Re: [PATCH 1/2] btrfs: consume the given iter directly instead of copying in csum_one_bio()

[Daniel Vacek]

On Wed, 2 Sept 2026 at 18:51, Daniel Vacek <neelx@xxxxxxxx> wrote:
> This is just a small cleanup to avoid copying the iter twice in async case.
> We already have a copy csum_one_bio() can consume directly. No need to copy
> again the second time.
> In the sync case we can copy in the caller (as we did before dd57c78aec39
> ("btrfs: introduce btrfs_bio::async_csum")).
>
> Signed-off-by: Daniel Vacek <neelx@xxxxxxxx>
> ---
>  fs/btrfs/file-item.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
> index 581ca5653be9..5a5cffb18922 100644
> --- a/fs/btrfs/file-item.c
> +++ b/fs/btrfs/file-item.c
> @@ -797,18 +797,16 @@ int btrfs_lookup_csums_bitmap(struct btrfs_root *root, struct btrfs_path *path,
>         return ret;
>  }
>
> -static void csum_one_bio(struct btrfs_bio *bbio, struct bvec_iter *src)
> +static void csum_one_bio(struct btrfs_bio *bbio, struct bvec_iter *iter)
>  {
>         struct btrfs_inode *inode = bbio->inode;
>         struct btrfs_fs_info *fs_info = inode->root->fs_info;
>         struct btrfs_ordered_sum *sums = bbio->sums;
> -       struct bvec_iter iter;
>         const u32 blocksize = fs_info->sectorsize;
>         int index = 0;
>
> -       for (iter = *src; iter.bi_size; bio_advance_iter(&bbio->bio, &iter, blocksize)) {
> -               btrfs_csum_one_bio_block(fs_info, &bbio->bio, &iter,
> -                                        sums->sums + index);
> +       for (; iter->bi_size; bio_advance_iter(&bbio->bio, iter, blocksize)) {
> +               btrfs_csum_one_bio_block(fs_info, &bbio->bio, iter, sums->sums + index);
>
>                 index += fs_info->csum_size;
>         }
> @@ -851,12 +849,14 @@ int btrfs_csum_one_bio(struct btrfs_bio *bbio, bool async)
>         btrfs_add_ordered_sum(ordered, sums);
>
>         if (!async) {
> -               csum_one_bio(bbio, &bbio->bio.bi_iter);
> +               struct bvec_iter iter = bio->bi_iter;
> +
> +               csum_one_bio(bbio, &iter);
>                 return 0;
>         }
>         init_completion(&bbio->csum_done);
>         bbio->async_csum = true;
> -       bbio->csum_saved_iter = bbio->bio.bi_iter;
> +       bbio->csum_saved_iter = bio->bi_iter;

Actually we can use this one unconditionally in both cases and save
the stack space.

And unifying both cases will allow us getting rid of the paramert.

I'll send a v2 shortly.

--nX

>         INIT_WORK(&bbio->csum_work, csum_one_bio_work);
>         schedule_work(&bbio->csum_work);
>         return 0;
> --
> 2.53.0
>