linux-kernel - Re: [PATCH 04/16] block: allow blk-zoned devices to have non-power-of-2 zone size

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Date:   Thu, 28 Apr 2022 21:04:16 +0200
From:   Pankaj Raghav <p.raghav@...sung.com>
To:     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 04/16] block: allow blk-zoned devices to have
 non-power-of-2 zone size

On 2022-04-28 01:37, Damien Le Moal wrote:
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 937bb6b86331..850caf311064 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -634,8 +634,7 @@ 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 (pos & (blk_queue_zone_sectors(q) - 1) ||
>> -	    !blk_queue_zone_is_seq(q, pos))
>> +	if (!blk_queue_zone_aligned(q, pos) || !blk_queue_zone_is_seq(q, pos))
> 
> blk_queue_zone_aligned() is a little confusing since "aligned" is also
> used for write-pointer aligned. I would rename this helper
> 
> blk_queue_is_zone_start()
> 
> or something like that.
> 
That is a good idea and definitely a better name that
blk_queue_zone_aligned. I will fix it.

>>  	/*
>> @@ -489,14 +489,14 @@ 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 zoned device size",
>> +				disk->disk_name);
> 
> The message is weird now. Please change it to "Invalid zone size".
> 
Ok.
> Also, the entire premise of this patch series is that it is hard for
> people to support the unusable sectors between zone capacity and zone end
> for drives with a zone capacity smaller than the zone size.
> 
> Yet, here you do not check that zone capacity == zone size for drives that
> do not have a zone size equal to a power of 2 number of sectors. This
> means that we can still have drives with ZC < ZS AND ZS not equal to a
> power of 2. So from the point of view of your arguments, no gains at all.
> Any thoughts on this ?
> 
That is a good point. Instead of implicitly assuming npo2 drives to have
ZC == ZS, it is better to be explicit during bringup. Thanks. As Luis
mentioned, I will add this condition in the next revision.