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Message-ID: <501aba4d-f4a3-8a4d-ec2a-99c7319b6a4d@opensource.wdc.com>
Date:   Mon, 16 May 2022 16:02:18 +0200
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Subject: Re: [dm-devel] [PATCH v4 03/13] nvme: zns: Allow ZNS drives that have
 non-power_of_2 zone size
Content-Language: en-US
To:     Pankaj Raghav <p.raghav@samsung.com>, axboe@kernel.dk,
        naohiro.aota@wdc.com, Johannes.Thumshirn@wdc.com,
        snitzer@kernel.org, dsterba@suse.com, jaegeuk@kernel.org,
        hch@lst.de
Cc:     jiangbo.365@bytedance.com, Jens Axboe <axboe@fb.com>,
        Chaitanya Kulkarni <kch@nvidia.com>, bvanassche@acm.org,
        Chris Mason <clm@fb.com>, matias.bjorling@wdc.com,
        gost.dev@samsung.com, Luis Chamberlain <mcgrof@kernel.org>,
        linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        Josef Bacik <josef@toxicpanda.com>,
        linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        dm-devel@redhat.com, Alasdair Kergon <agk@redhat.com>,
        jonathan.derrick@linux.dev, Keith Busch <kbusch@kernel.org>,
        Johannes Thumshirn <jth@kernel.org>,
        linux-btrfs@vger.kernel.org, Sagi Grimberg <sagi@grimberg.me>
References: <20220516133921.126925-1-p.raghav@samsung.com>
 <CGME20220516133926eucas1p15c7ba425b67ce4ac824c6bd3263e2dd4@eucas1p1.samsung.com>
 <20220516133921.126925-4-p.raghav@samsung.com>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <20220516133921.126925-4-p.raghav@samsung.com>
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Precedence: bulk

On 2022/05/16 15:39, Pankaj Raghav wrote:
> Remove the condition which disallows non-power_of_2 zone size ZNS drive
> to be updated and use generic method to calculate number of zones
> instead of relying on log and shift based calculation on zone size.
> 
> The power_of_2 calculation has been replaced directly with generic
> calculation without special handling. Both modified functions are not
> used in hot paths, they are only used during initialization &
> revalidation of the ZNS device.
> 
> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
> Reviewed by: Adam Manzanares <a.manzanares@samsung.com>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>  drivers/nvme/host/zns.c | 24 +++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/nvme/host/zns.c b/drivers/nvme/host/zns.c
> index 9f81beb4d..65d2aa68a 100644
> --- a/drivers/nvme/host/zns.c
> +++ b/drivers/nvme/host/zns.c
> @@ -101,13 +101,6 @@ int nvme_update_zone_info(struct nvme_ns *ns, unsigned lbaf)
>  	}
>  
>  	ns->zsze = nvme_lba_to_sect(ns, le64_to_cpu(id->lbafe[lbaf].zsze));
> -	if (!is_power_of_2(ns->zsze)) {
> -		dev_warn(ns->ctrl->device,
> -			"invalid zone size:%llu for namespace:%u\n",
> -			ns->zsze, ns->head->ns_id);
> -		status = -ENODEV;
> -		goto free_data;
> -	}
>  
>  	blk_queue_set_zoned(ns->disk, BLK_ZONED_HM);
>  	blk_queue_flag_set(QUEUE_FLAG_ZONE_RESETALL, q);
> @@ -128,8 +121,13 @@ static void *nvme_zns_alloc_report_buffer(struct nvme_ns *ns,
>  	const size_t min_bufsize = sizeof(struct nvme_zone_report) +
>  				   sizeof(struct nvme_zone_descriptor);
>  
> +	/*
> +	 * Division is used to calculate nr_zones with no special handling
> +	 * for power of 2 zone sizes as this function is not invoked in a
> +	 * hot path
> +	 */

Comment not very useful.

>  	nr_zones = min_t(unsigned int, nr_zones,
> -			 get_capacity(ns->disk) >> ilog2(ns->zsze));
> +			 div64_u64(get_capacity(ns->disk), ns->zsze));
>  
>  	bufsize = sizeof(struct nvme_zone_report) +
>  		nr_zones * sizeof(struct nvme_zone_descriptor);
> @@ -182,6 +180,7 @@ int nvme_ns_report_zones(struct nvme_ns *ns, sector_t sector,
>  	int ret, zone_idx = 0;
>  	unsigned int nz, i;
>  	size_t buflen;
> +	u64 remainder = 0;
>  
>  	if (ns->head->ids.csi != NVME_CSI_ZNS)
>  		return -EINVAL;
> @@ -197,7 +196,14 @@ int nvme_ns_report_zones(struct nvme_ns *ns, sector_t sector,
>  	c.zmr.zrasf = NVME_ZRASF_ZONE_REPORT_ALL;
>  	c.zmr.pr = NVME_REPORT_ZONE_PARTIAL;
>  
> -	sector &= ~(ns->zsze - 1);
> +	/*
> +	 * rounddown the sector value to the nearest zone size. roundown macro
> +	 * provided in math.h will not work for 32 bit architectures.
> +	 * Division is used here with no special handling for power of 2
> +	 * zone sizes as this function is not invoked in a hot path
> +	 */

Please simplify this to:

	/* Round down the sector value to the nearest zone start */

> +	div64_u64_rem(sector, ns->zsze, &remainder);
> +	sector -= remainder;
>  	while (zone_idx < nr_zones && sector < get_capacity(ns->disk)) {
>  		memset(report, 0, buflen);
>  


-- 
Damien Le Moal
Western Digital Research