rxrpc: Preallocate peers, conns and calls for incoming service requests

Make it possible for the data_ready handler called from the UDP transport
socket to completely instantiate an rxrpc_call structure and make it
immediately live by preallocating all the memory it might need.  The idea
is to cut out the background thread usage as much as possible.

[Note that the preallocated structs are not actually used in this patch -
 that will be done in a future patch.]

If insufficient resources are available in the preallocation buffers, it
will be possible to discard the DATA packet in the data_ready handler or
schedule a BUSY packet without the need to schedule an attempt at
allocation in a background thread.

To this end:

 (1) Preallocate rxrpc_peer, rxrpc_connection and rxrpc_call structs to a
     maximum number each of the listen backlog size.  The backlog size is
     limited to a maxmimum of 32.  Only this many of each can be in the
     preallocation buffer.

 (2) For userspace sockets, the preallocation is charged initially by
     listen() and will be recharged by accepting or rejecting pending
     new incoming calls.

 (3) For kernel services {,re,dis}charging of the preallocation buffers is
     handled manually.  Two notifier callbacks have to be provided before
     kernel_listen() is invoked:

     (a) An indication that a new call has been instantiated.  This can be
     	 used to trigger background recharging.

     (b) An indication that a call is being discarded.  This is used when
     	 the socket is being released.

     A function, rxrpc_kernel_charge_accept() is called by the kernel
     service to preallocate a single call.  It should be passed the user ID
     to be used for that call and a callback to associate the rxrpc call
     with the kernel service's side of the ID.

 (4) Discard the preallocation when the socket is closed.

 (5) Temporarily bump the refcount on the call allocated in
     rxrpc_incoming_call() so that rxrpc_release_call() can ditch the
     preallocation ref on service calls unconditionally.  This will no
     longer be necessary once the preallocation is used.

Note that this does not yet control the number of active service calls on a
client - that will come in a later patch.

A future development would be to provide a setsockopt() call that allows a
userspace server to manually charge the preallocation buffer.  This would
allow user call IDs to be provided in advance and the awkward manual accept
stage to be bypassed.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 68 insertions, 3 deletions

diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index 53750de..720ef05 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -18,6 +18,7 @@
 
 struct socket *afs_socket; /* my RxRPC socket */
 static struct workqueue_struct *afs_async_calls;
+static struct afs_call *afs_spare_incoming_call;
 static atomic_t afs_outstanding_calls;
 
 static void afs_free_call(struct afs_call *);
@@ -26,7 +27,8 @@ static int afs_wait_for_call_to_complete(struct afs_call *);
 static void afs_wake_up_async_call(struct sock *, struct rxrpc_call *, unsigned long);
 static int afs_dont_wait_for_call_to_complete(struct afs_call *);
 static void afs_process_async_call(struct work_struct *);
-static void afs_rx_new_call(struct sock *);
+static void afs_rx_new_call(struct sock *, struct rxrpc_call *, unsigned long);
+static void afs_rx_discard_new_call(struct rxrpc_call *, unsigned long);
 static int afs_deliver_cm_op_id(struct afs_call *);
 
 /* synchronous call management */
@@ -54,8 +56,10 @@ static const struct afs_call_type afs_RXCMxxxx = {
 };
 
 static void afs_collect_incoming_call(struct work_struct *);
+static void afs_charge_preallocation(struct work_struct *);
 
 static DECLARE_WORK(afs_collect_incoming_call_work, afs_collect_incoming_call);
+static DECLARE_WORK(afs_charge_preallocation_work, afs_charge_preallocation);
 
 static int afs_wait_atomic_t(atomic_t *p)
 {
@@ -100,13 +104,15 @@ int afs_open_socket(void)
 	if (ret < 0)
 		goto error_2;
 
-	rxrpc_kernel_new_call_notification(socket, afs_rx_new_call);
+	rxrpc_kernel_new_call_notification(socket, afs_rx_new_call,
+					   afs_rx_discard_new_call);
 
 	ret = kernel_listen(socket, INT_MAX);
 	if (ret < 0)
 		goto error_2;
 
 	afs_socket = socket;
+	afs_charge_preallocation(NULL);
 	_leave(" = 0");
 	return 0;
 
@@ -126,6 +132,12 @@ void afs_close_socket(void)
 {
 	_enter("");
 
+	if (afs_spare_incoming_call) {
+		atomic_inc(&afs_outstanding_calls);
+		afs_free_call(afs_spare_incoming_call);
+		afs_spare_incoming_call = NULL;
+	}
+
 	_debug("outstanding %u", atomic_read(&afs_outstanding_calls));
 	wait_on_atomic_t(&afs_outstanding_calls, afs_wait_atomic_t,
 			 TASK_UNINTERRUPTIBLE);
@@ -635,12 +647,65 @@ static void afs_collect_incoming_call(struct work_struct *work)
 		afs_free_call(call);
 }
 
+static void afs_rx_attach(struct rxrpc_call *rxcall, unsigned long user_call_ID)
+{
+	struct afs_call *call = (struct afs_call *)user_call_ID;
+
+	call->rxcall = rxcall;
+}
+
+/*
+ * Charge the incoming call preallocation.
+ */
+static void afs_charge_preallocation(struct work_struct *work)
+{
+	struct afs_call *call = afs_spare_incoming_call;
+
+	for (;;) {
+		if (!call) {
+			call = kzalloc(sizeof(struct afs_call), GFP_KERNEL);
+			if (!call)
+				break;
+
+			INIT_WORK(&call->async_work, afs_process_async_call);
+			call->wait_mode = &afs_async_incoming_call;
+			call->type = &afs_RXCMxxxx;
+			init_waitqueue_head(&call->waitq);
+			call->state = AFS_CALL_AWAIT_OP_ID;
+		}
+
+		if (rxrpc_kernel_charge_accept(afs_socket,
+					       afs_wake_up_async_call,
+					       afs_rx_attach,
+					       (unsigned long)call,
+					       GFP_KERNEL) < 0)
+			break;
+		call = NULL;
+	}
+	afs_spare_incoming_call = call;
+}
+
+/*
+ * Discard a preallocated call when a socket is shut down.
+ */
+static void afs_rx_discard_new_call(struct rxrpc_call *rxcall,
+				    unsigned long user_call_ID)
+{
+	struct afs_call *call = (struct afs_call *)user_call_ID;
+
+	atomic_inc(&afs_outstanding_calls);
+	call->rxcall = NULL;
+	afs_free_call(call);
+}
+
 /*
  * Notification of an incoming call.
  */
-static void afs_rx_new_call(struct sock *sk)
+static void afs_rx_new_call(struct sock *sk, struct rxrpc_call *rxcall,
+			    unsigned long user_call_ID)
 {
 	queue_work(afs_wq, &afs_collect_incoming_call_work);
+	queue_work(afs_wq, &afs_charge_preallocation_work);
 }
 
 /*