dm-buffered: clean up workqueues

Documentation/core-api/workqueue.rst says that create_*workqueue()
functions are deprecated. This patch changes them to alloc_workqueue.

buffered_flush_ws is unused, this patch deletes it.

For bc->buffered_wq, we allow 16 concurrent workqueue threads per CPU,
hopefully this is enough to provide some level of concurrency and it won't
stall the whole system with too many workqueues.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-buffered-target.c |   16 ++--------------
 1 file changed, 2 insertions(+), 14 deletions(-)

Index: linux-2.6/drivers/md/dm-buffered-target.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-buffered-target.c
+++ linux-2.6/drivers/md/dm-buffered-target.c
@@ -29,7 +29,6 @@ enum {	S_BUFFER_SPLITS, S_PREFLUSHS, S_F
 struct buffered_c {
 	struct dm_bufio_client *bufio;
 	struct workqueue_struct *buffered_wq;
-	struct workqueue_struct *buffered_flush_wq;
 	struct delayed_work buffered_flush_ws;
 	mempool_t async_request_pool;
 	struct workqueue_struct *buffered_async_wq;
@@ -539,8 +538,6 @@ static void buffered_dtr(struct dm_targe
 
 	if (bc->buffered_wq)
 		destroy_workqueue(bc->buffered_wq);
-	if (bc->buffered_flush_wq)
-		destroy_workqueue(bc->buffered_flush_wq);
 	if (bc->buffered_async_wq)
 		destroy_workqueue(bc->buffered_async_wq);
 	mempool_exit(&bc->async_request_pool);
@@ -634,23 +631,15 @@ static int buffered_ctr(struct dm_target
 		goto bad;
 	}
 
-	bc->buffered_wq = create_workqueue("dm-" DM_MSG_PREFIX "-io");
+	bc->buffered_wq = alloc_workqueue("dm-" DM_MSG_PREFIX "-io", WQ_MEM_RECLAIM, 16);
 	if (!bc->buffered_wq) {
 		ti->error = "Couldn't start dm-" DM_MSG_PREFIX "-io";
 		r = -ENOMEM;
 		goto bad;
 	}
 
-	bc->buffered_flush_wq = create_singlethread_workqueue("dm-" DM_MSG_PREFIX "-flush");
-	if (!bc->buffered_flush_wq) {
-		ti->error = "Couldn't start dm-" DM_MSG_PREFIX "-flush";
-		r = -ENOMEM;
-		goto bad;
-	}
-
 	if (bc->async_memcpy) {
-		/* FIXME: multithread workqueue? */
-		bc->buffered_async_wq = create_singlethread_workqueue("dm-" DM_MSG_PREFIX "-async");
+		bc->buffered_async_wq = alloc_workqueue("dm-" DM_MSG_PREFIX "-async", WQ_MEM_RECLAIM, 1);
 		if (!bc->buffered_async_wq) {
 			ti->error = "Couldn't start dm-" DM_MSG_PREFIX "-async";
 			r = -ENOMEM;
@@ -726,7 +715,6 @@ static void buffered_postsuspend(struct
 
 	flush_workqueue(bc->buffered_wq);
 	cancel_delayed_work_sync(&bc->buffered_flush_ws);
-	flush_workqueue(bc->buffered_flush_wq);
 	dm_bufio_write_dirty_buffers(bc->bufio);
 }