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Date:   Thu, 31 Mar 2022 02:15:24 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Dennis Zhou <dennis@kernel.org>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Mike Snitzer <snitzer@kernel.org>, tj@kernel.org,
        axboe@kernel.dk, linux-block@vger.kernel.org, dm-devel@redhat.com
Subject: Re: can we reduce bio_set_dev overhead due to bio_associate_blkg?
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On Wed, Mar 30, 2022 at 10:52:13PM -0700, Dennis Zhou wrote:
> I took a quick look. It seems with the new interface,
> bio_clone_blkg_association() is unnecessary given the correct
> association should be derived from the bio_alloc*() calls with the
> passed in bdev. Also, blkcg_bio_issue_init() in clone seems wrong.

Yes, I think you are right.

> Maybe the right thing to do here for md-linear and btrfs (what I've
> looked at) is to delay cloning until the map occurs and the right device
> is already in hand?

That would in general be the preferred option where possible.