4045 zfs write throttle & i/o scheduler performance work
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>

@@ -308,11 +308,11 @@
                 mutex_exit(&vc->vc_lock);
                 return (SET_ERROR(ENOMEM));
         }
 
         fio = zio_vdev_delegated_io(zio->io_vd, cache_offset,
-            ve->ve_data, VCBS, ZIO_TYPE_READ, ZIO_PRIORITY_CACHE_FILL,
+            ve->ve_data, VCBS, ZIO_TYPE_READ, ZIO_PRIORITY_NOW,
             ZIO_FLAG_DONT_CACHE, vdev_cache_fill, ve);
 
         ve->ve_fill_io = fio;
         zio_vdev_io_bypass(zio);
         zio_add_child(zio, fio);