linux-kernel - Re: [PATCH 16/16] dm-zoned: ensure only power of 2 zone sizes are allowed

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Message-ID: <2ffc46c7-945f-ba26-90db-737fccd74fdf@opensource.wdc.com>
Date:   Thu, 28 Apr 2022 08:42:41 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Pankaj Raghav <p.raghav@...sung.com>, jaegeuk@...nel.org,
        axboe@...nel.dk, snitzer@...nel.org, hch@....de, mcgrof@...nel.org,
        naohiro.aota@....com, sagi@...mberg.me, dsterba@...e.com,
        johannes.thumshirn@....com
Cc:     linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
        clm@...com, gost.dev@...sung.com, chao@...nel.org,
        linux-f2fs-devel@...ts.sourceforge.net, josef@...icpanda.com,
        jonathan.derrick@...ux.dev, agk@...hat.com, kbusch@...nel.org,
        kch@...dia.com, linux-nvme@...ts.infradead.org,
        dm-devel@...hat.com, bvanassche@....org, jiangbo.365@...edance.com,
        linux-fsdevel@...r.kernel.org, matias.bjorling@....com,
        linux-block@...r.kernel.org
Subject: Re: [PATCH 16/16] dm-zoned: ensure only power of 2 zone sizes are
 allowed

On 4/28/22 01:02, Pankaj Raghav wrote:
> From: Luis Chamberlain <mcgrof@...nel.org>
> 
> Today dm-zoned relies on the assumption that you have a zone size
> with a power of 2. Even though the block layer today enforces this
> requirement, these devices do exist and so provide a stop-gap measure
> to ensure these devices cannot be used by mistake
> 
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
>  drivers/md/dm-zone.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/md/dm-zone.c b/drivers/md/dm-zone.c
> index 57daa86c19cf..221e0aa0f1a7 100644
> --- a/drivers/md/dm-zone.c
> +++ b/drivers/md/dm-zone.c
> @@ -231,6 +231,18 @@ static int dm_revalidate_zones(struct mapped_device *md, struct dm_table *t)
>  	struct request_queue *q = md->queue;
>  	unsigned int noio_flag;
>  	int ret;
> +	struct block_device *bdev = md->disk->part0;
> +	sector_t zone_sectors;
> +	char bname[BDEVNAME_SIZE];
> +
> +	zone_sectors = bdev_zone_sectors(bdev);
> +
> +	if (!is_power_of_2(zone_sectors)) {
> +		DMWARN("%s: %s only power of two zone size supported\n",
> +		       dm_device_name(md),
> +		       bdevname(bdev, bname));
> +		return 1;
> +	}

Why ?

See my previous email about still allowing ZC < ZS for non power of 2 zone
size drives. dm-zoned can easily support non power of 2 zone size as long
as ZC == ZS for all zones.

The problem with dm-zoned is ZC < ZS *AND* potentially variable ZC per
zone. That cannot be supported easily (still not impossible, but
definitely a lot more complex).

>  
>  	/*
>  	 * Check if something changed. If yes, cleanup the current resources


-- 
Damien Le Moal
Western Digital Research