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Date: Wed, 16 Jul 2025 13:41:22 +0200
From: Christoph Hellwig <hch@lst.de>
To: Coly Li <i@coly.li>
Cc: Christoph Hellwig <hch@lst.de>, colyli@kernel.org,
	linux-raid@vger.kernel.org, linux-block@vger.kernel.org,
	Yu Kuai <yukuai3@huawei.com>, Xiao Ni <xni@redhat.com>,
	Hannes Reinecke <hare@suse.de>, Martin Wilck <mwilck@suse.com>,
	Keith Busch <kbusch@kernel.org>
Subject: Re: [RFC PATCH] md: split bio by io_opt size in md_submit_bio()
Message-ID: <20250716114121.GA32207@lst.de>
References: <20250715180241.29731-1-colyli@kernel.org> <20250716113737.GA31369@lst.de> <437E98DD-7D64-49BF-9F2C-04CB0A142A88@coly.li>
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On Wed, Jul 16, 2025 at 07:39:18PM +0800, Coly Li wrote:
> >> For raid level 4/5/6 such split method might be problematic and hurt
> >> large read/write perforamnce. Because limits.max_hw_sectors are not
> >> always aligned to limits.io_opt size, the split bio won't be full
> >> stripes covered on all data disks, and will introduce extra read-in I/O.
> >> Even the bio's bi_sector is aligned to limits.io_opt size and large
> >> enough, the resulted split bio is not size-friendly to corresponding
> >> raid456 level.
> > 
> > So why don't you set a sane max_hw_sectors value instead of duplicating
> > the splitting logic?
> 
> Can you explain a bit more detail?  In case I misunderstand you like I
> did with Kuai’s comments

Just set the max_hw_sectors you want.