linux-kernel - Re: [PATCH v2 5/5] block: use chunk_sectors when evaluating stacked atomic write limits

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Message-ID: <ef5aceb9-a5ec-489c-88e3-f674d59299ad@linux.ibm.com>
Date: Fri, 20 Jun 2025 20:03:50 +0530
From: Nilay Shroff <nilay@...ux.ibm.com>
To: John Garry <john.g.garry@...cle.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 v2 5/5] block: use chunk_sectors when evaluating stacked
 atomic write limits



On 6/18/25 2:07 PM, John Garry wrote:
> The atomic write unit max value is limited by any stacked device stripe
> size.
> 
> It is required that the atomic write unit is a power-of-2 factor of the
> stripe size.
> 
> Currently we use io_min limit to hold the stripe size, and check for a
> io_min <= SECTOR_SIZE when deciding if we have a striped stacked device.
> 
> Nilay reports that this causes a problem when the physical block size is
> greater than SECTOR_SIZE [0].
> 
> Furthermore, io_min may be mutated when stacking devices, and this makes
> it a poor candidate to hold the stripe size. Such an example (of when
> io_min may change) would be when the io_min is less than the physical
> block size.
> 
> Use chunk_sectors to hold the stripe size, which is more appropriate.
> 
> [0] https://lore.kernel.org/linux-block/888f3b1d-7817-4007-b3b3-1a2ea04df771@linux.ibm.com/T/#mecca17129f72811137d3c2f1e477634e77f06781
> 
> Signed-off-by: John Garry <john.g.garry@...cle.com>

Looks good to me:
Reviewed-by: Nilay Shroff <nilay@...ux.ibm.com>