linux-kernel - Re: [dm-devel] [PATCH v7 02/13] block: allow blk-zoned devices to have non-power-of-2 zone size

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Message-ID: <e04db101-5628-2a1d-6b5c-997090484d7d@samsung.com>
Date:   Thu, 16 Jun 2022 12:09:35 +0200
From:   Pankaj Raghav <p.raghav@...sung.com>
To:     Bart Van Assche <bvanassche@....org>, <hch@....de>,
        <snitzer@...hat.com>, <damien.lemoal@...nsource.wdc.com>,
        <axboe@...nel.dk>
CC:     <pankydev8@...il.com>, <gost.dev@...sung.com>,
        <jiangbo.365@...edance.com>, <linux-nvme@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-block@...r.kernel.org>,
        <dm-devel@...hat.com>, <jonathan.derrick@...ux.dev>,
        <Johannes.Thumshirn@....com>, <dsterba@...e.com>,
        <jaegeuk@...nel.org>, "Luis Chamberlain" <mcgrof@...nel.org>
Subject: Re: [dm-devel] [PATCH v7 02/13] block: allow blk-zoned devices to
 have non-power-of-2 zone size

On 2022-06-15 22:28, Bart Van Assche wrote:
isk_name, zone->len);
>> +        if (zone->len == 0) {
>> +            pr_warn("%s: Invalid zone size", disk->disk_name);
>> +            return -ENODEV;
>> +        }
>> +
>> +        /*
>> +         * Don't allow zoned device with non power_of_2 zone size with
>> +         * zone capacity less than zone size.
>> +         */
> 

> Please change "power_of_2" into "power-of-2".
> 
Ok.
>> +        if (!is_power_of_2(zone->len) && zone->capacity < zone->len) {
>> +            pr_warn("%s: Invalid zone capacity for non power of 2
>> zone size",
>> +                disk->disk_name);
>>               return -ENODEV;
>>           }
> 
> The above check seems wrong to me. I don't see why devices that report a
> capacity that is less than the zone size should be rejected.
> 
This was brought up by Damien during previous reviews. The argument was
that the reason to allow non power-of-2 zoned device is to remove the
gaps between zone size and zone capacity. Allowing a npo2 zone size with
a different capacity, even though it is technically possible, it does
not make any practical sense. That is why this check was introduced.
Does that answer your question?
>> +        /*
>> +         * 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.
>> +         */
> 
> Shouldn't the above comment be moved to the patch description? I'm not
> sure whether having such a comment in the source code is valuable.
> 
Yeah, I will remove it. Maybe it is very obvious at this point.
>> +static inline sector_t blk_queue_offset_from_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;
> 
> "return false" should only occur in functions returning a boolean. This
> function returns type sector_t.
> 
Good catch. It was a copy paste mistake. Fixed it.
> Thanks,
> 
> Bart.