On Thu, May 7, 2020 at 4:27 AM robbieko <robbieko@xxxxxxxxxxxx> wrote:
>
> From: Robbie Ko <robbieko@xxxxxxxxxxxx>
>
> When mounting, we handle deleted subvol and orphan items.
> First, find add orphan roots, then add them to fs_root radix tree.
> Second, in tree-root, process each orphan item, skip if it is dead root.
>
> The original algorithm is based on the list of dead_roots,
> one by one to visit and check whether the objectid is consistent,
> the time complexity is O (n ^ 2).
> When processing 50000 deleted subvols, it takes about 120s.
>
> Because btrfs_find_orphan_roots has already ran before us,
> and added deleted subvol to fs_roots radix tree.
>
> The fs root will only be removed from the fs_roots radix tree
> after the cleaner is processed, and the cleaner will only start
> execution after the mount is complete.
>
> btrfs_orphan_cleanup can be called during the whole filesystem mount
> lifetime, but only "tree root" will be used in this section of code,
> and only mount time will be brought into tree root.
>
> So we can quickly check whether the orphan item is dead root
> through the fs_roots radix tree.
>
> Signed-off-by: Robbie Ko <robbieko@xxxxxxxxxxxx>
"Btrfs : improve the speed of compare orphan item and dead roots with
tree root when mount"
That's a really long subject and confusing - compare orphan item? All
we do is check whether a root is dead or not.
So I would suggest some shorter and clear:
"Btrfs: speedup dead root detection during orphan cleanup"
Other than that, looks good, thanks.
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
> ---
> Changes in v2:
> - update changelog
> ---
> fs/btrfs/inode.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 320d1062068d..1becf5c63e5a 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -3000,18 +3000,16 @@ int btrfs_orphan_cleanup(struct btrfs_root *root)
> * orphan must not get deleted.
> * find_dead_roots already ran before us, so if this
> * is a snapshot deletion, we should find the root
> - * in the dead_roots list
> + * in the fs_roots radix tree.
> */
> - spin_lock(&fs_info->trans_lock);
> - list_for_each_entry(dead_root, &fs_info->dead_roots,
> - root_list) {
> - if (dead_root->root_key.objectid ==
> - found_key.objectid) {
> - is_dead_root = 1;
> - break;
> - }
> - }
> - spin_unlock(&fs_info->trans_lock);
> +
> + spin_lock(&fs_info->fs_roots_radix_lock);
> + dead_root = radix_tree_lookup(&fs_info->fs_roots_radix,
> + (unsigned long)found_key.objectid);
> + if (dead_root && btrfs_root_refs(&dead_root->root_item) == 0)
> + is_dead_root = 1;
> + spin_unlock(&fs_info->fs_roots_radix_lock);
> +
> if (is_dead_root) {
> /* prevent this orphan from being found again */
> key.offset = found_key.objectid - 1;
> --
> 2.17.1
>
--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
