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

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Message-ID: <20250512061239.GA2893@lst.de>
Date: Mon, 12 May 2025 08:12:39 +0200
From: Christoph Hellwig <hch@....de>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: Christoph Hellwig <hch@....de>, 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

On Mon, May 12, 2025 at 02:05:56PM +0800, Yu Kuai wrote:
>>>   -	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?

It can just point the discard method to the same function as the
existing write one.