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Date:   Tue, 21 Mar 2023 07:05:30 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        Christoph Hellwig <hch@lst.de>, Ming Lei <ming.lei@redhat.com>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        Johannes Thumshirn <johannes.thumshirn@wdc.com>
Subject: Re: [PATCH v2 2/3] block: Split and submit bios in LBA order
Message-ID: <20230321060530.GC18078@lst.de>
References: <20230320234905.3832131-1-bvanassche@acm.org> <20230320234905.3832131-3-bvanassche@acm.org> <20230321060307.GB18078@lst.de>
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On Tue, Mar 21, 2023 at 07:03:07AM +0100, Christoph Hellwig wrote:
> > +		if (current->bio_list) {
> > +			/*
> > +			 * The caller will submit the first half ('split')
> > +			 * before the second half ('bio').
> > +			 */
> > +			bio_chain(split, bio);
> > +			submit_bio_noacct(bio);
> > +			return split;
> > +		}
> > +		/*
> > +		 * Submit the first half ('split') let the caller submit the
> > +		 * second half ('bio').
> > +		 */
> > +		*nr_segs = bio_chain_nr_segments(bio, lim);
> > +		bio_chain(split, bio);
> > +		submit_bio_noacct(split);
> 
> I'm really confused on why you want to change the behavior here
> for the case where run in a stacking context vs not, and neither
> the comments nor the commit log help me trying to figure out why.

In fact I wonder how you managed to get into __bio_split_to_limits
wtih a NULL current->bio_list at all.