linux-kernel - Re: [PATCH AUTOSEL 5.9 089/147] dm: change max_io_len() to use blk_max_size

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Date:   Tue, 27 Oct 2020 08:19:59 -0400
From:   Mike Snitzer <snitzer@...hat.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        dm-devel@...hat.com
Subject: Re: [PATCH AUTOSEL 5.9 089/147] dm: change max_io_len() to use
 blk_max_size_offset()

On Mon, Oct 26 2020 at  7:48pm -0400,
Sasha Levin <sashal@...nel.org> wrote:

> From: Mike Snitzer <snitzer@...hat.com>
> 
> [ Upstream commit 5091cdec56faeaefa79de4b6cb3c3c55e50d1ac3 ]
> 
> Using blk_max_size_offset() enables DM core's splitting to impose
> ti->max_io_len (via q->limits.chunk_sectors) and also fallback to
> respecting q->limits.max_sectors if chunk_sectors isn't set.
> 
> Signed-off-by: Mike Snitzer <snitzer@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

Not sure why this commit elevated to stable@ picking it up, please
explain.

But you cannot take this commit standalone. These commits are prereqs:

22ada802ede8 block: use lcm_not_zero() when stacking chunk_sectors
07d098e6bbad block: allow 'chunk_sectors' to be non-power-of-2
882ec4e609c1 dm table: stack 'chunk_sectors' limit to account for target-specific splitting

This goes for all stable@ trees you AUTOSEL'd commit 5091cdec56f for.

Mike

> ---
>  drivers/md/dm.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 6ed05ca65a0f8..3982012b1309c 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1051,22 +1051,18 @@ static sector_t max_io_len_target_boundary(sector_t sector, struct dm_target *ti
>  static sector_t max_io_len(sector_t sector, struct dm_target *ti)
>  {
>  	sector_t len = max_io_len_target_boundary(sector, ti);
> -	sector_t offset, max_len;
> +	sector_t max_len;
>  
>  	/*
>  	 * Does the target need to split even further?
> +	 * - q->limits.chunk_sectors reflects ti->max_io_len so
> +	 *   blk_max_size_offset() provides required splitting.
> +	 * - blk_max_size_offset() also respects q->limits.max_sectors
>  	 */
> -	if (ti->max_io_len) {
> -		offset = dm_target_offset(ti, sector);
> -		if (unlikely(ti->max_io_len & (ti->max_io_len - 1)))
> -			max_len = sector_div(offset, ti->max_io_len);
> -		else
> -			max_len = offset & (ti->max_io_len - 1);
> -		max_len = ti->max_io_len - max_len;
> -
> -		if (len > max_len)
> -			len = max_len;
> -	}
> +	max_len = blk_max_size_offset(dm_table_get_md(ti->table)->queue,
> +				      dm_target_offset(ti, sector));
> +	if (len > max_len)
> +		len = max_len;
>  
>  	return len;
>  }
> -- 
> 2.25.1
>