Re: [PATCH v4 02/13] block: allow blk-zoned devices to have non-power-of-2 zone size

Pankaj Raghav
2022-05-16T19:05:47Z

Hi Damien,
I copied your comments from the previous thread to avoid confusion.

On 2022-05-16 16:00, Damien Le Moal wrote:
> On 2022/05/16 15:39, Pankaj Raghav wrote:
>> Checking if a given sector is aligned to a zone is a common
>> operation that is performed for zoned devices. Add
>> blk_queue_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 based logic in the block layer using the helpers wherever
>> possible.
>>
>> @@ -490,14 +490,29 @@ 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 zone size",
>> + disk->disk_name);
>
> This fits on one line, no ?
>
Yeah. I don't know why my formatter decided to do that. I will fix it. Thanks.
>> + return -ENODEV;
>> + }
>> +
>> + /*
>> + * Don't allow zoned device with non power_of_2 zone size with
>> + * zone capacity less than zone size.
>> + */
>> + if (!is_power_of_2(zone->len) &&
>> + zone->capacity < zone->len) {
>> + pr_warn("%s: Invalid zoned size with non power of 2 zone size and zone capacity < zone size",
>> + disk->disk_name);
>
> Very long... What about:
>
> pr_warn("%s: Invalid zone capacity for non power of 2 zone size",
> disk->disk_name);
>
This looks better. I will fix it up!
>> return -ENODEV;
>> }
>>
>> args->zone_sectors = zone->len;
>> - args->nr_zones = (capacity + zone->len - 1) >> ilog2(zone->len);
>> + /*
>> + * Division is used to calculate nr_zones for both power_of_2
>> + * and non power_of_2 zone sizes as it is not in the hot path.
>> + */
>
> This comment is not very useful.
>

I also saw you mentioning the comment was not useful in nvme code for
a similar scenario. Hannes brought up a point about making it
explicit when we are not using any special path for power of 2 zone sizes as in
most cases we do branching if the zone size is power of 2 to avoid division.

>> + 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 22fe512ee..32d7bd7b1 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -686,6 +686,22 @@ static inline unsigned int blk_queue_zone_no(struct request_queue *q,
>> return div64_u64(sector, zone_sectors);
>> }
>>
>> +static inline bool blk_queue_is_zone_start(struct request_queue *q, sector_t sec)
>> +{
>> + sector_t zone_sectors = blk_queue_zone_sectors(q);
>> + u64 remainder = 0;
>> +
>> + if (!blk_queue_is_zoned(q))
>> + return false;
>> +
>> + if (is_power_of_2(zone_sectors))
>> + return IS_ALIGNED(sec, zone_sectors);
>> +
>> + div64_u64_rem(sec, zone_sectors, &remainder);
>> + /* if there is a remainder, then the sector is not aligned */
>
> Hmmm... Fairly obvious. Not sure this comment is useful.
>
True. I will remove it.

>> + return remainder == 0;
>> +}
>> +
>> static inline bool blk_queue_zone_is_seq(struct request_queue *q,
>> sector_t sector)
>> {
>> @@ -732,6 +748,12 @@ static inline unsigned int blk_queue_zone_no(struct request_queue *q,
>> {
>> return 0;
>> }
>> +
>> +static inline bool blk_queue_is_zone_start(struct request_queue *q, sector_t sec)
>> +{
>> + return false;
>> +}
>> +
>> static inline unsigned int queue_max_open_zones(const struct request_queue *q)
>> {
>> return 0;
>
>