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: <e147e288-de38-4f2c-8068-53c5e37b2310@yukuai.org.cn>
Date: Sat, 30 Aug 2025 12:10:29 +0800
From: Yu Kuai <hailan@...uai.org.cn>
To: Damien Le Moal <dlemoal@...nel.org>, 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()

Hi,

在 2025/8/30 8:41, Damien Le Moal 写道:
> 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().

I can add a fix tag as blkcg_bio_issue_init() and trace_block_split() is missed,
however, if we consider stable backport, should we fix this directly from caller
first? As this is better for backport. Later this patch can be just considered
cleanup.

>> 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() ?

Yes, this can never be negative.

Thanks,
Kuai

>
>> +				&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)
>