linux-kernel - Re: [PATCH] btrfs: simplify async csum synchronization

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Message-ID: <6a7a088c-4e6f-4787-8513-bbe20658edcb@gmx.com>
Date: Thu, 13 Nov 2025 20:14:24 +1030
From: Qu Wenruo <quwenruo.btrfs@....com>
To: Daniel Vacek <neelx@...e.com>, Chris Mason <clm@...com>,
 Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>
Cc: Qu Wenruo <wqu@...e.com>, linux-btrfs@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: simplify async csum synchronization



在 2025/11/13 20:01, Daniel Vacek 写道:
> We don't need the completion csum_done which marks the csum work
> has been executed. We can simply flush_work() instead.
> 
> This way we can slim down the btrfs_bio structure by 32 bytes matching
> it's size to what it used to be before introducing the async csums.
> Hence not making any change with respect to the structure size.
> ---
> This is a simple fixup for "btrfs: introduce btrfs_bio::async_csum" in
> for-next and can be squashed into it.
> ---
>   fs/btrfs/bio.c       | 2 +-
>   fs/btrfs/bio.h       | 1 -
>   fs/btrfs/file-item.c | 6 +++---
>   3 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
> index a73652b8724a..fd6e4278a62f 100644
> --- a/fs/btrfs/bio.c
> +++ b/fs/btrfs/bio.c
> @@ -106,7 +106,7 @@ void btrfs_bio_end_io(struct btrfs_bio *bbio, blk_status_t status)
>   	ASSERT(in_task());
>   
>   	if (bbio->async_csum)
> -		wait_for_completion(&bbio->csum_done);
> +		flush_work(&bbio->csum_work);
>   
>   	bbio->bio.bi_status = status;
>   	if (bbio->bio.bi_pool == &btrfs_clone_bioset) {
> diff --git a/fs/btrfs/bio.h b/fs/btrfs/bio.h
> index deaeea3becf4..0b09d9122fa2 100644
> --- a/fs/btrfs/bio.h
> +++ b/fs/btrfs/bio.h
> @@ -57,7 +57,6 @@ struct btrfs_bio {
>   			struct btrfs_ordered_extent *ordered;
>   			struct btrfs_ordered_sum *sums;
>   			struct work_struct csum_work;
> -			struct completion csum_done;
>   			struct bvec_iter csum_saved_iter;
>   			u64 orig_physical;
>   		};
> diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
> index 72be3ede0edf..3e9241f360c8 100644
> --- a/fs/btrfs/file-item.c
> +++ b/fs/btrfs/file-item.c
> @@ -792,7 +792,6 @@ static void csum_one_bio_work(struct work_struct *work)
>   	ASSERT(btrfs_op(&bbio->bio) == BTRFS_MAP_WRITE);
>   	ASSERT(bbio->async_csum == true);
>   	csum_one_bio(bbio, &bbio->csum_saved_iter);
> -	complete(&bbio->csum_done);
>   }
>   
>   /*
> @@ -805,6 +804,7 @@ int btrfs_csum_one_bio(struct btrfs_bio *bbio, bool async)
>   	struct btrfs_fs_info *fs_info = inode->root->fs_info;
>   	struct bio *bio = &bbio->bio;
>   	struct btrfs_ordered_sum *sums;
> +	struct workqueue_struct *wq;
>   	unsigned nofs_flag;
>   
>   	nofs_flag = memalloc_nofs_save();
> @@ -825,11 +825,11 @@ int btrfs_csum_one_bio(struct btrfs_bio *bbio, bool async)
>   		csum_one_bio(bbio, &bbio->bio.bi_iter);
>   		return 0;
>   	}
> -	init_completion(&bbio->csum_done);
>   	bbio->async_csum = true;
>   	bbio->csum_saved_iter = bbio->bio.bi_iter;
>   	INIT_WORK(&bbio->csum_work, csum_one_bio_work);
> -	schedule_work(&bbio->csum_work);
> +	wq = bio->bi_opf & REQ_META? fs_info->endio_meta_workers: fs_info->endio_workers;

Metadata will not go into btrfs_csum_one_bio(), thus it's fixed to 
endio_workers().


> +	queue_work(wq, &bbio->csum_work);
>   	return 0;
>   }
>