linux-kernel - Re: [PATCH RFC md-6.16 v3 02/19] md: support discard for bitmap ops

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Message-ID: <2830c5d0-cc04-51eb-6785-79d0a43f4fc4@huaweicloud.com>
Date: Mon, 12 May 2025 14:05:56 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Christoph Hellwig <hch@....de>, Yu Kuai <yukuai1@...weicloud.com>
Cc: xni@...hat.com, colyli@...nel.org, agk@...hat.com, snitzer@...nel.org,
 mpatocka@...hat.com, song@...nel.org, linux-kernel@...r.kernel.org,
 dm-devel@...ts.linux.dev, linux-raid@...r.kernel.org, yi.zhang@...wei.com,
 yangerkun@...wei.com, johnny.chenyi@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC md-6.16 v3 02/19] md: support discard for bitmap ops

Hi,

在 2025/05/12 12:41, Christoph Hellwig 写道:
> On Mon, May 12, 2025 at 09:19:10AM +0800, Yu Kuai wrote:
>> +++ b/drivers/md/md.c
>> @@ -8849,14 +8849,24 @@ static void md_bitmap_start(struct mddev *mddev,
>>   		mddev->pers->bitmap_sector(mddev, &md_io_clone->offset,
>>   					   &md_io_clone->sectors);
>>   
>> -	mddev->bitmap_ops->startwrite(mddev, md_io_clone->offset,
>> -				      md_io_clone->sectors);
>> +	if (unlikely(md_io_clone->rw == STAT_DISCARD) &&
>> +	    mddev->bitmap_ops->start_discard)
>> +		mddev->bitmap_ops->start_discard(mddev, md_io_clone->offset,
>> +						 md_io_clone->sectors);
>> +	else
>> +		mddev->bitmap_ops->startwrite(mddev, md_io_clone->offset,
>> +					      md_io_clone->sectors);
>>   }
> 
> This interface feels weird, as it would still call into the write
> interfaces when the discard ones are not defined instead of doing
> nothing.  Also shouldn't discard also use a different interface
> than md_bitmap_start in the caller?

This is because the old bitmap handle discard the same as write, I
can't do nothing in this case. Do you prefer also reuse the write
api to new discard api for old bitmap?

For the caller, I think it's fine, since bitmap framwork already
calculate sectors and len for discard as well.
> 
> I'd also expect the final version of this to be merged with the
> previous patch, as adding an interface without the only user is a
> bit odd.

Sure.

Thanks,
Kuai

> .
>