From: Alek P <alek-p@users.noreply.github.com>
Date: Fri, 26 May 2017 18:42:10 +0000 (-1000)
Subject: Don't dirty bpobj if it has no entries
X-Git-Tag: zfs-0.7.0-rc5~75
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=9210e43a1660bd1b742e80bfc121b86e2cfad57a;p=zfs

Don't dirty bpobj if it has no entries

In certain cases (dsl_scan_sync() is one), we may end up calling
bpobj_iterate() on an empty bpobj. Even though we don't end up
modifying the bpobj it still gets dirtied, causing unneeded writes
to the pool.

This patch adds an early bail from bpobj_iterate_impl() if bpobj
is empty to prevent unneeded writes.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Alek Pinchuk <apinchuk@datto.com>
Closes #6164
---

diff --git a/module/zfs/bpobj.c b/module/zfs/bpobj.c
index 5f2aff453..82ca94e1d 100644
--- a/module/zfs/bpobj.c
+++ b/module/zfs/bpobj.c
@@ -21,6 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2011, 2016 by Delphix. All rights reserved.
+ * Copyright (c) 2017 Datto Inc.
  */
 
 #include <sys/bpobj.h>
@@ -211,6 +212,9 @@ bpobj_iterate_impl(bpobj_t *bpo, bpobj_itor_t func, void *arg, dmu_tx_t *tx,
 
 	mutex_enter(&bpo->bpo_lock);
 
+	if (!bpobj_hasentries(bpo))
+		goto out;
+
 	if (free)
 		dmu_buf_will_dirty(bpo->bpo_dbuf, tx);