Re: [dm-devel] [PATCH v12 03/13] block: allow blk-zoned devices to have non-power-of-2 zone size

[Jonathan Derrick <jonathan.derrick@linux.dev>]

On 8/26/2022 2:06 PM, Jonathan Derrick wrote:
> 
> 
> On 8/23/2022 6:18 AM, 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
>> everywhere.
>>
>> Convert the calculations on zone size to be generic instead of relying on
>> power-of-2(po2) based arithmetic in the block layer using the helpers
>> wherever possible.
>>
>> The only hot path affected by this change for zoned devices with po2
>> zone size is in blk_check_zone_append() but bdev_is_zone_start() 
>> helper is
>> used to optimize the calculation for po2 zone sizes.
>>
>> Finally, allow zoned devices with non po2 zone sizes provided that their
>> zone capacity and zone size are equal. The main motivation to allow zoned
>> devices with non po2 zone size is to remove the unmapped LBA between
>> zone capcity and zone size for devices that cannot have a po2 zone
>> capacity.
>>
>> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
>> Reviewed-by: Hannes Reinecke <hare@suse.de>
>> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
>> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
>> ---
>>   block/blk-core.c       |  2 +-
>>   block/blk-zoned.c      | 24 ++++++++++++++++++------
>>   include/linux/blkdev.h | 30 ++++++++++++++++++++++++++++++
>>   3 files changed, 49 insertions(+), 7 deletions(-)
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index a0d1104c5590..1cb519220ffb 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -563,7 +563,7 @@ static inline blk_status_t 
>> blk_check_zone_append(struct request_queue *q,
>>           return BLK_STS_NOTSUPP;
>>       /* The bio sector must point to the start of a sequential zone */
>> -    if (bio->bi_iter.bi_sector & (bdev_zone_sectors(bio->bi_bdev) - 
>> 1) ||
>> +    if (!bdev_is_zone_start(bio->bi_bdev, bio->bi_iter.bi_sector) ||
>>           !bio_zone_is_seq(bio))
>>           return BLK_STS_IOERR;
>> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
>> index dce9c95b4bcd..6806c69c81dc 100644
>> --- a/block/blk-zoned.c
>> +++ b/block/blk-zoned.c
>> @@ -285,10 +285,10 @@ int blkdev_zone_mgmt(struct block_device *bdev, 
>> enum req_op op,
>>           return -EINVAL;
>>       /* Check alignment (handle eventual smaller last zone) */
>> -    if (sector & (zone_sectors - 1))
>> +    if (!bdev_is_zone_start(bdev, sector))
>>           return -EINVAL;
>> -    if ((nr_sectors & (zone_sectors - 1)) && end_sector != capacity)
>> +    if (!bdev_is_zone_start(bdev, nr_sectors) && end_sector != capacity)
>>           return -EINVAL;
>>       /*
>> @@ -486,14 +486,26 @@ static int blk_revalidate_zone_cb(struct 
>> blk_zone *zone, unsigned int idx,
>>        * smaller last zone.
>>        */
>>       if (zone->start == 0) {
>> -        if (zone->len == 0 || !is_power_of_2(zone->len)) {
>> -            pr_warn("%s: Invalid zoned device with non power of two 
>> zone size (%llu)\n",
>> -                disk->disk_name, zone->len);
>> +        if (zone->len == 0) {
>> +            pr_warn("%s: Invalid zero zone size", disk->disk_name);
>> +            return -ENODEV;
>> +        }
>> +
>> +        /*
>> +         * Non power-of-2 zone size support was added to remove the
>> +         * gap between zone capacity and zone size. Though it is 
>> technically
>> +         * possible to have gaps in a non power-of-2 device, Linux 
>> requires
>> +         * the zone size to be equal to zone capacity for non power-of-2
>> +         * zoned devices.
>> +         */
>> +        if (!is_power_of_2(zone->len) && zone->capacity < zone->len) {
>> +            pr_err("%s: Invalid zone capacity %lld with non 
>> power-of-2 zone size %lld",
>> +                   disk->disk_name, zone->capacity, zone->len);
>>               return -ENODEV;
>>           }
>>           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);
>>       } 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 84e7881262e3..d0d66a0db224 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -704,6 +704,30 @@ 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;
> See below
> 
>> +
>> +    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_start(struct block_device *bdev, 
>> sector_t sec)
>> +{
>> +    if (!bdev_is_zoned(bdev))
>> +        return false;
> Duplicating the same check above, and the check above is less clear in 
> the case of !zoned since it returns 0 and not some warning that makes 
> sense in the case of zoned check on !zoned bdev.
> Can you simply exclude above check?
Nevermind, just noticed bdev_offset_from_zone_start is used in later 
patches.

> 
> 
>> +
>> +    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))
>> @@ -748,6 +772,12 @@ static inline unsigned int disk_zone_no(struct 
>> gendisk *disk, sector_t sector)
>>   {
>>       return 0;
>>   }
>> +
>> +static inline bool bdev_is_zone_start(struct block_device *bdev, 
>> sector_t sec)
>> +{
>> +    return false;
>> +}
>> +
>>   static inline unsigned int bdev_max_open_zones(struct block_device 
>> *bdev)
>>   {
>>       return 0;

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