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

Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed by: Adam Leventhal <[email protected]>
Reviewed by: Christopher Siden <[email protected]>
Reviewed by: Dan McDonald <[email protected]>
Approved by: Garrett D'Amore <[email protected]>

References:
    https://www.illumos.org/issues/4753
    https://github.com/illumos/illumos-gate/commit/73527f4

Comments by Matt Ahrens from the issue tracker:
    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).
    Initially we might just have a tunable for "minimum async writes
    while a synctask is waiting" and set it to 3.

Ported-by: Tim Chase <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2716

1 files changed, 21 insertions, 1 deletions

diff --git a/module/zfs/txg.c b/module/zfs/txg.c
index a39732bb9..a10261846 100644
--- a/module/zfs/txg.c
+++ b/module/zfs/txg.c
@@ -21,7 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright 2011 Martin Matuska
- * Copyright (c) 2013 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
  */
 
 #include <sys/zfs_context.h>
@@ -787,6 +787,26 @@ 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)
+{
+	int i;
+
+	for (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.
  */