linux-kernel - Re: [PATCH RFC 4/4] block: use chunk_sectors when evaluating stacked atomic write limits

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Message-ID: <c7e4e1ad-a0d8-4eb5-8f88-6607939b1918@oracle.com>
Date: Thu, 12 Jun 2025 10:17:48 +0100
From: John Garry <john.g.garry@...cle.com>
To: Nilay Shroff <nilay@...ux.ibm.com>, agk@...hat.com, snitzer@...nel.org,
        mpatocka@...hat.com, song@...nel.org, yukuai3@...wei.com, hch@....de,
        axboe@...nel.dk
Cc: dm-devel@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-raid@...r.kernel.org, linux-block@...r.kernel.org,
        ojaswin@...ux.ibm.com, martin.petersen@...cle.com
Subject: Re: [PATCH RFC 4/4] block: use chunk_sectors when evaluating stacked
 atomic write limits

On 06/06/2025 16:23, Nilay Shroff wrote:
>>   	t->atomic_write_hw_unit_min = min(b->atomic_write_hw_unit_min,
>>   					  t->atomic_write_hw_unit_max);
>> -	t->atomic_write_hw_max = min(b->atomic_write_hw_max, t->io_min);
>> +	t->atomic_write_hw_max = min(b->atomic_write_hw_max, chunk_size);
>>   
>>   	return true;
>>   }
> This works well with my NVMe disk which supports atomic writes however the only
> concern is what if in case t->chunk_sectors is also defined for NVMe disk?
> I see that nvme_set_chunk_sectors() initializes the chunk_sectors for NVMe.
> The value which is assigned to lim->chunk_sectors in nvme_set_chunk_sectors()
> represents "noiob" (i.e. Namespace Optimal I/O Boundary). My disk has "noiob"
> set to zero but in case if it's non-zero then would it break the above logic
> for NVMe atomic writes?

Yeah, I think that I need to change the code to account for the bottom 
device setting chunk_sectors.

Thanks,
John