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Message-ID: <b6af511e-9128-4775-8994-9bbaef3465a2@cybernetics.com>
Date: Tue, 29 Jul 2025 17:49:07 -0400
From: Tony Battersby <tonyb@...ernetics.com>
To: yukuai@...nel.org, Song Liu <song@...nel.org>,
 Yu Kuai <yukuai3@...wei.com>, Christian Brauner <brauner@...nel.org>,
 "Darrick J. Wong" <djwong@...nel.org>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: linux-raid@...r.kernel.org, linux-xfs@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] md/raid0,raid4,raid5,raid6,raid10: fix bogus io_opt
 value

On 7/29/25 12:56, Yu Kuai wrote:
> Hi,
>
> 在 2025/7/30 0:12, Tony Battersby 写道:
>> md-raid currently sets io_min and io_opt to the RAID chunk and stripe
>> sizes and then calls queue_limits_stack_bdev() to combine the io_min and
>> io_opt values with those of the component devices.  The io_opt size is
>> notably combined using the least common multiple (lcm), which does not
>> work well in practice for some drives (1), resulting in overflow or
>> unreasonable values.
>>
>> dm-raid, on the other hand, sets io_min and io_opt through the
>> raid_io_hints() function, which is called after stacking all the queue
>> limits of the component drives, so the RAID chunk and stripe sizes
>> override the values of the stacking.
>>
>> Change md-raid to be more like dm-raid by setting io_min and io_opt to
>> the RAID chunk and stripe sizes after stacking the queue limits of the
>> component devies.  This fixes /sys/block/md0/queue/optimal_io_size from
>> being a bogus value like 3221127168 to being the correct RAID stripe
>> size.
> This is already discussed, and mtp3sas should fix this strange value.

Thanks, I will follow that ongoing discussion.

https://lore.kernel.org/all/ywsfp3lqnijgig6yrlv2ztxram6ohf5z4yfeebswjkvp2dzisd@f5ikoyo3sfq5/