linux-kernel - Re: [PATCH RFC v2 02/10] md/raid0: convert raid0_handle_discard() to use bio_submit_split

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Message-ID: <858e0210-1bbb-466b-98c3-d1a3c834519d@kernel.org>
Date: Sat, 30 Aug 2025 09:41:02 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Yu Kuai <yukuai1@...weicloud.com>, axboe@...nel.dk, tj@...nel.org,
 josef@...icpanda.com, song@...nel.org, neil@...wn.name,
 akpm@...ux-foundation.org, hch@...radead.org, colyli@...nel.org,
 hare@...e.de, tieren@...as.com
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, linux-raid@...r.kernel.org, yukuai3@...wei.com,
 yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com
Subject: Re: [PATCH RFC v2 02/10] md/raid0: convert raid0_handle_discard() to
 use bio_submit_split_bioset()

On 8/28/25 15:57, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> On the one hand unify bio split code, prepare to fix disordered split
> IO; On the other hand fix missing blkcg_bio_issue_init() and
> trace_block_split() for split IO.

Hmmm... Shouldn't that be a prep patch with a fixes tag for backport ?
Because that "fix" here is not done directly but is the result of calling
bio_submit_split_bioset().

> 
> Noted commit 319ff40a5427 ("md/raid0: Fix performance regression for large
> sequential writes") already fix disordered split IO by converting bio to
> underlying disks before submit_bio_noacct(), with the respect
> md_submit_bio() already split by sectors, and raid0_make_request() will
> split at most once for unaligned IO. This is a bit hacky and we'll convert
> this to solution in general later.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
>  drivers/md/raid0.c | 19 +++++++------------
>  1 file changed, 7 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index f1d8811a542a..4dcc5133d679 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -463,21 +463,16 @@ static void raid0_handle_discard(struct mddev *mddev, struct bio *bio)
>  	zone = find_zone(conf, &start);
>  
>  	if (bio_end_sector(bio) > zone->zone_end) {
> -		struct bio *split = bio_split(bio,
> -			zone->zone_end - bio->bi_iter.bi_sector, GFP_NOIO,
> -			&mddev->bio_set);
> -
> -		if (IS_ERR(split)) {
> -			bio->bi_status = errno_to_blk_status(PTR_ERR(split));
> -			bio_endio(bio);
> +		bio = bio_submit_split_bioset(bio,
> +				zone->zone_end - bio->bi_iter.bi_sector,

Can this ever be negative (of course not I think)? But if
bio_submit_split_bioset() is changed to have an unsigned int sectors count,
maybe add a sanity check before calling bio_submit_split_bioset() ?

> +				&mddev->bio_set);
> +		if (!bio)
>  			return;
> -		}
> -		bio_chain(split, bio);
> -		submit_bio_noacct(bio);
> -		bio = split;
> +
>  		end = zone->zone_end;
> -	} else
> +	} else {
>  		end = bio_end_sector(bio);
> +	}
>  
>  	orig_end = end;
>  	if (zone != conf->strip_zone)


-- 
Damien Le Moal
Western Digital Research