From b0319c1faae5a77e553ae74bf899efbc6629674d Mon Sep 17 00:00:00 2001
From: Brian Behlendorf <behlendorf1@llnl.gov>
Date: Thu, 1 Dec 2016 16:50:11 -0700
Subject: [PATCH] OpenZFS 7143 - dbuf_read() creates unnecessary zio_root() for
bonus buf
dbuf_read() creates a zio_root() to track and wait for all the
zio's that may happen as part of this call. However, if the blkptr_t
for this buffer is NULL or a hole, we will not create any more zio's,
so this zio_root() is unnecessary. This is always the case when calling
dbuf_read() on a bonus buffer, because it has no blkptr (it's part of
the containing dnode). For workloads that read a lot of bonus buffers
(e.g. file creation and removal), creating and destroying these
unnecessary zio's can decrease performance by around 3%.
The fix is to only create/destroy the zio_root() in dbuf_read() if
the blkptr is not NULL and not a hole.
Changes sponsored by Intel Corp.
Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue openzfs/openzfs#137
Closes #4803
Closes #5382
---
module/zfs/dbuf.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index f7857134c8..cfa4fd1fc7 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -21,7 +21,7 @@
/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright 2011 Nexenta Systems, Inc. All rights reserved.
- * Copyright (c) 2012, 2016 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
* Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
* Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
*/
@@ -1207,7 +1207,8 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
} else if (db->db_state == DB_UNCACHED) {
spa_t *spa = dn->dn_objset->os_spa;
- if (zio == NULL)
+ if (zio == NULL &&
+ db->db_blkptr != NULL && !BP_IS_HOLE(db->db_blkptr))
zio = zio_root(spa, NULL, NULL, ZIO_FLAG_CANFAIL);
err = dbuf_read_impl(db, zio, flags);
@@ -1221,7 +1222,7 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
rw_exit(&dn->dn_struct_rwlock);
DB_DNODE_EXIT(db);
- if (!err && !havepzio)
+ if (!err && !havepzio && zio != NULL)
err = zio_wait(zio);
} else {
/*