ceph: fsc->*_wq's aren't used in memory reclaim path

fsc->*_wq's aren't depended upon during memory reclaim. Convert to
alloc_workqueue() w/o WQ_MEM_RECLAIM.

Signed-off-by: Tejun Heo <[e-mail]>
Cc: Sage Weil <[e-mail]>
Cc: [e-mail]
Signed-off-by: Sage Weil <[e-mail]>

fs/ceph/super.c

···
 		goto fail_client;
 
 	err = -ENOMEM;
-	fsc->wb_wq = create_workqueue("ceph-writeback");
+	/*
+	 * The number of concurrent works can be high but they don't need
+	 * to be processed in parallel, limit concurrency.
+	 */
+	fsc->wb_wq = alloc_workqueue("ceph-writeback", 0, 1);
 	if (fsc->wb_wq == NULL)
 		goto fail_bdi;
-	fsc->pg_inv_wq = create_singlethread_workqueue("ceph-pg-invalid");
+	fsc->pg_inv_wq = alloc_workqueue("ceph-pg-invalid", 0, 1);
 	if (fsc->pg_inv_wq == NULL)
 		goto fail_wb_wq;
-	fsc->trunc_wq = create_singlethread_workqueue("ceph-trunc");
+	fsc->trunc_wq = alloc_workqueue("ceph-trunc", 0, 1);
 	if (fsc->trunc_wq == NULL)
 		goto fail_pg_inv_wq;