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.
[[Benchmark]]
Hardware:
VM 4G vRAM, 8 vCPUs,
disk is using 'unsafe' cache mode,
backing device is SAMSUNG 850 evo SSD.
Host has 16G ram.
Mkfs parameter:
--nodesize 4K (To bump up tree size)
Initial subvolume contents:
4G data copied from /usr and /lib.
(With enough regular small files)
Snapshots:
16 snapshots of the original subvolume.
each snapshot has 3 random files modified.
balance parameter:
-m
So the content should be pretty similar to a real world root fs layout.
| v4.19-rc1 | w/ patchset | diff (*)
---------------------------------------------------------------
relocated extents | 22929 | 22900 | -0.1%
qgroup dirty extents | 227757 | 167139 | -26.6%
time (sys) | 65.253s | 50.123s | -23.2%
time (real) | 74.032s | 52.551s | -29.0%
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
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..028d1a80d36f 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) {
+ /*
+ * 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) {
--
2.19.0
