OpenZFS 7500 - Simplify dbuf_free_range by removing dn_unlisted_l0_blkid

Authored by: Stephen Blinick <stephen.blinick@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Approved by: Gordon Ross <gordon.w.ross@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/7500
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/653af1b
Closes #5639

include/sys/dnode.h

@@ -236,8 +236,6 @@ struct dnode {
 
 	/* protected by dn_dbufs_mtx; declared here to fill 32-bit hole */
 	uint32_t dn_dbufs_count;	/* count of dn_dbufs */
-	/* There are no level-0 blocks of this blkid or higher in dn_dbufs */
-	uint64_t dn_unlisted_l0_blkid;
 
 	/* protected by os_lock: */
 	list_node_t dn_dirty_link[TXG_SIZE];	/* next on dataset's dirty */

module/zfs/dbuf.c

@@ -74,11 +74,6 @@ static void __dbuf_hold_impl_init(struct dbuf_hold_impl_data *dh,
 static int __dbuf_hold_impl(struct dbuf_hold_impl_data *dh);
 
 uint_t zfs_dbuf_evict_key;
-/*
- * Number of times that zfs_free_range() took the slow path while doing
- * a zfs receive.  A nonzero value indicates a potential performance problem.
- */
-uint64_t zfs_free_range_recv_miss;
 
 static boolean_t dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx);
 static void dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx);
@@ -1340,9 +1335,6 @@ dbuf_unoverride(dbuf_dirty_record_t *dr)
  * Evict (if its unreferenced) or clear (if its referenced) any level-0
  * data blocks in the free range, so that any future readers will find
  * empty blocks.
- *
- * This is a no-op if the dataset is in the middle of an incremental
- * receive; see comment below for details.
  */
 void
 dbuf_free_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
@@ -1352,10 +1344,9 @@ dbuf_free_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
 	dmu_buf_impl_t *db, *db_next;
 	uint64_t txg = tx->tx_txg;
 	avl_index_t where;
-	boolean_t freespill =
-	    (start_blkid == DMU_SPILL_BLKID || end_blkid == DMU_SPILL_BLKID);
 
-	if (end_blkid > dn->dn_maxblkid && !freespill)
+	if (end_blkid > dn->dn_maxblkid &&
+	    !(start_blkid == DMU_SPILL_BLKID || end_blkid == DMU_SPILL_BLKID))
 		end_blkid = dn->dn_maxblkid;
 	dprintf_dnode(dn, "start=%llu end=%llu\n", start_blkid, end_blkid);
 
@@ -1365,28 +1356,9 @@ dbuf_free_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
 	db_search->db_state = DB_SEARCH;
 
 	mutex_enter(&dn->dn_dbufs_mtx);
-	if (start_blkid >= dn->dn_unlisted_l0_blkid && !freespill) {
-		/* There can't be any dbufs in this range; no need to search. */
-#ifdef DEBUG
-		db = avl_find(&dn->dn_dbufs, db_search, &where);
-		ASSERT3P(db, ==, NULL);
-		db = avl_nearest(&dn->dn_dbufs, where, AVL_AFTER);
-		ASSERT(db == NULL || db->db_level > 0);
-#endif
-		goto out;
-	} else if (dmu_objset_is_receiving(dn->dn_objset)) {
-		/*
-		 * If we are receiving, we expect there to be no dbufs in
-		 * the range to be freed, because receive modifies each
-		 * block at most once, and in offset order.  If this is
-		 * not the case, it can lead to performance problems,
-		 * so note that we unexpectedly took the slow path.
-		 */
-		atomic_inc_64(&zfs_free_range_recv_miss);
-	}
-
 	db = avl_find(&dn->dn_dbufs, db_search, &where);
 	ASSERT3P(db, ==, NULL);
+
 	db = avl_nearest(&dn->dn_dbufs, where, AVL_AFTER);
 
 	for (; db != NULL; db = db_next) {
@@ -1459,7 +1431,6 @@ dbuf_free_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
 		mutex_exit(&db->db_mtx);
 	}
 
-out:
 	kmem_free(db_search, sizeof (dmu_buf_impl_t));
 	mutex_exit(&dn->dn_dbufs_mtx);
 }
@@ -2416,9 +2387,7 @@ dbuf_create(dnode_t *dn, uint8_t level, uint64_t blkid,
 		return (odb);
 	}
 	avl_add(&dn->dn_dbufs, db);
-	if (db->db_level == 0 && db->db_blkid >=
+
-	    dn->dn_unlisted_l0_blkid)
-		dn->dn_unlisted_l0_blkid = db->db_blkid + 1;
 	db->db_state = DB_UNCACHED;
 	mutex_exit(&dn->dn_dbufs_mtx);
 	arc_space_consume(sizeof (dmu_buf_impl_t), ARC_SPACE_DBUF);

module/zfs/dnode.c

@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2016 by Delphix. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  */
 
@@ -141,7 +141,6 @@ dnode_cons(void *arg, void *unused, int kmflag)
 	dn->dn_id_flags = 0;
 
 	dn->dn_dbufs_count = 0;
-	dn->dn_unlisted_l0_blkid = 0;
 	avl_create(&dn->dn_dbufs, dbuf_compare, sizeof (dmu_buf_impl_t),
 	    offsetof(dmu_buf_impl_t, db_link));
 
@@ -194,7 +193,6 @@ dnode_dest(void *arg, void *unused)
 	ASSERT0(dn->dn_id_flags);
 
 	ASSERT0(dn->dn_dbufs_count);
-	ASSERT0(dn->dn_unlisted_l0_blkid);
 	avl_destroy(&dn->dn_dbufs);
 }
 
@@ -515,7 +513,6 @@ dnode_destroy(dnode_t *dn)
 	dn->dn_newuid = 0;
 	dn->dn_newgid = 0;
 	dn->dn_id_flags = 0;
-	dn->dn_unlisted_l0_blkid = 0;
 
 	dmu_zfetch_fini(&dn->dn_zfetch);
 	kmem_cache_free(dnode_cache, dn);
@@ -766,7 +763,6 @@ dnode_move_impl(dnode_t *odn, dnode_t *ndn)
 	ASSERT(avl_is_empty(&ndn->dn_dbufs));
 	avl_swap(&ndn->dn_dbufs, &odn->dn_dbufs);
 	ndn->dn_dbufs_count = odn->dn_dbufs_count;
-	ndn->dn_unlisted_l0_blkid = odn->dn_unlisted_l0_blkid;
 	ndn->dn_bonus = odn->dn_bonus;
 	ndn->dn_have_spill = odn->dn_have_spill;
 	ndn->dn_zio = odn->dn_zio;
@@ -799,7 +795,6 @@ dnode_move_impl(dnode_t *odn, dnode_t *ndn)
 	avl_create(&odn->dn_dbufs, dbuf_compare, sizeof (dmu_buf_impl_t),
 	    offsetof(dmu_buf_impl_t, db_link));
 	odn->dn_dbufs_count = 0;
-	odn->dn_unlisted_l0_blkid = 0;
 	odn->dn_bonus = NULL;
 	odn->dn_zfetch.zf_dnode = NULL;