linux-kernel - Re: [RFC PATCH v2 4/8] dm: add BLK_FEAT_WRITE_ZEROES

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Message-ID: <Z6aFtJzGWMNhILJW@redhat.com>
Date: Fri, 7 Feb 2025 17:14:12 -0500
From: Benjamin Marzinski <bmarzins@...hat.com>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-block@...r.kernel.org, dm-devel@...ts.linux.dev,
        linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, hch@....de, tytso@....edu,
        djwong@...nel.org, yi.zhang@...wei.com, chengzhihao1@...wei.com,
        yukuai3@...wei.com, yangerkun@...wei.com
Subject: Re: [RFC PATCH v2 4/8] dm: add BLK_FEAT_WRITE_ZEROES_UNMAP support

On Wed, Jan 15, 2025 at 07:46:33PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> Set the BLK_FEAT_WRITE_ZEROES_UNMAP feature on stacking queue limits by
> default. This feature shall be disabled if any underlying device does
> not support it.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> ---
>  drivers/md/dm-table.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index bd8b796ae683..58cce31bcc1e 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -598,7 +598,8 @@ int dm_split_args(int *argc, char ***argvp, char *input)
>  static void dm_set_stacking_limits(struct queue_limits *limits)
>  {
>  	blk_set_stacking_limits(limits);
> -	limits->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL;
> +	limits->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL |
> +			    BLK_FEAT_WRITE_ZEROES_UNMAP;
>  }
>  

dm_table_set_restrictions() can set limits->max_write_zeroes_sectors to
0, and it's called after dm_calculate_queue_limits(), which calls
blk_stack_limits(). Just to avoid having the BLK_FEAT_WRITE_ZEROES_UNMAP
still set while a device's max_write_zeroes_sectors is 0, it seems like
you would want to clear it as well if dm_table_set_restrictions() sets
limits->max_write_zeroes_sectors to 0.

-Ben

>  /*
> -- 
> 2.39.2
>