[PATCH] btrfs: Batch up release of delayed inode metadata

[Nikolay Borisov <nborisov@suse.com>]

With Filipe's recent rework of the delayed inode code one aspect which
isn't batched is the release of the reserved metadata of delayed inode's
delete items. With this batch on top of his rework I see the following
change of the number of calls to btrfs_block_rsv_release:

Before this change:
@block_rsv_release: 1004
@btrfs_delete_delayed_items_total_time: 14602
@delete_batches: 505

After:
@block_rsv_release: 510
@btrfs_delete_delayed_items_total_time: 13643
@delete_batches: 507

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/delayed-inode.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index e1e856436ad5..6c06ddba5a7a 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -800,11 +800,13 @@ static int btrfs_batch_delete_items(struct btrfs_trans_handle *trans,
 				    struct btrfs_path *path,
 				    struct btrfs_delayed_item *item)
 {
+	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct btrfs_delayed_item *curr, *next;
 	struct extent_buffer *leaf = path->nodes[0];
 	LIST_HEAD(batch_list);
 	int nitems, slot, last_slot;
 	int ret;
+	u64 total_reserved_size = item->bytes_reserved;
 
 	ASSERT(leaf != NULL);
 
@@ -841,14 +843,23 @@ static int btrfs_batch_delete_items(struct btrfs_trans_handle *trans,
 		nitems++;
 		curr = next;
 		list_add_tail(&curr->tree_list, &batch_list);
+		total_reserved_size += curr->bytes_reserved;
 	}
 
 	ret = btrfs_del_items(trans, root, path, path->slots[0], nitems);
 	if (ret)
 		return ret;
 
+	/*
+	 * Check btrfs_delayed_item_reserve_metadata() to see why we don't need
+	 * to release/reserve qgroup space.
+	 */
+	trace_btrfs_space_reservation(fs_info, "delayed_item", 0,
+				      total_reserved_size, 0);
+	btrfs_block_rsv_release(fs_info, &fs_info->delayed_block_rsv,
+				total_reserved_size, NULL);
+
 	list_for_each_entry_safe(curr, next, &batch_list, tree_list) {
-		btrfs_delayed_item_release_metadata(root, curr);
 		list_del(&curr->tree_list);
 		btrfs_release_delayed_item(curr);
 	}
-- 
2.25.1