Re: [PATCH RFC v2 08/10] block: skip unnecessary checks for split bio

[Damien Le Moal]

On 8/28/25 15:57, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
> 
> Lots of checks are already done while submitting this bio the first
> time, and there is no need to check them again when this bio is
> resubmitted after split.
> 
> Hence factor out a helper submit_split_bio_noacct() for resubmitting
> bio after splitting, only should_fail_bio() and blk_throtl_bio() are
> keeped.

s/keeped/kept

> 
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
>  block/blk-core.c  | 15 +++++++++++++++
>  block/blk-merge.c |  2 +-
>  block/blk.h       |  1 +
>  3 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 4201504158a1..37836446f365 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -765,6 +765,21 @@ static blk_status_t blk_validate_atomic_write_op_size(struct request_queue *q,
>  	return BLK_STS_OK;
>  }
>  
> +void submit_split_bio_noacct(struct bio *bio)
> +{
> +	might_sleep();
> +
> +	if (should_fail_bio(bio)) {
> +		bio_io_error(bio);
> +		return;
> +	}
> +
> +	if (blk_throtl_bio(bio))
> +		return;
> +
> +	submit_bio_noacct_nocheck(bio);
> +}
> +
>  /**
>   * submit_bio_noacct - re-submit a bio to the block device layer for I/O
>   * @bio:  The bio describing the location in memory and on the device.
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 3d6dc9cc4f61..fa2c3d98b277 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -131,7 +131,7 @@ struct bio *bio_submit_split_bioset(struct bio *bio, int split_sectors,
>  	bio_chain(split, bio);
>  	trace_block_split(split, bio->bi_iter.bi_sector);
>  	WARN_ON_ONCE(bio_zone_write_plugging(bio));
> -	submit_bio_noacct(bio);
> +	submit_split_bio_noacct(bio);

If this helper is used only here, I would just open-code it here as otherwise it
is confusing: its name has "split" in it but nothing of its code checks that the
BIO was actually split.

>  
>  	return split;
>  }
> diff --git a/block/blk.h b/block/blk.h
> index 46f566f9b126..80375374ef55 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -54,6 +54,7 @@ bool blk_queue_start_drain(struct request_queue *q);
>  bool __blk_freeze_queue_start(struct request_queue *q,
>  			      struct task_struct *owner);
>  int __bio_queue_enter(struct request_queue *q, struct bio *bio);
> +void submit_split_bio_noacct(struct bio *bio);
>  void submit_bio_noacct_nocheck(struct bio *bio);
>  void bio_await_chain(struct bio *bio);
>  


-- 
Damien Le Moal
Western Digital Research