MFC r268859: MFV r268851:

When a sync task is waiting for a txg to complete, we should hurry it along
by increasing the number of outstanding async writes (i.e. make
vdev_queue_max_async_writes() return a larger number).

Illumos issue:
    4753 increase number of outstanding async writes when sync task is waiting

1 files changed, 12 insertions, 4 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c
index 11f05a0..c62c97d 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c
@@ -24,7 +24,7 @@
  */
 
 /*
- * Copyright (c) 2013 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
  */
 
 #include <sys/zfs_context.h>
@@ -408,14 +408,23 @@ vdev_queue_class_min_active(zio_priority_t p)
 }
 
 static int
-vdev_queue_max_async_writes(uint64_t dirty)
+vdev_queue_max_async_writes(spa_t *spa)
 {
 	int writes;
+	uint64_t dirty = spa->spa_dsl_pool->dp_dirty_total;
 	uint64_t min_bytes = zfs_dirty_data_max *
 	    zfs_vdev_async_write_active_min_dirty_percent / 100;
 	uint64_t max_bytes = zfs_dirty_data_max *
 	    zfs_vdev_async_write_active_max_dirty_percent / 100;
 
+	/*
+	 * Sync tasks correspond to interactive user actions. To reduce the
+	 * execution time of those actions we push data out as fast as possible.
+	 */
+	if (spa_has_pending_synctask(spa)) {
+		return (zfs_vdev_async_write_max_active);
+	}
+
 	if (dirty < min_bytes)
 		return (zfs_vdev_async_write_min_active);
 	if (dirty > max_bytes)
@@ -448,8 +457,7 @@ vdev_queue_class_max_active(spa_t *spa, zio_priority_t p)
 	case ZIO_PRIORITY_ASYNC_READ:
 		return (zfs_vdev_async_read_max_active);
 	case ZIO_PRIORITY_ASYNC_WRITE:
-		return (vdev_queue_max_async_writes(
-		    spa->spa_dsl_pool->dp_dirty_total));
+		return (vdev_queue_max_async_writes(spa));
 	case ZIO_PRIORITY_SCRUB:
 		return (zfs_vdev_scrub_max_active);
 	default: