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Date:   Mon, 11 Apr 2022 22:27:54 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Mike Snitzer <snitzer@kernel.org>
Cc:     linux-block@vger.kernel.org, Christoph Hellwig <hch@infradead.org>,
        Dennis Zhou <dennis@kernel.org>, tj@kernel.org,
        axboe@kernel.dk, dm-devel@redhat.com
Subject: Re: [PATCH] block: remove redundant blk-cgroup init from __bio_clone
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On Mon, Apr 11, 2022 at 01:33:58PM -0400, Mike Snitzer wrote:
> When bio_{alloc,init}_clone are passed a bdev, bio_init() will call
> bio_associate_blkg() so the __bio_clone() work to initialize blkcg
> isn't needed.

No, unfortunately it isn't as simple as that.  There are bios that do
not use the default cgroup and thus blkg, e.g. those that come from
cgroup writeback.