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

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Message-ID: <20250512044125.GB868@lst.de>
Date: Mon, 12 May 2025 06:41:25 +0200
From: Christoph Hellwig <hch@....de>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: hch@....de, xni@...hat.com, colyli@...nel.org, agk@...hat.com,
	snitzer@...nel.org, mpatocka@...hat.com, song@...nel.org,
	yukuai3@...wei.com, 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
Subject: Re: [PATCH RFC md-6.16 v3 02/19] md: support discard for bitmap ops

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?

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.