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Date: Tue, 13 May 2025 08:44:34 +0200
From: Christoph Hellwig <hch@lst.de>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>, Damien Le Moal <dlemoal@kernel.org>,
	Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH] block: Split bios in LBA order
Message-ID: <20250513064434.GA1199@lst.de>
References: <20250512225623.243507-1-bvanassche@acm.org>
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In-Reply-To: <20250512225623.243507-1-bvanassche@acm.org>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, May 12, 2025 at 03:56:23PM -0700, Bart Van Assche wrote:
> The block layer submits bio fragments in opposite LBA order. Fix this as
> follows:
> - Introduce a new function bio_split_to_limits_and_submit() that has the
>   same behavior as the existing bio_split_to_limits() function. This
>   involves splitting a bio and submitting the fragment with the highest
>   LBA by calling submit_bio_noacct().
> - Use the new function bio_split_to_limits_and_submit() in all drivers
>   that are fine with submitting split bios in opposite LBA order.

If you have to rename a user visible symbol, please do that in a
preparation patch.

Also how do you determine some drivers are fine with one order while
others are not?

> - Modify blk_mq_submit_bio() and dm_split_and_process_bio() such that
>   bio fragments are submitted in LBA order.

blk_mq_submit_bio calls __bio_split_to_limits, which returns the
bio split off the beginning of the passed in bio by bio_submit_split.
I don't see how that would reorder anything.