Provide more flexible object allocation interface

Object allocation performance can be improved for complex operations
by providing an interface which returns the newly allocated dnode.
This allows the caller to immediately use the dnode without incurring
the expense of looking up the dnode by object number.

The functions dmu_object_alloc_hold(), zap_create_hold(), and
dmu_bonus_hold_by_dnode() were added for this purpose.

The zap_create_* functions have been updated to take advantage of
this new functionality.  The dmu_bonus_hold_impl() function should
really have never been included in sys/dmu.h and was removed.
It's sole caller was converted to use dmu_bonus_hold_by_dnode().

The new symbols have been exported for use by Lustre.

Reviewed-by: Tony Hutter <[email protected]>
Reviewed by: Matt Ahrens <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #8015 

1 files changed, 45 insertions, 9 deletions

diff --git a/module/zfs/dmu_object.c b/module/zfs/dmu_object.c
index 9b5cf125f..e77ebeca5 100644
--- a/module/zfs/dmu_object.c
+++ b/module/zfs/dmu_object.c
@@ -44,7 +44,7 @@ int dmu_object_alloc_chunk_shift = 7;
 static uint64_t
 dmu_object_alloc_impl(objset_t *os, dmu_object_type_t ot, int blocksize,
     int indirect_blockshift, dmu_object_type_t bonustype, int bonuslen,
-    int dnodesize, dmu_tx_t *tx)
+    int dnodesize, dnode_t **allocated_dnode, void *tag, dmu_tx_t *tx)
 {
 	uint64_t object;
 	uint64_t L1_dnode_count = DNODES_PER_BLOCK <<
@@ -80,6 +80,19 @@ dmu_object_alloc_impl(objset_t *os, dmu_object_type_t ot, int blocksize,
 	if (dnodes_per_chunk > L1_dnode_count)
 		dnodes_per_chunk = L1_dnode_count;
 
+	/*
+	 * The caller requested the dnode be returned as a performance
+	 * optimization in order to avoid releasing the hold only to
+	 * immediately reacquire it.  Since they caller is responsible
+	 * for releasing the hold they must provide the tag.
+	 */
+	if (allocated_dnode != NULL) {
+		ASSERT3P(tag, !=, NULL);
+	} else {
+		ASSERT3P(tag, ==, NULL);
+		tag = FTAG;
+	}
+
 	object = *cpuobj;
 	for (;;) {
 		/*
@@ -167,7 +180,7 @@ dmu_object_alloc_impl(objset_t *os, dmu_object_type_t ot, int blocksize,
 		 * to do so.
 		 */
 		error = dnode_hold_impl(os, object, DNODE_MUST_BE_FREE,
-		    dn_slots, FTAG, &dn);
+		    dn_slots, tag, &dn);
 		if (error == 0) {
 			rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
 			/*
@@ -180,11 +193,20 @@ dmu_object_alloc_impl(objset_t *os, dmu_object_type_t ot, int blocksize,
 				    bonuslen, dn_slots, tx);
 				rw_exit(&dn->dn_struct_rwlock);
 				dmu_tx_add_new_object(tx, dn);
-				dnode_rele(dn, FTAG);
+
+				/*
+				 * Caller requested the allocated dnode be
+				 * returned and is responsible for the hold.
+				 */
+				if (allocated_dnode != NULL)
+					*allocated_dnode = dn;
+				else
+					dnode_rele(dn, tag);
+
 				return (object);
 			}
 			rw_exit(&dn->dn_struct_rwlock);
-			dnode_rele(dn, FTAG);
+			dnode_rele(dn, tag);
 			DNODE_STAT_BUMP(dnode_alloc_race);
 		}
 
@@ -205,7 +227,7 @@ dmu_object_alloc(objset_t *os, dmu_object_type_t ot, int blocksize,
     dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
 {
 	return dmu_object_alloc_impl(os, ot, blocksize, 0, bonustype,
-	    bonuslen, 0, tx);
+	    bonuslen, 0, NULL, NULL, tx);
 }
 
 uint64_t
@@ -214,7 +236,7 @@ dmu_object_alloc_ibs(objset_t *os, dmu_object_type_t ot, int blocksize,
     dmu_tx_t *tx)
 {
 	return dmu_object_alloc_impl(os, ot, blocksize, indirect_blockshift,
-	    bonustype, bonuslen, 0, tx);
+	    bonustype, bonuslen, 0, NULL, NULL, tx);
 }
 
 uint64_t
@@ -222,7 +244,21 @@ dmu_object_alloc_dnsize(objset_t *os, dmu_object_type_t ot, int blocksize,
     dmu_object_type_t bonustype, int bonuslen, int dnodesize, dmu_tx_t *tx)
 {
 	return (dmu_object_alloc_impl(os, ot, blocksize, 0, bonustype,
-	    bonuslen, dnodesize, tx));
+	    bonuslen, dnodesize, NULL, NULL, tx));
+}
+
+/*
+ * Allocate a new object and return a pointer to the newly allocated dnode
+ * via the allocated_dnode argument.  The returned dnode will be held and
+ * the caller is responsible for releasing the hold by calling dnode_rele().
+ */
+uint64_t
+dmu_object_alloc_hold(objset_t *os, dmu_object_type_t ot, int blocksize,
+    int indirect_blockshift, dmu_object_type_t bonustype, int bonuslen,
+    int dnodesize, dnode_t **allocated_dnode, void *tag, dmu_tx_t *tx)
+{
+	return (dmu_object_alloc_impl(os, ot, blocksize, indirect_blockshift,
+	    bonustype, bonuslen, dnodesize, allocated_dnode, tag, tx));
 }
 
 int
@@ -414,14 +450,13 @@ dmu_object_zapify(objset_t *mos, uint64_t object, dmu_object_type_t old_type,
 	 * so that concurrent calls to *_is_zapified() can determine if
 	 * the object has been completely zapified by checking the type.
 	 */
-	mzap_create_impl(mos, object, 0, 0, tx);
+	mzap_create_impl(dn, 0, 0, tx);
 
 	dn->dn_next_type[tx->tx_txg & TXG_MASK] = dn->dn_type =
 	    DMU_OTN_ZAP_METADATA;
 	dnode_setdirty(dn, tx);
 	dnode_rele(dn, FTAG);
 
-
 	spa_feature_incr(dmu_objset_spa(mos),
 	    SPA_FEATURE_EXTENSIBLE_DATASET, tx);
 }
@@ -449,6 +484,7 @@ dmu_object_free_zapified(objset_t *mos, uint64_t object, dmu_tx_t *tx)
 EXPORT_SYMBOL(dmu_object_alloc);
 EXPORT_SYMBOL(dmu_object_alloc_ibs);
 EXPORT_SYMBOL(dmu_object_alloc_dnsize);
+EXPORT_SYMBOL(dmu_object_alloc_hold);
 EXPORT_SYMBOL(dmu_object_claim);
 EXPORT_SYMBOL(dmu_object_claim_dnsize);
 EXPORT_SYMBOL(dmu_object_reclaim);