SUNRPC: Support dynamic slot allocation for TCP connections

Allow the number of available slots to grow with the TCP window size.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 59 insertions, 11 deletions

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index ea7b3c16cddd..be85cf04a479 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -935,25 +935,66 @@ void xprt_transmit(struct rpc_task *task)
         spin_unlock_bh(&xprt->transport_lock);
 }
 
+static struct rpc_rqst *xprt_dynamic_alloc_slot(struct rpc_xprt *xprt, gfp_t gfp_flags)
+{
+        struct rpc_rqst *req = ERR_PTR(-EAGAIN);
+
+        if (!atomic_add_unless(&xprt->num_reqs, 1, xprt->max_reqs))
+                goto out;
+        req = kzalloc(sizeof(struct rpc_rqst), gfp_flags);
+        if (req != NULL)
+                goto out;
+        atomic_dec(&xprt->num_reqs);
+        req = ERR_PTR(-ENOMEM);
+out:
+        return req;
+}
+
+static bool xprt_dynamic_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
+{
+        if (atomic_add_unless(&xprt->num_reqs, -1, xprt->min_reqs)) {
+                kfree(req);
+                return true;
+        }
+        return false;
+}
+
 static void xprt_alloc_slot(struct rpc_task *task)
 {
         struct rpc_xprt *xprt = task->tk_xprt;
+        struct rpc_rqst *req;
 
-        task->tk_status = 0;
         if (!list_empty(&xprt->free)) {
-                struct rpc_rqst *req = list_entry(xprt->free.next, struct rpc_rqst, rq_list);
-                list_del_init(&req->rq_list);
-                task->tk_rqstp = req;
-                xprt_request_init(task, xprt);
-                return;
+                req = list_entry(xprt->free.next, struct rpc_rqst, rq_list);
+                list_del(&req->rq_list);
+                goto out_init_req;
+        }
+        req = xprt_dynamic_alloc_slot(xprt, GFP_NOWAIT);
+        if (!IS_ERR(req))
+                goto out_init_req;
+        switch (PTR_ERR(req)) {
+        case -ENOMEM:
+                rpc_delay(task, HZ >> 2);
+                dprintk("RPC:       dynamic allocation of request slot "
+                                "failed! Retrying\n");
+                break;
+        case -EAGAIN:
+                rpc_sleep_on(&xprt->backlog, task, NULL);
+                dprintk("RPC:       waiting for request slot\n");
         }
-        dprintk("RPC:       waiting for request slot\n");
         task->tk_status = -EAGAIN;
-        rpc_sleep_on(&xprt->backlog, task, NULL);
+        return;
+out_init_req:
+        task->tk_status = 0;
+        task->tk_rqstp = req;
+        xprt_request_init(task, xprt);
 }
 
 static void xprt_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
 {
+        if (xprt_dynamic_free_slot(xprt, req))
+                return;
+
         memset(req, 0, sizeof(*req));   /* mark unused */
 
         spin_lock(&xprt->reserve_lock);
@@ -972,7 +1013,9 @@ static void xprt_free_all_slots(struct rpc_xprt *xprt)
         }
 }
 
-struct rpc_xprt *xprt_alloc(struct net *net, int size, int num_prealloc)
+struct rpc_xprt *xprt_alloc(struct net *net, size_t size,
+                unsigned int num_prealloc,
+                unsigned int max_alloc)
 {
         struct rpc_xprt *xprt;
         struct rpc_rqst *req;
@@ -992,7 +1035,12 @@ struct rpc_xprt *xprt_alloc(struct net *net, int size, int num_prealloc)
         }
         if (i < num_prealloc)
                 goto out_free;
-        xprt->max_reqs = num_prealloc;
+        if (max_alloc > num_prealloc)
+                xprt->max_reqs = max_alloc;
+        else
+                xprt->max_reqs = num_prealloc;
+        xprt->min_reqs = num_prealloc;
+        atomic_set(&xprt->num_reqs, num_prealloc);
 
         return xprt;
 
@@ -1036,7 +1084,6 @@ void xprt_reserve(struct rpc_task *task)
         if (!xprt_lock_write(xprt, task))
                 return;
 
-        task->tk_status = -EIO;
         spin_lock(&xprt->reserve_lock);
         xprt_alloc_slot(task);
         spin_unlock(&xprt->reserve_lock);
@@ -1057,6 +1104,7 @@ static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
 {
         struct rpc_rqst *req = task->tk_rqstp;
 
+        INIT_LIST_HEAD(&req->rq_list);
         req->rq_timeout = task->tk_client->cl_timeout->to_initval;
         req->rq_task    = task;
         req->rq_xprt    = xprt;