btrfs: remove num_entries atomic counter from delayed ref root

The atomic counter 'num_entries' is not used anymore, we increment it
and decrement it but then we don't ever read it to use for any logic.
Its last use was removed with commit 61a56a9 ("btrfs: delayed refs
pre-flushing should only run the heads we have"). So remove it.

Reviewed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/delayed-ref.c

@@ -463,7 +463,6 @@ static inline void drop_delayed_ref(struct btrfs_fs_info *fs_info,
 	if (!list_empty(&ref->add_list))
 		list_del(&ref->add_list);
 	btrfs_put_delayed_ref(ref);
-	atomic_dec(&delayed_refs->num_entries);
 	btrfs_delayed_refs_rsv_release(fs_info, 1, 0);
 }
 
@@ -604,7 +603,6 @@ void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs,
 
 	rb_erase_cached(&head->href_node, &delayed_refs->href_root);
 	RB_CLEAR_NODE(&head->href_node);
-	atomic_dec(&delayed_refs->num_entries);
 	delayed_refs->num_heads--;
 	if (!head->processing)
 		delayed_refs->num_heads_ready--;
@@ -630,7 +628,6 @@ static bool insert_delayed_ref(struct btrfs_trans_handle *trans,
 	if (!exist) {
 		if (ref->action == BTRFS_ADD_DELAYED_REF)
 			list_add_tail(&ref->add_list, &href->ref_add_list);
-		atomic_inc(&root->num_entries);
 		spin_unlock(&href->lock);
 		trans->delayed_ref_updates++;
 		return false;
@@ -901,7 +898,6 @@ add_delayed_ref_head(struct btrfs_trans_handle *trans,
 		}
 		delayed_refs->num_heads++;
 		delayed_refs->num_heads_ready++;
-		atomic_inc(&delayed_refs->num_entries);
 	}
 	if (qrecord_inserted_ret)
 		*qrecord_inserted_ret = qrecord_inserted;

fs/btrfs/delayed-ref.h

@@ -216,11 +216,6 @@ struct btrfs_delayed_ref_root {
 	/* this spin lock protects the rbtree and the entries inside */
 	spinlock_t lock;
 
-	/* how many delayed ref updates we've queued, used by the
-	 * throttling code
-	 */
-	atomic_t num_entries;
-
 	/* total number of head nodes in tree */
 	unsigned long num_heads;
 

fs/btrfs/extent-tree.c

@@ -2029,7 +2029,6 @@ static int btrfs_run_delayed_refs_for_head(struct btrfs_trans_handle *trans,
 		default:
 			WARN_ON(1);
 		}
-		atomic_dec(&delayed_refs->num_entries);
 
 		/*
 		 * Record the must_insert_reserved flag before we drop the

fs/btrfs/transaction.c

@@ -351,7 +351,6 @@ static noinline int join_transaction(struct btrfs_fs_info *fs_info,
 
 	cur_trans->delayed_refs.href_root = RB_ROOT_CACHED;
 	xa_init(&cur_trans->delayed_refs.dirty_extents);
-	atomic_set(&cur_trans->delayed_refs.num_entries, 0);
 
 	/*
 	 * although the tree mod log is per file system and not per transaction,