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Date:   Fri, 30 Nov 2018 01:54:26 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Dennis Zhou <dennis@kernel.org>
Cc:     Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Josef Bacik <josef@toxicpanda.com>, kernel-team@fb.com,
        linux-block@vger.kernel.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 05/13] blkcg: associate blkg when associating a device
Message-ID: <20181130095426.GB17103@infradead.org>
References: <20181126211946.77067-1-dennis@kernel.org>
 <20181126211946.77067-6-dennis@kernel.org>
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> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 62715a5a4f32..8bc9d9b29fd3 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -486,6 +486,12 @@ extern unsigned int bvec_nr_vecs(unsigned short idx);
>  extern const char *bio_devname(struct bio *bio, char *buffer);
>  
>  #define bio_set_dev(bio, bdev) 			\
> +do {						\
> +	bio_set_dev_only(bio, bdev);		\
> +	bio_associate_blkg(bio);		\
> +} while (0)
> +
> +#define bio_set_dev_only(bio, bdev)		\

This lacks any explanation on when you would use bio_set_dev_only or
bio_set_dev.  Please document why we need both and why you'd choose or
the other.