RDS/IB: create a work queue for FMR flushing

This patch moves the FMR flushing work in to its own mult-threaded work queue.
This is to maintain performance in preparation for returning the main krdsd
work queue back to a single threaded work queue to avoid deep-rooted
concurrency bugs.

This is also good because it further separates FMRs, which might be removed
some day, from the rest of the code base.
Signed-off-by: Zach Brown <zach.brown@oracle.com>

net/rds/ib.c

@@ -351,6 +351,7 @@ void rds_ib_exit(void)
 	rds_ib_sysctl_exit();
 	rds_ib_recv_exit();
 	rds_trans_unregister(&rds_ib_transport);
+	rds_ib_fmr_exit();
 }
 
 struct rds_transport rds_ib_transport = {
@@ -386,10 +387,14 @@ int __init rds_ib_init(void)
 
 	INIT_LIST_HEAD(&rds_ib_devices);
 
-	ret = ib_register_client(&rds_ib_client);
+	ret = rds_ib_fmr_init();
 	if (ret)
 		goto out;
 
+	ret = ib_register_client(&rds_ib_client);
+	if (ret)
+		goto out_fmr_exit;
+
 	ret = rds_ib_sysctl_init();
 	if (ret)
 		goto out_ibreg;
@@ -412,6 +417,8 @@ int __init rds_ib_init(void)
 	rds_ib_sysctl_exit();
 out_ibreg:
 	rds_ib_unregister_client();
+out_fmr_exit:
+	rds_ib_fmr_exit();
 out:
 	return ret;
 }

net/rds/ib.h

@@ -308,6 +308,8 @@ void *rds_ib_get_mr(struct scatterlist *sg, unsigned long nents,
 void rds_ib_sync_mr(void *trans_private, int dir);
 void rds_ib_free_mr(void *trans_private, int invalidate);
 void rds_ib_flush_mrs(void);
+int __init rds_ib_fmr_init(void);
+void __exit rds_ib_fmr_exit(void);
 
 /* ib_recv.c */
 int __init rds_ib_recv_init(void);

net/rds/ib_rdma.c

@@ -691,6 +691,26 @@ static int rds_ib_flush_mr_pool(struct rds_ib_mr_pool *pool,
 	return ret;
 }
 
+struct workqueue_struct *rds_ib_fmr_wq;
+
+int __init rds_ib_fmr_init(void)
+{
+	rds_ib_fmr_wq = create_workqueue("rds_fmr_flushd");
+	if (!rds_ib_fmr_wq)
+		return -ENOMEM;
+	return 0;
+}
+
+/*
+ * By the time this is called all the IB devices should have been torn down and
+ * had their pools freed.  As each pool is freed its work struct is waited on,
+ * so the pool flushing work queue should be idle by the time we get here.
+ */
+void __exit rds_ib_fmr_exit(void)
+{
+	destroy_workqueue(rds_ib_fmr_wq);
+}
+
 static void rds_ib_mr_pool_flush_worker(struct work_struct *work)
 {
 	struct rds_ib_mr_pool *pool = container_of(work, struct rds_ib_mr_pool, flush_worker.work);
@@ -718,7 +738,7 @@ void rds_ib_free_mr(void *trans_private, int invalidate)
 	/* If we've pinned too many pages, request a flush */
 	if (atomic_read(&pool->free_pinned) >= pool->max_free_pinned ||
 	    atomic_read(&pool->dirty_count) >= pool->max_items / 10)
-		queue_delayed_work(rds_wq, &pool->flush_worker, 10);
+		queue_delayed_work(rds_ib_fmr_wq, &pool->flush_worker, 10);
 
 	if (invalidate) {
 		if (likely(!in_interrupt())) {
@@ -726,7 +746,8 @@ void rds_ib_free_mr(void *trans_private, int invalidate)
 		} else {
 			/* We get here if the user created a MR marked
 			 * as use_once and invalidate at the same time. */
-			queue_delayed_work(rds_wq, &pool->flush_worker, 10);
+			queue_delayed_work(rds_ib_fmr_wq,
+					   &pool->flush_worker, 10);
 		}
 	}