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Date:   Tue, 6 Dec 2022 00:45:12 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Qu Wenruo <wqu@suse.com>
Cc:     linux-btrfs@vger.kernel.org
Subject: Re: [PoC PATCH 05/11] btrfs: scrub: add a writeback helper for
 scrub2_stripe
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References: <cover.1670314744.git.wqu@suse.com>
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> +static void scrub2_write_endio(struct btrfs_bio *bbio)
> +{
> +	struct scrub2_stripe *stripe = bbio->private;
> +	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
> +	struct bio_vec *first_bvec = bio_first_bvec_all(&bbio->bio);
> +	struct bio_vec *bvec;
> +	struct bvec_iter_all iter_all;
> +	unsigned long flags;
> +	int bio_size = 0;
> +	int first_sector_nr;
> +	int i;
> +
> +	bio_for_each_segment_all(bvec, &bbio->bio, iter_all)
> +		bio_size += bvec->bv_len;

If you use bio_for_each_bvec_all instead the loop will be significantly
cheaper.