[PATCH] btrfs: qgroup: Don't trace subtree if we're dropping tree reloc tree

[Qu Wenruo <wqu@suse.com>]

Tree reloc tree doesn't contribute to qgroup numbers, as we have
accounted them at balance time (check replace_path()).

Skip such unneeded subtree trace should reduce some performance
overhead.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent-tree.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index de6f75f5547b..4588153f414c 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8643,7 +8643,13 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
 			parent = 0;
 		}
 
-		if (need_account) {
+		/*
+		 * Tree reloc tree doesn't contribute to qgroup numbers, and
+		 * we have already accounted them at merge time (replace_path),
+		 * thus we could skip expensive subtree trace here.
+		 */
+		if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID &&
+		    need_account) {
 			ret = btrfs_qgroup_trace_subtree(trans, next,
 							 generation, level - 1);
 			if (ret) {
-- 
2.18.0