Re: [PATCH] Btrfs: only process as many file extents as there are refs

[Wang Shilong <wangsl.fnst@cn.fujitsu.com>]

On 01/25/2014 03:24 AM, Josef Bacik wrote:
> The backref walking code will search down to the key it is looking for and then
> proceed to walk _all_ of the extents on the file until it hits the end.  This is
> suboptimal with large files, we only need to look for as many extents as we have
> references for that inode.  I have a testcase that creates a randomly written 4
> gig file and before this patch it took 6min 30sec to do the initial send, with
> this patch it takes 2min 30sec to do the intial send.  Thanks,
Make sense, I did a simple test, test time was reduced from 645s to 382s.
(by modifying xfstest btrfs/033, adding more stress!)

Feel free to add:
Tested-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>

>
> Signed-off-by: Josef Bacik <jbacik@fb.com>
> ---
>   fs/btrfs/backref.c | 17 +++++++++--------
>   1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
> index dcf2448..1538496 100644
> --- a/fs/btrfs/backref.c
> +++ b/fs/btrfs/backref.c
> @@ -209,18 +209,19 @@ static int __add_prelim_ref(struct list_head *head, u64 root_id,
>   }
>   
>   static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
> -				struct ulist *parents, int level,
> -				struct btrfs_key *key_for_search, u64 time_seq,
> -				u64 wanted_disk_byte,
> -				const u64 *extent_item_pos)
> +			   struct ulist *parents, struct __prelim_ref *ref,
> +			   int level, u64 time_seq, const u64 *extent_item_pos)
>   {
>   	int ret = 0;
>   	int slot;
>   	struct extent_buffer *eb;
>   	struct btrfs_key key;
> +	struct btrfs_key *key_for_search = &ref->key_for_search;
>   	struct btrfs_file_extent_item *fi;
>   	struct extent_inode_elem *eie = NULL, *old = NULL;
>   	u64 disk_byte;
> +	u64 wanted_disk_byte = ref->wanted_disk_byte;
> +	u64 count = 0;
>   
>   	if (level != 0) {
>   		eb = path->nodes[level];
> @@ -238,7 +239,7 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
>   	if (path->slots[0] >= btrfs_header_nritems(path->nodes[0]))
>   		ret = btrfs_next_old_leaf(root, path, time_seq);
>   
> -	while (!ret) {
> +	while (!ret && count < ref->count) {
>   		eb = path->nodes[0];
>   		slot = path->slots[0];
>   
> @@ -254,6 +255,7 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
>   		if (disk_byte == wanted_disk_byte) {
>   			eie = NULL;
>   			old = NULL;
> +			count++;
>   			if (extent_item_pos) {
>   				ret = check_extent_in_eb(&key, eb, fi,
>   						*extent_item_pos,
> @@ -334,9 +336,8 @@ static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
>   		eb = path->nodes[level];
>   	}
>   
> -	ret = add_all_parents(root, path, parents, level, &ref->key_for_search,
> -				time_seq, ref->wanted_disk_byte,
> -				extent_item_pos);
> +	ret = add_all_parents(root, path, parents, ref, level, time_seq,
> +			      extent_item_pos);
>   out:
>   	path->lowest_level = 0;
>   	btrfs_release_path(path);