From c4140cbf35b90422be6589024f47e132eb2298b1 Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@suse.com>
Date: Thu, 4 Apr 2019 14:45:37 +0800
Git-commit: c4140cbf35b90422be6589024f47e132eb2298b1
References: bsc#1063638 bsc#1128052 bsc#1108838
Patch-mainline: v5.2-rc1
Subject: [PATCH 9/9] btrfs: qgroup: Don't scan leaf if we're modifying reloc
 tree

Since reloc tree doesn't contribute to qgroup numbers, just skip them.

This should catch the final cause of unnecessary data ref processing
when running balance of metadata with qgroups on.

The 4G data 16 snapshots test (*) should explain it pretty well:

             | delayed subtree | refactor delayed ref | this patch
---------------------------------------------------------------------
relocated    |           22653 |                22673 |         22744
qgroup dirty |          122792 |                48360 |            70
time         |          24.494 |               11.606 |         3.944

Finally, we're at the stage where qgroup + metadata balance cost no
obvious overhead.

Test environment:

Test VM:
- vRAM		8G
- vCPU		8
- block dev	vitrio-blk, 'unsafe' cache mode
- host block	850evo

Test workload:
- Copy 4G data from /usr/ to one subvolume
- Create 16 snapshots of that subvolume, and modify 3 files in each
  snapshot
- Enable quota, rescan
- Time "btrfs balance start -m"

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/extent-tree.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8911,11 +8911,14 @@ static noinline int walk_up_proc(struct
 			else
 				ret = btrfs_dec_ref(trans, root, eb, 0);
 			BUG_ON(ret); /* -ENOMEM */
-			ret = btrfs_qgroup_trace_leaf_items(trans, fs_info, eb);
-			if (ret) {
-				btrfs_err_rl(fs_info,
-					     "error %d accounting leaf items. Quota is out of sync, rescan required.",
-					     ret);
+			if (is_fstree(root->root_key.objectid)) {
+				ret = btrfs_qgroup_trace_leaf_items(trans,
+						fs_info, eb);
+				if (ret) {
+					btrfs_err_rl(fs_info,
+"error %d accounting leaf items. Quota is out of sync, rescan required.",
+						     ret);
+				}
 			}
 		}
 		/* make block locked assertion in clean_tree_block happy */