl_handler,
 	NULL
 };
+
+module_param(max_session_slots, ushort, 0644);
+MODULE_PARM_DESC(max_session_slots, "Maximum number of outstanding NFSv4.1 "
+		"requests the client will negotiate");
 
 /*
  * Local variables:

include/linux/nfs_fs_sb.h

···
 
 
 /* maximum number of slots to use */
-#define NFS4_MAX_SLOT_TABLE (128U)
+#define NFS4_DEF_SLOT_TABLE_SIZE (16U)
+#define NFS4_MAX_SLOT_TABLE (256U)
 #define NFS4_NO_SLOT ((u32)-1)
 
 #if defined(CONFIG_NFS_V4)
 
 /* Sessions */
-#define SLOT_TABLE_SZ (NFS4_MAX_SLOT_TABLE/(8*sizeof(long)))
+#define SLOT_TABLE_SZ DIV_ROUND_UP(NFS4_MAX_SLOT_TABLE, 8*sizeof(long))
 struct nfs4_slot_table {
 	struct nfs4_slot *slots;		/* seqid per slot */
 	unsigned long   used_slots[SLOT_TABLE_SZ]; /* used/unused bitmap */