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Date: Mon, 8 Apr 2024 10:47:39 +0200
From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, janpieter.sollie@edpnet.be,
	Mike Snitzer <snitzer@kernel.org>, dm-devel@lists.linux.dev,
	Song Liu <song@kernel.org>, linux-raid@vger.kernel.org
Subject: Re: [PATCH] block: allow device to have both virt_boundary_mask
 and max segment size
Message-ID: <20240408084739.GA26968@lst.de>
References: <20240407131931.4055231-1-ming.lei@redhat.com> <20240408055542.GA15653@lst.de> <ZhOekuZdwlwNSiZV@fedora>
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On Mon, Apr 08, 2024 at 03:36:50PM +0800, Ming Lei wrote:
> It isn't now we put the limit, and this way has been done for stacking device
> since beginning, it is actually added by commit d690cb8ae14b in v6.9-rc1.
> 
> If max segment size isn't aligned with virt_boundary_mask, bio_split_rw()
> will split the bio with max segment size, this way still works, just not
> efficiently. And in reality, the two are often aligned.

We've had real bugs due to this, which is why we have the check.  We also
had a warning before the commit, it's just it got skipped for
stacking.  So even if we want to return to the broken pre-6.9-rc behavior
it should only be for stacking.  I don't think that is a good outcome,
though.