RDS: flush fmrs before allocating new ones

Flushing FMRs is somewhat expensive, and is currently kicked off when
the interrupt handler notices that we are getting low.  The result of
this is that FMR flushing only happens from the interrupt cpus.

This spreads the load more effectively by triggering flushes just before
we allocate a new FMR.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

net/rds/ib_rdma.c

@@ -38,6 +38,8 @@
 #include "ib.h"
 #include "xlist.h"
 
+struct workqueue_struct *rds_ib_fmr_wq;
+
 static DEFINE_PER_CPU(unsigned long, clean_list_grace);
 #define CLEAN_LIST_BUSY_BIT 0
 
@@ -304,6 +306,9 @@ static struct rds_ib_mr *rds_ib_alloc_fmr(struct rds_ib_device *rds_ibdev)
 	struct rds_ib_mr *ibmr = NULL;
 	int err = 0, iter = 0;
 
+	if (atomic_read(&pool->dirty_count) >= pool->max_items / 10)
+		queue_delayed_work(rds_ib_fmr_wq, &pool->flush_worker, 10);
+
 	while (1) {
 		ibmr = rds_ib_reuse_fmr(pool);
 		if (ibmr)
@@ -691,8 +696,6 @@ static int rds_ib_flush_mr_pool(struct rds_ib_mr_pool *pool,
 	return ret;
 }
 
-struct workqueue_struct *rds_ib_fmr_wq;
-
 int rds_ib_fmr_init(void)
 {
 	rds_ib_fmr_wq = create_workqueue("rds_fmr_flushd");