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

5 files changed, 44 insertions, 6 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_misc.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_misc.c
index d09fb5b..21904490 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_misc.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_misc.c
@@ -1938,6 +1938,16 @@ spa_writeable(spa_t *spa)
 	return (!!(spa->spa_mode & FWRITE));
 }
 
+/*
+ * Returns true if there is a pending sync task in any of the current
+ * syncing txg, the current quiescing txg, or the current open txg.
+ */
+boolean_t
+spa_has_pending_synctask(spa_t *spa)
+{
+	return (!txg_all_lists_empty(&spa->spa_dsl_pool->dp_sync_tasks));
+}
+
 int
 spa_mode(spa_t *spa)
 {
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa.h
index 9755f29..f62e315 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa.h
@@ -800,6 +800,7 @@ extern uint64_t bp_get_dsize(spa_t *spa, const blkptr_t *bp);
 extern boolean_t spa_has_slogs(spa_t *spa);
 extern boolean_t spa_is_root(spa_t *spa);
 extern boolean_t spa_writeable(spa_t *spa);
+extern boolean_t spa_has_pending_synctask(spa_t *spa);
 
 extern int spa_mode(spa_t *spa);
 extern uint64_t zfs_strtonum(const char *str, char **nptr);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/txg.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/txg.h
index e96c1fa..77e2dba2 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/txg.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/txg.h
@@ -23,7 +23,7 @@
  * Use is subject to license terms.
  */
 /*
- * Copyright (c) 2013 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
  */
 
 #ifndef _SYS_TXG_H
@@ -112,6 +112,7 @@ extern boolean_t txg_sync_waiting(struct dsl_pool *dp);
 extern void txg_list_create(txg_list_t *tl, size_t offset);
 extern void txg_list_destroy(txg_list_t *tl);
 extern boolean_t txg_list_empty(txg_list_t *tl, uint64_t txg);
+extern boolean_t txg_all_lists_empty(txg_list_t *tl);
 extern boolean_t txg_list_add(txg_list_t *tl, void *p, uint64_t txg);
 extern boolean_t txg_list_add_tail(txg_list_t *tl, void *p, uint64_t txg);
 extern void *txg_list_remove(txg_list_t *tl, uint64_t txg);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c
index 0201bef..83c6b5f76 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c
@@ -21,7 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright 2011 Martin Matuska <mm@FreeBSD.org>
- * Copyright (c) 2013 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
  */
 
 #include <sys/zfs_context.h>
@@ -727,6 +727,24 @@ txg_list_empty(txg_list_t *tl, uint64_t txg)
 }
 
 /*
+ * Returns true if all txg lists are empty.
+ *
+ * Warning: this is inherently racy (an item could be added immediately after this
+ * function returns). We don't bother with the lock because it wouldn't change the
+ * semantics.
+ */
+boolean_t
+txg_all_lists_empty(txg_list_t *tl)
+{
+	for (int i = 0; i < TXG_SIZE; i++) {
+		if (!txg_list_empty(tl, i)) {
+			return (B_FALSE);
+		}
+	}
+	return (B_TRUE);
+}
+
+/*
  * Add an entry to the list (unless it's already on the list).
  * Returns B_TRUE if it was actually added.
  */
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: