Re: [PATCH] md: support to align bio to limits

["Yu Kuai" <yukuai@fnnas.com>]

Hi,

I forgot to remove this patch, that is patch 3 in this set, before sending
to mail list, please ignore this one.

在 2025/11/21 13:14, Yu Kuai 写道:
> For personalities that report optimal IO size, it's indicate that users
> can get the best IO bandwidth if they issue IO with this size. However
> there is also an implicit condition that IO should also be aligned to the
> optimal IO size.
>
> Currently, bio will only be split by limits, if bio offset is not aligned
> to limits, then all split bio will not be aligned. This patch add a new
> feature to align bio to limits first, and following patches will support
> this for each personality if necessary.
>
> Signed-off-by: Yu Kuai <yukuai@fnnas.com>
> ---
>   drivers/md/md.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>   drivers/md/md.h |  1 +
>   2 files changed, 47 insertions(+)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 7b5c5967568f..b09f87b27807 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -427,6 +427,48 @@ bool md_handle_request(struct mddev *mddev, struct bio *bio)
>   }
>   EXPORT_SYMBOL(md_handle_request);
>   
> +static struct bio *__md_bio_align_to_limits(struct mddev *mddev,
> +					    struct bio *bio)
> +{
> +	unsigned int max_sectors = mddev->gendisk->queue->limits.max_sectors;
> +	sector_t start = bio->bi_iter.bi_sector;
> +	sector_t align_start = roundup(start, max_sectors);
> +	sector_t end;
> +	sector_t align_end;
> +
> +	/* already aligned */
> +	if (align_start == start)
> +		return bio;
> +
> +	end = start + bio_sectors(bio);
> +	align_end = rounddown(end, max_sectors);
> +
> +	/* bio is too small to split */
> +	if (align_end <= align_start)
> +		return bio;
> +
> +	return bio_submit_split_bioset(bio, align_start - start,
> +				       &mddev->gendisk->bio_split);
> +}
> +
> +static struct bio *md_bio_align_to_limits(struct mddev *mddev, struct bio *bio)
> +{
> +	if (!mddev->bio_align_to_limits)
> +		return bio;
> +
> +	/* atomic write can't split */
> +	if (bio->bi_opf & REQ_ATOMIC)
> +		return bio;
> +
> +	switch (bio_op(bio)) {
> +	case REQ_OP_READ:
> +	case REQ_OP_WRITE:
> +		return __md_bio_align_to_limits(mddev, bio);
> +	default:
> +		return bio;
> +	}
> +}
> +
>   static void md_submit_bio(struct bio *bio)
>   {
>   	const int rw = bio_data_dir(bio);
> @@ -442,6 +484,10 @@ static void md_submit_bio(struct bio *bio)
>   		return;
>   	}
>   
> +	bio = md_bio_align_to_limits(mddev, bio);
> +	if (!bio)
> +		return;
> +
>   	bio = bio_split_to_limits(bio);
>   	if (!bio)
>   		return;
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index 75fd8c873b6f..1ed90fd85ac4 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -630,6 +630,7 @@ struct mddev {
>   	bool	has_superblocks:1;
>   	bool	fail_last_dev:1;
>   	bool	serialize_policy:1;
> +	bool	bio_align_to_limits:1;
>   };
>   
>   enum recovery_flags {

-- 
Thanks,
Kuai