linux-kernel - Re: [PATCH 05/16] nvme: zns: Allow ZNS drives that have non-power_of

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Date:   Wed, 4 May 2022 20:55:43 +0200
From:   Pankaj Raghav <p.raghav@...sung.com>
To:     Hannes Reinecke <hare@...e.de>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        <jaegeuk@...nel.org>, <axboe@...nel.dk>, <snitzer@...nel.org>,
        <hch@....de>, <mcgrof@...nel.org>, <naohiro.aota@....com>,
        <sagi@...mberg.me>, <dsterba@...e.com>,
        <johannes.thumshirn@....com>
CC:     <linux-kernel@...r.kernel.org>, <clm@...com>,
        <gost.dev@...sung.com>, <chao@...nel.org>, <josef@...icpanda.com>,
        <jonathan.derrick@...ux.dev>, <agk@...hat.com>,
        <kbusch@...nel.org>, <kch@...dia.com>,
        <linux-nvme@...ts.infradead.org>, <bvanassche@....org>,
        <jiangbo.365@...edance.com>, <matias.bjorling@....com>,
        <linux-block@...r.kernel.org>
Subject: Re: [PATCH 05/16] nvme: zns: Allow ZNS drives that have
 non-power_of_2 zone size

On 2022-05-04 19:03, Hannes Reinecke wrote:
> On 4/27/22 09:02, Pankaj Raghav wrote:
>> Remove the condition which disallows non-power_of_2 zone size ZNS drive
>> to be updated and use generic method to calculate number of zones
>> instead of relying on log and shift based calculation on zone size.
>>
>> The power_of_2 calculation has been replaced directly with generic
>> calculation without special handling. Both modified functions are not
>> used in hot paths, they are only used during initialization &
>> revalidation of the ZNS device.
>>
>> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
>> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
>> ---
     }
>>         ns->zsze = nvme_lba_to_sect(ns,
>> le64_to_cpu(id->lbafe[lbaf].zsze));
>> -    if (!is_power_of_2(ns->zsze)) {
>> -        dev_warn(ns->ctrl->device,
>> -            "invalid zone size:%llu for namespace:%u\n",
>> -            ns->zsze, ns->head->ns_id);
>> -        status = -ENODEV;
>> -        goto free_data;
>> -    }
>>         blk_queue_set_zoned(ns->disk, BLK_ZONED_HM);
>>       blk_queue_flag_set(QUEUE_FLAG_ZONE_RESETALL, q);
>> @@ -129,7 +122,7 @@ static void *nvme_zns_alloc_report_buffer(struct
>> nvme_ns *ns,
>>                      sizeof(struct nvme_zone_descriptor);
>>         nr_zones = min_t(unsigned int, nr_zones,
>> -             get_capacity(ns->disk) >> ilog2(ns->zsze));
>> +             div64_u64(get_capacity(ns->disk), ns->zsze));
>>   
> Same here; please add a helper calculating the number of zones for a
> given disk.
> 
I am already  using the div64_u64 helper and this is not done again
anywhere in the nvme zns driver. I am not sure if having a separate
helper for this will add value. And this is not in the hot path, so no
need for special handling.
>>       bufsize = sizeof(struct nvme_zone_report) +
>>           nr_zones * sizeof(struct nvme_zone_descriptor);
>> @@ -197,7 +190,7 @@ int nvme_ns_report_zones(struct nvme_ns *ns,
>> sector_t sector,
>>       c.zmr.zrasf = NVME_ZRASF_ZONE_REPORT_ALL;
>>       c.zmr.pr = NVME_REPORT_ZONE_PARTIAL;
>>   -    sector &= ~(ns->zsze - 1);
>> +    sector = rounddown(sector, ns->zsze);
>>       while (zone_idx < nr_zones && sector < get_capacity(ns->disk)) {
>>           memset(report, 0, buflen);
>>   
> Please be a bit more consistent. In the previous patches you always had
> a condition to check if it's a power_of_2 zone size, but here you are
> using the same calculation for each disk.
> So please use the check in all locations, or add a comment why the
> generic calculation is okay to use here.
> 
That is a good point. I have mentioned that in my commit log that I am
not having any special handling because these calculations are not in
the hot path.

Maybe adding comments is better for clarity. I will also do it for your
previous comment.

I will queue this up for my next revision. Thanks.
> Cheers,
> 
> Hannes