Illumos 4873 - zvol unmap calls can take a very long time for larger datasets

4873 zvol unmap calls can take a very long time for larger datasets
Author: Alex Reece <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Paul Dagnelie <[email protected]>
Reviewed by: Basil Crow <[email protected]>
Reviewed by: Dan McDonald <[email protected]>
Approved by: Robert Mustacchi <[email protected]>

References:
  https://www.illumos.org/issues/4873
  https://github.com/illumos/illumos-gate/commit/0f6d88a

Porting Notes:

dbuf_free_range():
  - reduce stack usage using kmem_alloc()
  - the sorted AVL tree will handle the spill block case correctly
    without all the special handling in the for() loop

Ported-by: Chris Dunlop <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 41 insertions, 27 deletions

diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index f5327a34a..e9c8580fc 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -93,7 +93,9 @@ dbuf_cons(void *vdb, void *unused, int kmflag)
 	mutex_init(&db->db_mtx, NULL, MUTEX_DEFAULT, NULL);
 	cv_init(&db->db_changed, NULL, CV_DEFAULT, NULL);
 	refcount_create(&db->db_holds);
-	list_link_init(&db->db_link);
+
+	db->db_creation = gethrtime();
+
 	return (0);
 }
 
@@ -386,7 +388,7 @@ dbuf_verify(dmu_buf_impl_t *db)
 		ASSERT3U(db->db_level, <, dn->dn_nlevels);
 		ASSERT(db->db_blkid == DMU_BONUS_BLKID ||
 		    db->db_blkid == DMU_SPILL_BLKID ||
-		    !list_is_empty(&dn->dn_dbufs));
+		    !avl_is_empty(&dn->dn_dbufs));
 	}
 	if (db->db_blkid == DMU_BONUS_BLKID) {
 		ASSERT(dn != NULL);
@@ -866,23 +868,34 @@ dbuf_unoverride(dbuf_dirty_record_t *dr)
  * receive; see comment below for details.
  */
 void
-dbuf_free_range(dnode_t *dn, uint64_t start, uint64_t end, dmu_tx_t *tx)
+dbuf_free_range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
+    dmu_tx_t *tx)
 {
-	dmu_buf_impl_t *db, *db_next;
+	dmu_buf_impl_t *db, *db_next, *db_search;
 	uint64_t txg = tx->tx_txg;
+	avl_index_t where;
 	boolean_t freespill =
-	    (start == DMU_SPILL_BLKID || end == DMU_SPILL_BLKID);
+	    (start_blkid == DMU_SPILL_BLKID || end_blkid == DMU_SPILL_BLKID);
+
+	if (end_blkid > dn->dn_maxblkid && !freespill)
+		end_blkid = dn->dn_maxblkid;
+	dprintf_dnode(dn, "start=%llu end=%llu\n", start_blkid, end_blkid);
 
-	if (end > dn->dn_maxblkid && !freespill)
-		end = dn->dn_maxblkid;
-	dprintf_dnode(dn, "start=%llu end=%llu\n", start, end);
+	db_seach = kmem_alloc(sizeof (dmu_buf_impl_t), KM_SLEEP);
+	db_search->db_level = 0;
+	db_search->db_blkid = start_blkid;
+	db_search->db_creation = 0;
 
 	mutex_enter(&dn->dn_dbufs_mtx);
-	if (start >= dn->dn_unlisted_l0_blkid * dn->dn_datablksz &&
-	    !freespill) {
+	if (start_blkid >= dn->dn_unlisted_l0_blkid && !freespill) {
 		/* There can't be any dbufs in this range; no need to search. */
-		mutex_exit(&dn->dn_dbufs_mtx);
-		return;
+#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
@@ -894,19 +907,18 @@ dbuf_free_range(dnode_t *dn, uint64_t start, uint64_t end, dmu_tx_t *tx)
 		atomic_inc_64(&zfs_free_range_recv_miss);
 	}
 
-	for (db = list_head(&dn->dn_dbufs); db != NULL; db = db_next) {
-		db_next = list_next(&dn->dn_dbufs, db);
+	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) {
+		db_next = AVL_NEXT(&dn->dn_dbufs, db);
 		ASSERT(db->db_blkid != DMU_BONUS_BLKID);
 
-		/* Skip indirect blocks. */
-		if (db->db_level != 0)
-			continue;
-		/* Skip direct blocks outside the range. */
-		if (!freespill && (db->db_blkid < start || db->db_blkid > end))
-			continue;
-		/* Skip all direct blocks, only free spill blocks. */
-		if (freespill && (db->db_blkid != DMU_SPILL_BLKID))
-			continue;
+		if (db->db_level != 0 || db->db_blkid > end_blkid) {
+			break;
+		}
+		ASSERT3U(db->db_blkid, >=, start_blkid);
 
 		/* found a level 0 buffer in the range */
 		mutex_enter(&db->db_mtx);
@@ -968,6 +980,9 @@ dbuf_free_range(dnode_t *dn, uint64_t start, uint64_t end, dmu_tx_t *tx)
 
 		mutex_exit(&db->db_mtx);
 	}
+
+out:
+	kmem_free(db_search, sizeof (dmu_buf_impl_t));
 	mutex_exit(&dn->dn_dbufs_mtx);
 }
 
@@ -1657,7 +1672,7 @@ dbuf_clear(dmu_buf_impl_t *db)
 	dn = DB_DNODE(db);
 	dndb = dn->dn_dbuf;
 	if (db->db_blkid != DMU_BONUS_BLKID && MUTEX_HELD(&dn->dn_dbufs_mtx)) {
-		list_remove(&dn->dn_dbufs, db);
+		avl_remove(&dn->dn_dbufs, db);
 		atomic_dec_32(&dn->dn_dbufs_count);
 		membar_producer();
 		DB_DNODE_EXIT(db);
@@ -1829,7 +1844,7 @@ dbuf_create(dnode_t *dn, uint8_t level, uint64_t blkid,
 		mutex_exit(&dn->dn_dbufs_mtx);
 		return (odb);
 	}
-	list_insert_head(&dn->dn_dbufs, db);
+	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;
@@ -1888,7 +1903,7 @@ dbuf_destroy(dmu_buf_impl_t *db)
 			DB_DNODE_ENTER(db);
 			dn = DB_DNODE(db);
 			mutex_enter(&dn->dn_dbufs_mtx);
-			list_remove(&dn->dn_dbufs, db);
+			avl_remove(&dn->dn_dbufs, db);
 			atomic_dec_32(&dn->dn_dbufs_count);
 			mutex_exit(&dn->dn_dbufs_mtx);
 			DB_DNODE_EXIT(db);
@@ -1906,7 +1921,6 @@ dbuf_destroy(dmu_buf_impl_t *db)
 	db->db_parent = NULL;
 	db->db_buf = NULL;
 
-	ASSERT(!list_link_active(&db->db_link));
 	ASSERT(db->db.db_data == NULL);
 	ASSERT(db->db_hash_next == NULL);
 	ASSERT(db->db_blkptr == NULL);