OpenZFS 7968 - multi-threaded spa_sync()

Reviewed by: Pavel Zakharov <[email protected]>
Reviewed by: Brad Lewis <[email protected]>
Reviewed by: Saso Kiselkov <[email protected]>
Reviewed by: Brian Behlendorf <[email protected]>
Ported-by: Matthew Ahrens <[email protected]>

spa_sync() iterates over all the dirty dnodes and processes each of them
by calling dnode_sync(). If there are many dirty dnodes (e.g. because we
created or removed a lot of files), the single thread of spa_sync()
calling dnode_sync() can become a bottleneck. Additionally, if many
dnodes are dirtied concurrently in open context (e.g. due to concurrent
file creation), the os_lock will experience lock contention via
dnode_setdirty().

The solution is to track dirty dnodes on a multilist_t, and for
spa_sync() to use separate threads to process each of the sublists in
the multilist.

OpenZFS-issue: https://www.illumos.org/issues/7968
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/4a2a54c
Closes #5752 

1 files changed, 9 insertions, 9 deletions

diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index f11a11ff1..ce99fd54c 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, 2015 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2017 by Delphix. All rights reserved.
  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  */
@@ -104,7 +104,7 @@ static boolean_t dbuf_evict_thread_exit;
  * Dbufs that are aged out of the cache will be immediately destroyed and
  * become eligible for arc eviction.
  */
-static multilist_t dbuf_cache;
+static multilist_t *dbuf_cache;
 static refcount_t dbuf_cache_size;
 unsigned long  dbuf_cache_max_bytes = 100 * 1024 * 1024;
 
@@ -491,8 +491,8 @@ dbuf_cache_above_lowater(void)
 static void
 dbuf_evict_one(void)
 {
-	int idx = multilist_get_random_index(&dbuf_cache);
-	multilist_sublist_t *mls = multilist_sublist_lock(&dbuf_cache, idx);
+	int idx = multilist_get_random_index(dbuf_cache);
+	multilist_sublist_t *mls = multilist_sublist_lock(dbuf_cache, idx);
 	dmu_buf_impl_t *db;
 	ASSERT(!MUTEX_HELD(&dbuf_evict_lock));
 
@@ -671,7 +671,7 @@ retry:
 	 */
 	dbu_evict_taskq = taskq_create("dbu_evict", 1, defclsyspri, 0, 0, 0);
 
-	multilist_create(&dbuf_cache, sizeof (dmu_buf_impl_t),
+	dbuf_cache = multilist_create(sizeof (dmu_buf_impl_t),
 	    offsetof(dmu_buf_impl_t, db_cache_link),
 	    dbuf_cache_multilist_index_func);
 	refcount_create(&dbuf_cache_size);
@@ -719,7 +719,7 @@ dbuf_fini(void)
 	cv_destroy(&dbuf_evict_cv);
 
 	refcount_destroy(&dbuf_cache_size);
-	multilist_destroy(&dbuf_cache);
+	multilist_destroy(dbuf_cache);
 }
 
 /*
@@ -2120,7 +2120,7 @@ dbuf_destroy(dmu_buf_impl_t *db)
 	dbuf_clear_data(db);
 
 	if (multilist_link_active(&db->db_cache_link)) {
-		multilist_remove(&dbuf_cache, db);
+		multilist_remove(dbuf_cache, db);
 		(void) refcount_remove_many(&dbuf_cache_size,
 		    db->db.db_size, db);
 	}
@@ -2690,7 +2690,7 @@ __dbuf_hold_impl(struct dbuf_hold_impl_data *dh)
 
 	if (multilist_link_active(&dh->dh_db->db_cache_link)) {
 		ASSERT(refcount_is_zero(&dh->dh_db->db_holds));
-		multilist_remove(&dbuf_cache, dh->dh_db);
+		multilist_remove(dbuf_cache, dh->dh_db);
 		(void) refcount_remove_many(&dbuf_cache_size,
 		    dh->dh_db->db.db_size, dh->dh_db);
 	}
@@ -2962,7 +2962,7 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
 			    db->db_pending_evict) {
 				dbuf_destroy(db);
 			} else if (!multilist_link_active(&db->db_cache_link)) {
-				multilist_insert(&dbuf_cache, db);
+				multilist_insert(dbuf_cache, db);
 				(void) refcount_add_many(&dbuf_cache_size,
 				    db->db.db_size, db);
 				mutex_exit(&db->db_mtx);