Re: [PATCH v2 2/2] btrfs: incremental send, improve rmdir performance for large directory

[Filipe Manana <fdmanana@gmail.com>]

On Tue, May 8, 2018 at 11:11 AM, robbieko <robbieko@synology.com> wrote:
> From: Robbie Ko <robbieko@synology.com>
>
> Currently when checking if we can delete a directory, we always
> check if all its children have been processed.
>
> Example: A directory with 2,000,000 files was deleted
> Result:
> original : 1994m57.071s
> patch : 1m38.554s
>
> [FIX]
> Instead of checking all children on all calls to can_rmdir(),
> we keep track of the directory index offset of the child last
> checked in the last call to can_rmdir(), and then use it as the
> starting point for future calls to can_rmdir().
>
> Signed-off-by: Robbie Ko <robbieko@synology.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>

> ---
> V2:
>  fix comments
>  split optimization allocations orphan_dir_info
>
>  fs/btrfs/send.c | 31 ++++++++++++++++++++++---------
>  1 file changed, 22 insertions(+), 9 deletions(-)
>
> diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
> index 2830871..a477268 100644
> --- a/fs/btrfs/send.c
> +++ b/fs/btrfs/send.c
> @@ -247,6 +247,7 @@ struct orphan_dir_info {
>         struct rb_node node;
>         u64 ino;
>         u64 gen;
> +       u64 last_dir_index_offset;
>  };
>
>  struct name_cache_entry {
> @@ -2872,6 +2873,7 @@ static int orphanize_inode(struct send_ctx *sctx, u64 ino, u64 gen,
>                 return ERR_PTR(-ENOMEM);
>         odi->ino = dir_ino;
>         odi->gen = 0;
> +       odi->last_dir_index_offset = 0;
>
>         rb_link_node(&odi->node, parent, p);
>         rb_insert_color(&odi->node, &sctx->orphan_dirs);
> @@ -2927,6 +2929,7 @@ static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 dir_gen,
>         struct btrfs_key found_key;
>         struct btrfs_key loc;
>         struct btrfs_dir_item *di;
> +       struct orphan_dir_info *odi = NULL;
>
>         /*
>          * Don't try to rmdir the top/root subvolume dir.
> @@ -2941,6 +2944,11 @@ static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 dir_gen,
>         key.objectid = dir;
>         key.type = BTRFS_DIR_INDEX_KEY;
>         key.offset = 0;
> +
> +       odi = get_orphan_dir_info(sctx, dir);
> +       if (odi)
> +               key.offset = odi->last_dir_index_offset;
> +
>         ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
>         if (ret < 0)
>                 goto out;
> @@ -2968,30 +2976,33 @@ static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 dir_gen,
>
>                 dm = get_waiting_dir_move(sctx, loc.objectid);
>                 if (dm) {
> -                       struct orphan_dir_info *odi;
> -
>                         odi = add_orphan_dir_info(sctx, dir);
>                         if (IS_ERR(odi)) {
>                                 ret = PTR_ERR(odi);
>                                 goto out;
>                         }
>                         odi->gen = dir_gen;
> +                       odi->last_dir_index_offset = found_key.offset;
>                         dm->rmdir_ino = dir;
>                         ret = 0;
>                         goto out;
>                 }
>
>                 if (loc.objectid > send_progress) {
> -                       struct orphan_dir_info *odi;
> -
> -                       odi = get_orphan_dir_info(sctx, dir);
> -                       free_orphan_dir_info(sctx, odi);
> +                       odi = add_orphan_dir_info(sctx, dir);
> +                       if (IS_ERR(odi)) {
> +                               ret = PTR_ERR(odi);
> +                               goto out;
> +                       }
> +                       odi->gen = dir_gen;
> +                       odi->last_dir_index_offset = found_key.offset;
>                         ret = 0;
>                         goto out;
>                 }
>
>                 path->slots[0]++;
>         }
> +       free_orphan_dir_info(sctx, odi);
>
>         ret = 1;
>
> @@ -3269,13 +3280,16 @@ static int apply_dir_move(struct send_ctx *sctx, struct pending_dir_move *pm)
>
>         if (rmdir_ino) {
>                 struct orphan_dir_info *odi;
> +               u64 gen;
>
>                 odi = get_orphan_dir_info(sctx, rmdir_ino);
>                 if (!odi) {
>                         /* already deleted */
>                         goto finish;
>                 }
> -               ret = can_rmdir(sctx, rmdir_ino, odi->gen, sctx->cur_ino);
> +               gen = odi->gen;
> +
> +               ret = can_rmdir(sctx, rmdir_ino, gen, sctx->cur_ino);
>                 if (ret < 0)
>                         goto out;
>                 if (!ret)
> @@ -3286,13 +3300,12 @@ static int apply_dir_move(struct send_ctx *sctx, struct pending_dir_move *pm)
>                         ret = -ENOMEM;
>                         goto out;
>                 }
> -               ret = get_cur_path(sctx, rmdir_ino, odi->gen, name);
> +               ret = get_cur_path(sctx, rmdir_ino, gen, name);
>                 if (ret < 0)
>                         goto out;
>                 ret = send_rmdir(sctx, name);
>                 if (ret < 0)
>                         goto out;
> -               free_orphan_dir_info(sctx, odi);
>         }
>
>  finish:
> --
> 1.9.1
>
> --
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-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”