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Message-ID: <2c275ab0-c813-22ae-16e3-b16885d06c4c@opensource.wdc.com>
Date:   Wed, 4 May 2022 01:43:19 +0900
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Subject: Re: [PATCH 01/16] block: make blkdev_nr_zones and blk_queue_zone_no
 generic for npo2 zsze
Content-Language: en-US
To:     Bart Van Assche <bvanassche@acm.org>,
        Pankaj Raghav <p.raghav@samsung.com>, jaegeuk@kernel.org,
        axboe@kernel.dk, snitzer@kernel.org, hch@lst.de, mcgrof@kernel.org,
        naohiro.aota@wdc.com, sagi@grimberg.me, dsterba@suse.com,
        johannes.thumshirn@wdc.com
Cc:     linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org,
        clm@fb.com, gost.dev@samsung.com, chao@kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, josef@toxicpanda.com,
        jonathan.derrick@linux.dev, agk@redhat.com, kbusch@kernel.org,
        kch@nvidia.com, linux-nvme@lists.infradead.org,
        dm-devel@redhat.com, jiangbo.365@bytedance.com,
        linux-fsdevel@vger.kernel.org, matias.bjorling@wdc.com,
        linux-block@vger.kernel.org
References: <20220427160255.300418-1-p.raghav@samsung.com>
 <CGME20220427160257eucas1p21fb58d0129376a135fdf0b9c2fe88895@eucas1p2.samsung.com>
 <20220427160255.300418-2-p.raghav@samsung.com>
 <3a178153-62c0-e298-ccb0-0edfd41b7ee2@acm.org>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <3a178153-62c0-e298-ccb0-0edfd41b7ee2@acm.org>
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Precedence: bulk

On 2022/05/04 1:37, Bart Van Assche wrote:
> On 4/27/22 09:02, Pankaj Raghav wrote:
>> Adapt blkdev_nr_zones and blk_queue_zone_no function so that it can
>> also work for non-power-of-2 zone sizes.
>>
>> As the existing deployments of zoned devices had power-of-2
>> assumption, power-of-2 optimized calculation is kept for those devices.
>>
>> There are no direct hot paths modified and the changes just
>> introduce one new branch per call.
>>
>> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
>> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
>> ---
>>   block/blk-zoned.c      | 8 +++++++-
>>   include/linux/blkdev.h | 8 +++++++-
>>   2 files changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
>> index 38cd840d8838..1dff4a8bd51d 100644
>> --- a/block/blk-zoned.c
>> +++ b/block/blk-zoned.c
>> @@ -117,10 +117,16 @@ EXPORT_SYMBOL_GPL(__blk_req_zone_write_unlock);
>>   unsigned int blkdev_nr_zones(struct gendisk *disk)
>>   {
>>   	sector_t zone_sectors = blk_queue_zone_sectors(disk->queue);
>> +	sector_t capacity = get_capacity(disk);
>>   
>>   	if (!blk_queue_is_zoned(disk->queue))
>>   		return 0;
>> -	return (get_capacity(disk) + zone_sectors - 1) >> ilog2(zone_sectors);
>> +
>> +	if (is_power_of_2(zone_sectors))
>> +		return (capacity + zone_sectors - 1) >>
>> +		       ilog2(zone_sectors);
>> +
>> +	return div64_u64(capacity + zone_sectors - 1, zone_sectors);
>>   }
>>   EXPORT_SYMBOL_GPL(blkdev_nr_zones);
> 
> Does anyone need support for more than 4 billion sectors per zone? If 
> not, do_div() should be sufficient.
> 
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index 60d016138997..c4e4c7071b7b 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -665,9 +665,15 @@ static inline unsigned int blk_queue_nr_zones(struct request_queue *q)
>>   static inline unsigned int blk_queue_zone_no(struct request_queue *q,
>>   					     sector_t sector)
>>   {
>> +	sector_t zone_sectors = blk_queue_zone_sectors(q);
>> +
>>   	if (!blk_queue_is_zoned(q))
>>   		return 0;
>> -	return sector >> ilog2(q->limits.chunk_sectors);
>> +
>> +	if (is_power_of_2(zone_sectors))
>> +		return sector >> ilog2(zone_sectors);
>> +
>> +	return div64_u64(sector, zone_sectors);
>>   }
> 
> Same comment here.

sector_t is 64-bits even on 32-bits arch, no ?
so div64_u64 is needed here I think, which will be a simple regular division for
64-bit arch.

> 
> Thanks,
> 
> Bart.


-- 
Damien Le Moal
Western Digital Research