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Subject: Re: [PATCH 1/6] block: cache bdev in struct file for raw bdev IO
To:     Pavel Begunkov <asml.silence@gmail.com>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
References: <cover.1633781740.git.asml.silence@gmail.com>
 <cfc66d9946422fa1778504f976621c91be2befb5.1633781740.git.asml.silence@gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <0785c707-ba82-1e46-5d4d-63ccacdb471f@kernel.dk>
Date:   Sat, 9 Oct 2021 10:33:17 -0600
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On 10/9/21 6:25 AM, Pavel Begunkov wrote:
> bdev = &BDEV_I(file->f_mapping->host)->bdev
> 
> Getting struct block_device from a file requires 2 memory dereferences
> as illustrated above, that takes a toll on performance, so cache it in
> yet unused file->private_data. That gives a noticeable peak performance
> improvement.

It's hilariously bad right now, so I really welcome this change. One
comment:

> +static inline struct block_device *blkdev_get_bdev(struct file *file)
> +{
> +	return file->private_data;
> +}

Get rid of this and just use bdev = file->private_data where
appropriate. Easier to read, we don't need to hide this in a function.

-- 
Jens Axboe