linux-kernel - Re: [PATCH v8 02/11] block: allow blk-zoned devices to have non-power-of-2 zone size

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Message-ID: <9eed99b8-7e35-841c-5ec1-97b7107f328f@samsung.com>
Date:   Thu, 28 Jul 2022 14:24:56 +0200
From:   Pankaj Raghav <p.raghav@...sung.com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>, <hch@....de>,
        <axboe@...nel.dk>, <snitzer@...nel.org>,
        <Johannes.Thumshirn@....com>
CC:     <matias.bjorling@....com>, <gost.dev@...sung.com>,
        <linux-kernel@...r.kernel.org>, <hare@...e.de>,
        <linux-block@...r.kernel.org>, <pankydev8@...il.com>,
        <bvanassche@....org>, <jaegeuk@...nel.org>, <dm-devel@...hat.com>,
        <linux-nvme@...ts.infradead.org>,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [PATCH v8 02/11] block: allow blk-zoned devices to have
 non-power-of-2 zone size

On 2022-07-28 05:07, Damien Le Moal wrote:
> On 7/28/22 01:22, Pankaj Raghav wrote:
>> Checking if a given sector is aligned to a zone is a common
>> operation that is performed for zoned devices. Add
>> bdev_is_zone_start helper to check for this instead of opencoding it
> 
> The patch actually introduces bdev_is_zone_aligned(). I agree with Bart
> that bdev_is_zone_start() is a better name.
I have posted my rationale behind this change in my reply to Bart. Let
me know what you think.
>

<snip>
>>  		args->zone_sectors = zone->len;
>> -		args->nr_zones = (capacity + zone->len - 1) >> ilog2(zone->len);
>> +		args->nr_zones = div64_u64(capacity + zone->len - 1, zone->len);
> 
> 		args->nr_zones = disk_zone_no(disk, capacity);
> 
We are doing a round up with a division here mainly to take into account
the last unequal zone if present. disk_zone_no does just a division so
it won't account for the unequal last zone.

>>  	} else if (zone->start + args->zone_sectors < capacity) {
>>  		if (zone->len != args->zone_sectors) {
>>  			pr_warn("%s: Invalid zoned device with non constant zone size\n",
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index 85b832908f28..1be805223026 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -634,6 +634,11 @@ static inline bool queue_is_mq(struct request_queue *q)
>>  	return q->mq_ops;
>>  }
>>  
>> +static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
>> +{
>> +	return bdev->bd_queue;	/* this is never NULL */
>> +}
>> +
>>  #ifdef CONFIG_PM
>>  static inline enum rpm_status queue_rpm_status(struct request_queue *q)
>>  {
>> @@ -665,6 +670,25 @@ static inline bool blk_queue_is_zoned(struct request_queue *q)
>>  	}
>>  }
>>  
>> +static inline bool bdev_is_zoned(struct block_device *bdev)
>> +{
>> +	struct request_queue *q = bdev_get_queue(bdev);
>> +
>> +	if (q)
>> +		return blk_queue_is_zoned(q);
>> +
>> +	return false;
>> +}
>> +
>> +static inline sector_t bdev_zone_sectors(struct block_device *bdev)
>> +{
>> +	struct request_queue *q = bdev_get_queue(bdev);
>> +
>> +	if (!blk_queue_is_zoned(q))
>> +		return 0;
>> +	return q->limits.chunk_sectors;
>> +}
>> +
>>  #ifdef CONFIG_BLK_DEV_ZONED
>>  static inline unsigned int disk_nr_zones(struct gendisk *disk)
>>  {
>> @@ -684,6 +708,30 @@ static inline unsigned int disk_zone_no(struct gendisk *disk, sector_t sector)
>>  	return div64_u64(sector, zone_sectors);
>>  }
>>  
>> +static inline sector_t bdev_offset_from_zone_start(struct block_device *bdev,
>> +						   sector_t sec)
>> +{
>> +	sector_t zone_sectors = bdev_zone_sectors(bdev);
>> +	u64 remainder = 0;
>> +
>> +	if (!bdev_is_zoned(bdev))
>> +		return 0;
>> +
>> +	if (is_power_of_2(zone_sectors))
>> +		return sec & (zone_sectors - 1);
>> +
>> +	div64_u64_rem(sec, zone_sectors, &remainder);
>> +	return remainder;
>> +}
>> +
>> +static inline bool bdev_is_zone_aligned(struct block_device *bdev, sector_t sec)
>> +{
>> +	if (!bdev_is_zoned(bdev))
>> +		return false;
> 
> This is checked in bdev_offset_from_zone_start(). No need to add it again
> here.
> 
bdev_offset_from_zone_start returns 0 if the device is not zoned, and
the below check will then return `true`. That is why I explicitly return
a false if the device is not zoned.
>> +
>> +	return bdev_offset_from_zone_start(bdev, sec) == 0;
>> +}
>> +
>>  static inline bool disk_zone_is_seq(struct gendisk *disk, sector_t sector)
>>  {
>>  	if (!blk_queue_is_zoned(disk->queue))
>> @@ -728,6 +776,18 @@ static inline unsigned int disk_zone_no(struct gendisk *disk, sector_t sector)
>>  {
>>  	return 0;
>>  }
>> +
>> +static inline sector_t bdev_offset_from_zone_start(struct block_device *bdev,
>> +						   sector_t sec)
>> +{
>> +	return 0;
>> +}
> 
> This one is not used when CONFIG_BLK_DEV_ZONED is not set. No need to
> define it.
> 
Ok. I will remove it if it is not required.
>> +
>> +static inline bool bdev_is_zone_aligned(struct block_device *bdev, sector_t sec)
>> +{

>